Radiation Effects in Materials 978-953-51-2418-4

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Radiation Effects in Materials Edited by Waldemar A. Monteiro

Radiation Effects in Materials Edited by Waldemar A. Monteiro

Published by ExLi4EvA Copyright © 2016 All chapters are Open Access distributed under the Creative Commons Attribution 3.0 license, which allows users to download, copy and build upon published articles even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. After this work has been published, authors have the right to republish it, in whole or part, in any publication of which they are the author, and to make other personal use of the work. Any republication, referencing or personal use of the work must explicitly identify the original source. As for readers, this license allows users to download, copy and build upon published chapters even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. Notice Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book.

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Contents

Preface

Chapter 1 Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers by Alexander V. Kir’yanov Chapter 2 Radiation Effects in Optical Materials and Photonic Devices by Dan Sporea and Adelina Sporea Chapter 3 The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors by Dejan Nikolić and Aleksandra Vasić-Milovanović Chapter 4 Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends by R. Deepalaxmi, V. Rajini and C. Vaithilingam Chapter 5 Radiation and Environmental Biophysics: From Single Cells to Small Animals by Yanping Xu Chapter 6 Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident by Markus Zehringer Chapter 7 Radiation Influence on Edible Materials by Nelida Lucia del Mastro Chapter 8 Transient Anions in Radiobiology and Radiotherapy: From Gaseous Biomolecules to Condensed Organic and Biomolecular Solids by Elahe Alizadeh, Sylwia Ptasińska and Léon Sanche

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Chapter 9 Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation by Jean Engohang-Ndong and Roberto M. Uribe Chapter 10 Radiation Effects in Polyamides by Mária Porubská Chapter 11 Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials by Taras S. Kavetskyy and Andrey L. Stepanov Chapter 12 Radiation Effects in Textile Materials by Sheila Shahidi and Jakub Wiener Chapter 13 Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production by Mohd Asyraf Kassim, H.P.S Abdul Khalil, Noor Aziah Serri, Mohamad Haafiz Mohamad Kassim, Muhammad Izzuddin Syakir, N.A. Sri Aprila and Rudi Dungani Chapter 14 Ion Bombardment-Induced Surface Effects in Materials by Farid F. Umarov and Abdiravuf A. Dzhurakhalov Chapter 15 Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review by Murthy Kolluri Chapter 16 A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids by Mihai Oane, Rareş Victor Medianu and Anca Bucă Chapter 17 Nanostructuring of Material Surfaces by Laser Ablation by Cinthya Toro Salazar, María Laura Azcárate and Carlos Alberto Rinaldi

Preface

The study of radiation effects has developed as a major field of materials science from the beginning, approximately 70 years ago. Its rapid development has been driven by two strong influences. The properties of the crystal defects and the materials containing them may then be studied. The types of radiation that can alter structural materials consist of neutrons, ions, electrons, gamma rays or other electromagnetic waves with different wavelengths. All of these forms of radiation have the capability to displace atoms/molecules from their lattice sites, which is the fundamental process that drives the changes in all materials. The effect of irradiation on materials is fixed in the initial event in which an energetic projectile strikes a target. The book is distributed in four sections: Ionic Materials; Biomaterials; Polymeric Materials and Metallic Materials.

Chapter 1

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers Alexander V. Kir’yanov Additional information is available at the end of the chapter http://dx.doi.org/10.5772/63939

Abstract “ review oλ the recent studies oλ the eλλect oλ irradiatinμ silica-based λibers doped with rare earths and metals by a beam oλ hiμh-enerμy β electrons is presented. Oλ the review’s main scope are the attenuation spectra’ transλormations occurrinμ in optical λiber oλ such types under electron irradiation, allowinμ, λrom one side, to recover some μeneral essence oλ the phenomena involved and, λrom the other side, to draw the λeatures that would make such λibers useλul λor applications, λor example, in dosime‐ try and space technoloμies. “monμ the λibers oλ the current review’s choice, exempli‐ λyinμ the eλλect oλ electron irradiation most briμhtly, are ytterbium Yb and cerium Ce the rare earths’ representatives and bismuth ”i the post-transitional metals representative doped λibers, where a diversity oλ the electron-irradiation-related eλλects is encouraμed. Keywords: electron irradiation, ytterbium-, cerium- and bismuth-doped silica λibers, photodarkeninμ, optical bleachinμ

. Introduction In this chapter, a λew examples are demonstrated oλ the impact oλ hiμh-enerμy β electrons irradiation on the absorptive and λluorescence properties oλ silica-based optical λibers doped with rare earths and metals. The results presented hereaλter seem to be useλul λor understand‐ inμ the processes standinμ behind the hiμhliμhted phenomena and λor possible applications oλ the λibers, say, in dosimetry and space technoloμy. In each case, we used λor irradiatinμ λiber samples a controllable linear accelerator oλ the LU type that emits β-electrons with a narrow-band enerμy spectrum ~ MeV in a shortpulse ~ μs mode. The samples with lenμths oλ around – m were placed into the

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accelerator’s chamber λor various time intervals, which provided μrowinμ irradiation doses. The irradiated λibers were then leλt λor weeks prior to the main-course spectral measure‐ ments to avoid the role oλ short-livinμ components in the decay oλ induced absorption I“ . The measurements were done durinμ a limited time viz., the λollowinμ … weeks λor diminishinμ the eλλect oλ spontaneous I“ recoverinμ. Note that ionization, that is, the production oλ β-induced carriers by an electron beam i.e., oλ secondary λree holes and electrons , is the main cause oλ the spectral transλormations in the λibers. This happens because hiμh-enerμy primary β-electrons are virtually nondissipatinμ at the propaμation throuμh a λiber sample on the other hand, certain contribution in ionization oλ the λibers’ core-μlasses arisinμ λrom γ-quanta born at inelastic scatterinμ oλ the hiμh-enerμy electrons cannot be disreμarded. We demonstrate below λirst a study oλ the resistance oλ a couple oλ cerium Ce -doped alumino-phospho-silicate λibers one oλ them beinμ codoped with μold “u , to β-electrons. The experimental data reveal a severe eλλect oλ β-irradiation upon the λibers’ absorptive properties, μiven by noticeable susceptibility oλ Ce ions beinμ in Ce +/Ce + states to the treatment, arisinμ as μrowth λollowed by saturation oλ I“. We also report the essentials oλ posterior bleachinμ oλ β-darkened λibers, also in terms oλ attenuation spectra’ transλorma‐ tions, at exposinμ them to low-power μreen a He-Ne laser and ultra violet UV, a mercury lamp liμht. It is shown that both phenomena are less expressed in Ce λiber codoped with “u than in “u-λree one and that the spectral chanμes in the λormer are more reμular versus dose and bleachinμ time. Then, we provide a comparative experimental analysis oλ I“, induced by β-electrons, λor a series oλ ytterbium Yb -doped alumino-μermano-silicate λibers with diλλerent concentrations oλ Yb + ions and compare this eλλect with the photodarkeninμ PD phenomenon in the same λibers, arisinμ at resonant into nm absorption peak oλ Yb + ions optical pumpinμ. The experimental data obtained reveals that, in these two circumstances, substantial and complex but diλλerent in appearance chanμes aλλectinμ the resonant absorption band oλ Yb + ions and the oλλ-resonance backμround loss are produced in the λibers. Finally, we report a study oλ attenuation spectra’ transλormations in a set oλ bismuth ”i -doped silica λibers with various contents oλ emission-active ”i centers, which occur as the result oλ β-irradiation. “monμ the data obtained, notice a substantial decrease oλ concentration oλ ”i centers, associated with the presence oλ Germanium Ge in core-μlass, with increasinμ irradiation dose the bleachinμ€ eλλect , while, on the contrary, an opposite trend, that is, dosedependent μrowth oλ resonant-absorption ascribed to ”i active centers, associated with the presence in core-μlass oλ “luminium “l . These results are worth noticinμ λor understandinμ the nature oλ ”i-related centers in silica λibers, yet uncovered.

. The effects of electron irradiation and posterior optical bleaching in Ce-doped and Ce/Au-codoped alumino-phospho-silicate fibers Development oλ suitable host μlasses and λibers λor dosimetry, which are based on λormation oλ radiation-induced deλects leadinμ to μlass coloration [ – ] or λillinμ pre-existinμ traps,

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

measured by means oλ thermally or optically stimulated λluorescence [ ], became a hot task. Dosimetry systems can be used in hiμh radiation λields, λor example, in proximity to nuclear reactors, hazardous places, and in open space. Fiber-based dosimeters are beinμ intensively investiμated and recently a λew systems have been proposed, based on versatile physical eλλects in radiation-sensitive silica λibers [ ]. Cerium Ce -doped silica μlass has interestinμ λluorescent properties [ ], which makes it promisinμ λor utilizinμ as a scintillator λor detectinμ X- and γ-rays, or neutrons [ , ]. On the other hand, silica μlass is known to suλλer λrom the presence oλ point deλects and OH μroups, responsible λor nonradiative recombination channels competinμ λluorescence. In turn, “u, when combined with cerium oxide CeO is known to be a promisinμ catalyst λor the reaction CO + H O→H + CO [ , ], μivinμ a way to remove carbon-related impurities alonμ with OH μroups λrom silica matrix durinμ synthesis. Thus, Ce/“u codoped μlass is expected to enhance eλλiciency oλ enerμy transλer λrom the host matrix to emissive centers. The other motivation λor “u codopinμ is to increase radiation resistance oλ Ce-doped λiber, as arμued in more details below. The reλereed properties oλ alumino-phospho-silicate μlass doped with Ce and Ce/“u are also a concern oλ optical λibers made on its base. ”elow, the results oλ experiments on irradiatinμ Ce-doped alumino-phospho-silicate λibers by enerμetic β-electrons are hiμhliμhted, resultinμ in the λibers darkeninμ. It is λurthermore shown that the irradiated λibers are sensitive to weak liμht oλ a He-Ne laser nm and UV mercury lamp, both leadinμ to partial recovery oλ their initial properties. The whole oλ experimental data evidences notable susceptibility oλ Ce-doped λibers to both kinds oλ treatment. “s well, it is demonstrated that the spectral transλormations occurrinμ in Ce λiber codoped with “u are less expressed but more reμular upon β-irradiation dose and exposure time when bleachinμ than those in “u-λree λiber. “ brieλ discussion in attempt oλ a reasonable explanation oλ the experimental laws completes the study, with the key point beinμ a discussion about the species involved in the processes, which are associated with Ce. The reported results may have value λor usinμ Ce-doped silica λibers λor dosimetry in harmλul environments [ , – ] and inscribinμ ”raμμ μratinμs [ – ]. “s well, these results seem to be impactλul, μiven by renewed interest to Ce codopinμ as a tool λor diminishinμ PD in Ybdoped λibers we inspect the last eλλect in detail in Paraμraph . . . Fiber samples and experimental arrangement The sourcinμ Ce-doped and Ce/“u-codoped λiber preλorms based on alumino-phosphosilicate μlass have been made by means oλ modiλied chemical vapor deposition MCVD process employed in conjunction with solution dopinμ SD technique the λinal λibers have been drawn λrom the preλorms usinμ a drawinμ tower. Core diameters/numerical apertures oλ the two λibers were measured to be ~ μm/ . … . , respectively. Estimated λrom EDX, averaμe dopinμ levels were λound to be . wt.% “l O , . wt.% P O , . wt.% CeO in the Ce-doped λiber and . wt.% “l O , . wt.% P O , . wt.% CeO , and . wt.% “u O in the Ce/“u-codoped λiber . ”oth λibers had multimode wave-μuidinμ, which make them useλul λor sensor applications. “ sample oλ standard multimode “l-doped ~ wt.

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% “l O λiber was used in experiments λor comparison. The β-irradiation dosaμe below corresponds to × dose € , × dose € , × dose € , × dose € , × dose € , and . × dose € cm– . Optical transmission spectra oλ λiber samples were measured employinμ the cutback method , usinμ a white liμht source and optical spectrum analyzer OS“ , turned to a nm resolution. Such spectra were recorded beλore and aλter each staμe oλ β-irradiation and at posterior exposure to liμht oλ a He-Ne laser nm or UV lamp λ < nm . The attenuation spectra presented below were obtained aλter recalculatinμ the measured transmissions into loss [d”/m]. In some oλ the λiμures below the diλλerence spectra in terms oλ I“ are provided, which were obtained aλter subtraction oλ the attenuation spectra oλ pristine samples λrom the ones taken aλter a certain dose oλ β-irradiation this allows one straiμhtλorward view on the net€ spectral loss chanμes in the darkened λibers. The transmission dynamics at optical bleachinμ oλ β-darkened λibers by nm liμht was inspected applyinμ λrontal€ detectinμ μeometry where a beam oλ the He-Ne laser was coupled into a λiber sample, while the transmitted liμht was detected usinμ a Si photodetector this permitted detection oλ the chanμes in transmission in situ. The results oλ the measurements are μiven below in terms oλ absorption diλλerence “D at bleachinμ with respect to the initial β-darkened state oλ the λiber. The experiments on optical bleachinμ oλ β-irradiated λibers by UV liμht were as well proceedinμ in situ, where transmission chanμe at lonμ-term exposure to UV liμht was analyzed. “ll experiments were made at room temperature. . . Experimental 2.2. . IA as a result of -irradiation In Figure , we demonstrate a attenuation spectra oλ the Ce-doped black solid curve and Ce/“u-codoped μrey dashed curve λibers beλore irradiation, that is, in their pristine€ state, and b and c the λibers’ cross-sections, obtained at white liμht illumination. Lonμ meters

Figure . a “ttenuation spectra oλ pristine Ce-doped , Ce/“u-codoped , and “l-doped Ce-λree λibers in a VISto-near-IR spectral ranμe and micro-photoμraphs oλ pristine Ce-doped b and Ce/“u-codoped c λibers. Reproduced with permission λrom Kir’yanov et al. [ ]. Copyriμht© , Optical Society oλ “merica .

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

λibers were used in the measurements applyinμ the cutback method, whereas short centimeters pieces oλ λibers«at microscopy. For comparison, spectral loss oλ standard€ “ldoped Ce-λree λiber is presented in Figure a «see red dash-dotted curve . We reveal λrom a that, in both Ce-doped and Ce/“u-codoped λibers, dramatic μrowth oλ absorption occurs toward UV, below ~ nm, which is known to be a shoulder oλ the stronμ absorption bands adherent to Ce +/Ce + ions mostly located in UV [ , ] , and that no such λeature is observed in the reλerence Ce-λree λiber. “lso notice steep loss rise in Ce-doped and Ce/“u-codoped λibers toward IR and a small peak at ~ nm asterisked , the λeatures not observed in case oλ the Ce-λree λiber. Figure shows the trends occurrinμ in the λibers’ attenuation spectra as the result oλ βirradiation at moderate dose . Note that in this case, the measurements were proceedinμ with shorter λiber samples ~a λew cm in virtue oλ stronμ I“, established aλter β-irradiation.

Figure . a “ttenuation spectra oλ Ce-doped , Ce/“u-codoped , and “l-doped cerium-λree λibers, all meas‐ ured aλter β-irradiation with dose × cm– and micro-photoμraphs oλ Ce-doped b and Ce/“u-codoped c λi‐ bers recorded aλter irradiation with this dose. Reproduced with permission λrom Kir’yanov et al. [ ], Copyriμht© , Optical Society oλ “merica .

It is seen that I“ in the Ce-λree λiber is ~two times biμμer than in the Ce-doped and Ce/“ucodoped ones. The other λact is that I“ maxima are located near and nm in these two λibers, whereas the ones in the Ce-λree one«at ~ and ~ nm, that is, in the ranμe most probably attributinμ to well-known nonbridμinμ oxyμen-holes N”OHCs [ ] while the presence oλ other deλect states in it«such as Si-/“l-deλect centers cannot be excluded . Furthermore, it is seen λrom photos b and c that, in the Ce-doped and Ce/“u-codoped λibers, the core and adjacent core-claddinμ areas suλλer darkeninμ aλter β-irradiation, in the λormer, the eλλect beinμ more pronounced. Figure demonstrates that I“ in the Ce-doped a and Ce/“u-codoped b λibers increases monotonously with dose this trend is noticeable λor the – nm ranμe, while λor biμμer wavelenμths it λades. The other detail seen is that λor moderate doses – , I“ is stronμer in the Ce-doped λiber.

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Figure . Main λrames I“ spectra oλ Ce-doped a and Ce/“u-codoped b λibers curves – correspond to doses oλ irradiation in both λiμures beinμ × , × , × , × , × , and . × cm– . Insets averaμe I“-losses measured within the – nm ranμe vs. irradiation dose. Reproduced with permission λrom Kir’yanov et al. [ ]. Copyriμht© , Optical Society oλ “merica .

The two-peaks structure oλ the I“ spectra is apparent at hiμher irradiation doses λor both λibers, with the λirst peak biμμer in maμnitude locatinμ at ~ ± nm and the second one lower in maμnitude «at ~ ± nm compared to the ~ nm peak asterisked in the attenuation spectra oλ pristine λibers in Figure a . To evaluate I“ strenμth in the λibers in λunction oλ βirradiation dose, let us compare the I“ spectra with the attenuation spectra oλ the same λibers beinμ in pristine state reλer to Figure . It is known that attenuation μrowth toward UV is common λor Ce-doped μlass, as stemminμ λrom the transitions inherent to Ce +/Ce + ions. Unλortunately, I“ arisinμ in the UV-reμion, below nm, was undetectable usinμ our experimental equipment. Reμardinμ I“ in the near-IR, note that the spectral transλormations in this reμion are more complex see insets to Figure whose nature is unclear at the moment.

Figure . Main λrames dose dependences oλ I“ λor Ce-doped a and Ce/“u-codoped b λibers blue and red symbols and lines show I“ maμnitudes oλ bands and , obtained aλter deconvolution oλ the spectra shown in Figure . Insets examples oλ deconvolution oλ the data obtained λor the λibers, irradiated with dose spectra are plotted in eV-do‐ main . Reproduced with permission λrom Kir’yanov et al. [ ]. Copyriμht© , Optical Society oλ “merica .

Deconvolution oλ I“ spectra Figure allows a closer view on their two-band structure see insets in Figure a and b . Spectral locations oλ the bands and were λound to be almost independent oλ irradiation dose, λor both λibers they are centered at ~ . and ~ . ± . eV and are measured in halλ-widths at a d” level by ~ . and ~ . ± . eV, respectively. In main λrames oλ Figure , I“«in terms oλ these two peaks’ maμnitudes«is plotted versus irradiation dose these dependences are shown, respectively, by blue band and red band

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

symbols. Fittinμ them within domain oλ smaller doses up to ~ × cm– , linear μrowth oλ I“ in both bands versus dose is revealed see the blue and red lines in the λiμure . The slopes’ values estimated as the result oλ λittinμ were λound to be ~ . ~ . d”/m/cm Cedoped λiber and ~ . ~ . d”/m/cm Ce/“u-codoped λiber , correspondinμly, λor bands and . It deserves mentioninμ that these ratios, on one hand, are almost equal λor both λibers ~ . and, on the other hand, the slopes’ ratios, when compared λor bands and , are vastly equal as well ~ . . Furthermore, at biμμer irradiation doses I“, in both bands and λor either λiber, steadily approaches the plateaus€, marked by black dotted lines in the λiμures. It is interestinμ that I“ in maxima oλ bands and at the plateaus i.e. at doses exceedinμ × cm- has virtually the same maμnitude, λor both λibers. 2.2.2. Bleaching of IA as a result of posterior exposure to 5

nm/UV light

Hereaλter, the λeaturinμ data on optical bleachinμ oλ β-irradiated Ce-doped and Ce/“ucodoped λibers by a low-power He-Ne nm laser and UV mercury lamp are reported.

Figure . Dynamics oλ attenuation decay in terms oλ “D in Ce-doped a and Ce/“u-codoped b λibers under the ac‐ tion oλ nm liμht ~ . mW bleachinμ neμative “D was realized aλter β-irradiation with doses curves , curves , and curves , λor which “D is taken to be zero. c Micro-photoμraphs oλ darkened dose oλ β-irradia‐ tion Ce-doped λiber prior to top and aλter bleachinμ durinμ . h bottom . d Examples oλ the initial nm bleach‐ inμ staμe, zoominμ the dependences shown by curves in a and b , respectively. Reproduced with permission λrom Kir’yanov et al. [ ]. Copyriμht© , Optical Society oλ “merica .

Keepinμ in mind that, I“, a siμnature oλ color centers or deλects in μlass matrix produced at diλλerent kinds oλ irradiation, can be bleached€ by liμht see e.μ. [ – ] , we λound reasonable to check whether such treatment has eλλect in our case. First, we inspected the eλλect oλ weak nm liμht delivered λrom a . mW He-Ne laser. In the experiments, power launched into both λibers was λixed ~ . mW couplinμ eλλiciency

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~ % . In this case, very short pieces … cm oλ β-irradiated λibers were handled, μiven biμ I“, measured by hundreds oλ d”/m reλer to Figures and , beinμ established at β-darkeninμ. The results are shown in Figure . In the leλt part oλ Figure , we show the temporal dynamics oλ chanμes in attenuation oλ the Ce-doped a and Ce/“u-codoped b λibers under the action oλ nm liμht, measured at the same wavelenμth. The eλλect oλ partial bleachinμ oλ β-induced loss the neμative “D is apparent. Note that optical bleachinμ oλ both λibers demonstrates a saturatinμ behavior and that the decay rate is biμμer λor the λiber codoped with “u than λor “u-λree one compare curves – in a and b also notice an almost exponential character oλ bleachinμ when the process μets startinμ see d on the riμht side oλ Figure . The bleachinμ eλλect is clearly demonstrated by the photoμraphs in Figure c , exempliλyinμ the case oλ Ce-doped λiber. It is seen that its initial state beλore β-irradiation was almost restored under the action oλ nm liμht compare the photos in Figure b and Figure c . One would speculate on whether bleachinμ oλ the Ce-doped and Ce/“u-codoped λibers arises solely due to laser-liμht-induced recombination or due to thermally assisted recombination, too, but as λor us, the λormer appears to play a vital role. Figure a and b shows how the bleached main λrames and unbleached insets loss in the Ce-doped and Ce/“u-codoped λibers behave at nm bleachinμ. Note that unbleached remnant loss is biμμer in Ce/“u- than in Ce-doped λiber, that is, codopinμ oλ a Ce-doped λiber with “u results in a similar property oλ lesser susceptibility to exterior inλluence compare with the results on β-irradiation however, in the case oλ bleachinμ this λeature appears to be a disadvantaμe. The results oλ illuminatinμ darkened Ce-doped and Ce/“u-codoped λibers with UV liμht are shown in Figure . In Figure a we exempliλy the spectral dynamics oλ transmission oλ βirradiated at dose Ce/“u-codoped λiber. The photoμraphs in Figure b visualize the result oλ treatment, beinμ almost a λull λadinμ oλ I“ loss. This eλλect can be quantiλied by a shiλt oλ wavelenμth’s transmission, measured at a d” level see μray line in Figure a , λrom near-

Figure . ”leached main λrames and unbleached insets spectral loss in Ce-doped a and Ce/“u-codoped b λibers aλter ~ . mW nm treatment, posterior to β-irradiation with doses curves , curves , and curves . For comparison, curves demonstrate the attenuation spectra oλ pristine λibers. Reproduced with permission λrom Kir’ya‐ nov et al. [ ]. Copyriμht© , Optical Society oλ “merica .

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

IR to VIS. It is seen λrom Figure c , where we demonstrate the results oλ experiments with Ce/“u-codoped black open dots and Ce-doped μray open squares λibers, that it has a similar character λor both λibers.

Figure . a Dynamics oλ attenuation decay in terms oλ transmission oλ Ce/“u-codoped λiber under UV-lamp illumi‐ nation with maximal spectral power @ nm . ”leachinμ was realized in the darkened λiber, posterior to β-irradiation with dose . b Micro-photoμraphs oλ darkened dose oλ β-irradiation Ce/“u-codoped prior to optical bleachinμ with UV-lamp top and aλter continuous bleachinμ durinμ , h bottom . c Examples oλ the spectral transλorma‐ tions durinμ UV-bleachinμ in terms oλ shiλtinμ oλ the λiber’s transmission edμe wavelenμth measured at - d” level the data were obtained λor Ce/“u-codoped open black dots and Ce-doped open μrey squares λibers, preliminary β-irra‐ diated with dose both the data are λitted to the eye by dotted red lines. Reproduced with permission λrom Kir’yanov et al. [ ]. Copyriμht© , Optical Society oλ “merica .

. . Discussion 2. . . Pristine fibers Reμardinμ pristine Ce-doped and Ce/“u-codoped λibers Figure , apart λrom a stronμ μrowth oλ absorption seen at shorter VIS to UV wavelenμths apparently connected with the presence oλ Ce in valences Ce +/Ce + [ , ] , the other two points deserve mentioninμ, beinμ i monotonous μrowth oλ loss toward IR in both λibers oλ not clear oriμin but inherent to Ce dopinμ since such trend is absent in the reλerence Ce λree λiber and ii a distinct peak at ~ nm ~ . eV in the absorption spectra oλ both λibers but absent in the Ce λree one . We suppose that this peak has the same oriμin as band risen at β-irradiation and located at ~ . eV see Figure . This λeature has not been reported λor bulk Ce-doped silica but is λrequently observed in Ce-doped λibers subjected to ionizinμ radiations [ , ]. It can be related to quite stable Ce +h+ centers, or alternatively while hypothetically, to Ce +e− centers existence oλ which

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was not documented , but apparently not to sole Ce ions beinμ in either trivalent or tetravalent state. “s λor us, a more realistic cause λor the existence oλ Ce +h+ or/and Ce +e− deλect centers in pristine λibers, attributable by the nm peak, can be ionization, that is, μeneration oλ electrons − + e and holes h , at the λiber preλorm’s collapse staμe [ ] or durinμ the λiber’s drawinμ with posterior coverinμ by acrylic outer claddinμ when«in both situations«stronμ UV liμht is produced, with a result beinμ a trappinμ oλ λree carriers by Ce +/Ce + species. 2. .2. -irradiated fibers Consider in more details the results oλ β-irradiation oλ Ce-doped and Ce/“u-codoped λibers Figures – . The processes, involved at irradiatinμ the λibers with the result beinμ rise λollowed by saturation oλ I“, described by the stretched-exponent€ law [ , , ] , comprise i creatinμ oλ secondary carriers holes h+ and electrons e− in the core-μlass matrix by β primary electrons and their trappinμ on such μlass imperλections as Ce ions Ce +/Ce + , nonbridμinμ oxyμen centers, other centers associated with “l and P, and oxyμen vacancies ii direct h+…e− recombination annihilation iii thermally or/and radiatively activated recom‐ bination between the centers or deλects that have arisen durinμ and aλter β-irradiation. Concerninμ the role oλ Ce-dopinμ, we assume that I“ is produced via irradiation-induced reactions Ce ++h+→Ce +h+ →?Ce + and Ce ++e−→ ?Ce +e− →Ce + [ – ], implyinμ Ce was in valences +/ + in pristine λibers or/and beinμ μenerated via irradiation. Note that determina‐ tion oλ relative contents oλ Ce +/Ce + ions in the pristine state is hard and that at low Ce dopinμ, mainly λluorescinμ Ce + are λormed in the core-μlass, while at hiμher overall Ce concentration both Ce + and Ce + nonλluorescinμ ions can be present. Unλortunately, the absorption spectra oλ μlasses containinμ both Ce +/Ce + ions have the λeaturinμ bands within a – nm UV ranμe not detectable by our spectral equipment so any arμuinμ about Ce +↔Ce + transλor‐ mations λor this ranμe is impossible. In the meantime, the absorption bands oλ Ce +h+ and Ce +e − deλect centers are expectedly located in VIS see above , on one hand, and, on the other hand, the detected spectral chanμes at β-irradiation occur in VIS, too band thus, λormation oλ metastable centers Ce +h+/Ce +e− as its result is a worthy proposal. Furthermore, I“ bands ~ . eV and ~ . eV see Figure have been undoubtedly separated see above. The λirst oλ them, in Ce-doped and Ce/“u-codoped λibers, has seeminμly the same oriμin as the one in the Ce-λree λiber see Figure , that is, it most probably belonμs to one, most simply orμanized, type oλ the two N”OHCs centers, inherent to silica. The other would stem λrom Ce dopinμ it is seen λrom Figure that such band does not exist in the reλerence Ce-λree λiber. However, the irradiated Ce-λree λiber demonstrates ~ nm band, probably attributinμ the other type oλ N”OHCs [ ], absent in both Ce-doped λibers subjected to irradiation compare spectra – shown in Figure . The λact that the dose dependences oλ I“ Fiμure have diλλerent characters λor the λibers points on diλλerent nature oλ the centers represented by bands and . Thereλore, our hypothesis that ~ . eV band stems λrom N”OHCs and that ~ . eV one is associated with a Ce-related center Ce +h+/Ce +e− seems to be relevant. In our case alumino-silicate core μlass oλ Ce-doped and Ce/“u-codoped λibers , such point€ deλects as “l-E’ and “l-oxyμen-deλicient centers can be also created at trappinμ secondary

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

electrons and holes born at β-irradiation phosphorous P presented in small amount plays a little eλλect . Thus, the processes rouμhly schematized as Ce +↔Ce + seem to be a sole way to address the spectral transλormations seen λrom Fiμures – to happen via the λormation in the Ce- and Ce/ “u-doped λibers oλ metastable states Ce +h+/Ce +e−. Furthermore, it deserves mentioninμ that overall susceptibility to β-irradiation overall I“ loss oλ Ce-doped λiber is hiμher than oλ Ce/“u-codoped one. This may siμniλy that the core μlass containinμ μold is more stable than that solely doped with Ce. On the other hand, deviations in the experimental data λor kinetics oλ I“ versus β-irradiation dose λor the λibers reλer to I“ spectra in Figure and to dose dependences in Figure are more pronounced in the λormer than in the latter λiber. “ possible explanation λor this can be that codopinμ with “u μives rise to the core-μlass system more ordered. This property seems to have impact λor establishinμ almost the same path kinetics oλ deλect centers’ λormation as compared with other λactors involved in such oλ type λibers. 2. . . Optically bleached fibers Let us discuss now the eλλect oλ partial bleachinμ oλ β-irradiated Ce-doped and Ce/“u-codoped λibers under the action oλ low-power VIS/UV liμht see Fiμures – . Whereas a doubtless conclusion on its nature is hard, some discourse about the matters involved can be made. The processes responsible λor recombination oλ radiation-induced deλects or color centers, seen as I“ λadinμ bleachinμ oλ darkened λibers, can be oλ thermally and/or optically induced oriμin. ”leachinμ, with its result beinμ decreasinμ I“ versus time, seems to be an example oλ mainly optically induced recombination oλ both types oλ centers, N”OHCs and Ce-related Ce +h+ assumed to be represented by bands and , respectively ones. “s seen λrom Figure d and Figure c , I“ decreases almost exponentially at the beμinninμ oλ bleachinμ. However, within the whole interval oλ optical bleachinμ, I“ in bands and is seen to λade in terms oλ neμative “D at nm illumination, see Figure a, b , as well as in terms oλ shiλtinμ the transmission edμe to shorter wavelenμth, at exposure the λibers to UV liμht, see Figure a, c , which obeys a stretched exponent€ law [ ]. “n explanation λor this behavior can be not only complexity oλ the mechanisms involved at optical bleachinμ but also a λact oλ limited penetration€ oλ bleachinμ liμht into a λiber sample especially in the case oλ nm bleachinμ . Concerninμ the essence oλ I“ at optical bleachinμ, we can, at the current staμe oλ our knowl‐ edμe, propose them only tentatively. Iλ our attribution oλ I“ bands and as siμnatures€ oλ N”OHCs and Ce-related Ce +h+ centers is correct, then these centers, λormed at trappinμ λree holes, should be breakinμ via the holes’ detrappinμ and annihilatinμ with λree electrons born at interaction with VIS/UV liμht. Weak intensity oλ bleachinμ liμht is μuessed to produce mainly extra electrons rather than holes in the core-μlass, leadinμ to dominance oλ the processes relatinμ to the hole-trapped centers, such as N”OHC ~ . eV band and Ce +h+ ones ~ . eV band . Note that a stronμ candidate to be in-charμe€ oλ production oλ e− at the UV/VIS excitation may be Ce + ions themselves [ ].

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Comparison oλ the bleachinμ eλλect in Ce-doped without “u codopinμ and Ce/“u-codoped λibers show that it is less expressed in the latter than in the λormer, which is probably related to lower susceptibility to exterior inλluence oλ Ce/“u-codoped λiber a consequence oλ its more ordered μlass network, already noticed .

. Electron irradiation versus PD of Yb-doped germano-alumino-silicate fibers: The effects comparison Yb +-doped silica λibers YFs with diλλerent core-μlass hosts codoped with “l, Ge, or P have been oλ considerable interest durinμ the past decades as extremely eλλective media λor λiber lasers λor the spectral reμion . – . μm, when pumped at . – . μm wavelenμths. “ variety oλ diode-pumpinμ conλiμurations core and claddinμ and pump wavelenμths were examined so λar, resultinμ in recoμnition oλ optimal arranμements λor multi-watt release λrom YF-based lasers with hiμh optical eλλiciency ~ – % and perλect beam quality [ , ]. However, in spite oλ a remarkable proμress in the λield, there remain obstacles that limit the perλormance oλ YFbased lasers, one oλ them beinμ PD [ ], that is, lonμ-term minutes to hours deμradation oλ laser power, measured by units to tens %. This hardly mitiμated disadvantaμe becomes notable when dealinμ with a laser based on heavily doped YF where a hiμh Yb + population inversion is created, either at hiμh-power continuous-wave or moderate-power pulsed lasinμ. “ number oλ studies were aimed to understand the PD phenomenon which however remained unclear, althouμh a λew hypotheses have been proposed λor its explanation [ – ]. On the other hand, a λew studies aiminμ the characterization oλ susceptibility oλ YFs under such irradiations as X-rays, γ-quanta, and UV have been reported [ – ]. The main motivation was inspection oλ YF-resistance to harmλul environments. In many cases, the excess-loss spectra induced in YFs resemble the ones, characteristic λor PD at resonant pumpinμ into Yb + resonant-absorption band, the λact undoubtedly deservinμ attention. Here, the results oλ two sets oλ experiments, where susceptibility oλ YFs with similar μermanoalumino-silicate μlass-cores, doped with Yb in diλλerent concentrations to irradiation by a beam oλ β-electrons and to resonant into Yb + resonant band optical pumpinμ, are presented. In both circumstances, qualitatively similar trends are revealed, beinμ stronμ and monotonous chanμe in attenuation in VIS darkeninμ , accompanied by more complex transλormations within the resonant absorption band oλ Yb + ions, either upon dose the case oλ β-electron irradiation , or exposinμ time the case oλ optical pumpinμ at nm . ”elow, we compare and discuss the experimental results and attempt to explain them. . . Fiber samples and experimental arrangement The YFs inspected in these experiments were drawn λrom μermano-alumino-silicate μlass preλorms λabricated usinμ the conventional€ MCVD/SD route. The attenuation spectra oλ the λibers beinμ in pristine as-received state are demonstrated in Figure a .

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

Figure . a “ttenuation small-siμnal absorption spectra oλ λibers with low YF- , intermediate YF- , and hiμh YF- Yb + contents curves , , and , respectively. b Fluorescence spectra oλ the λibers at resonant nm excitation pump power« mW . Labelinμ oλ curves , , and is the same as in a and b . Inset in b shows cooperative€ λluorescence in VIS. Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Scientiλic Research Publish‐ inμ Inc .

The concentrations oλ Yb + ions in the λibers diλλered by more than an order oλ maμnitude, so certain diλλerences were expected aλter their exposure to β-electron irradiation hereaλter in this paraμraph«e-irradiation and to optical pumpinμ hereaλter«OP at nm wavelenμth . The λibers, havinμ the lowest, the intermediate, and the hiμhest Yb + dopinμ level, are reλerred λurther to as YF- , YF-2, and YF- , respectively. The essences oλ experiments on e-irradiation oλ the YFs were completely the same as at irradiatinμ the Ce-doped λibers Paraμraph . The indices  ,€  ,€ and  € label below the doses × , × , and × cm– , respectively. Experiments on OP at nm were made in a similar way as described in Reλ. [ ]. YF samples were pumped usinμ a standard mW nm laser diode LD . The pump liμht was launched λrom LD to an YF sample under study throuμh a splice. The end oλ the latter was spliced to a piece oλ SMF- λiber that was, in turn, connected to an OS“ λor the transmission spectra’ measurements. In these experiments, we handled short a λew cm pieces oλ YFs to ensure nolasinμ conditions and neμliμible contribution oλ ampliλied spontaneous emission oλ Yb +. The optical transmission spectra oλ the YF samples were obtained usinμ a white liμht source with a λiber output and the OS“, turned to a nm resolution. These spectra were recorded over the spectral ranμe – nm, where the most interestinμ spectral transλormations occur as the result oλ e-irradiation/OP. The output oλ the white liμht source was connected to a λiber set containinμ an YF sample pristine or subjected to e-irradiation/OP , while its attenuation was measured usinμ the OS“. The attenuation spectra were recorded beλore and aλter each staμe oλ e-irradiation doses or OP at nm pumpinμ times . Lenμths oλ the YFs were chosen to be short enouμh, λrom < cm YF- to tens cm YF- , to avoid spectral noise artiλacts. In some oλ the λiμures below, the diλλerence I“ spectra are demonstrated which were obtained aλter subtractinμ the attenuation spectra oλ pristine samples λrom the ones taken aλter certain dose/time oλ e-irradiation/OP. This allows insiμht to net€ spectral loss, established aλter darkeninμ oλ either type. “ll the spectra presented beneath have been obtained aλter recalcu‐ latinμ transmission coeλλicients in loss [d”/cm]. We also measured the λibers’ λluorescence

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Radiation Effects in Materials

spectra and λluorescence kinetics oλ Yb + ions beλore and aλter e-irradiation/OP, applyinμ the lateral€ μeometry [ ]. We used the same OS“ λor the λluorescence spectra measurements and a Ge photodetector PD and oscilloscope λor the λluorescence-decay measurements. In the last case, LD power was modulated by a driver controlled by a λunction μenerator to achieve square-shaped pulses with sharp rise and λall edμes. The time resolution oλ the setup was μs. “ll the experiments were made at room temperature. . . Experimental .2. . E-irradiation The attenuation spectra oλ samples YF- and YF- , havinμ correspondinμly the hiμhest and lowest Yb + concentrations, obtained aλter diλλerent doses oλ e-irradiation, alonμ with the attenuation spectra oλ the samples in a pristine dose  € state are shown in Figure a, b .

Figure . “ttenuation spectra oλ samples YF- a and YF- b . The data are λor e-irradiation doses increased λrom  € pristine samples throuμh  € and  €– €. Insets show the diλλerence spectra obtained aλter subtraction oλ the spectra oλ pristine samples λrom the ones aλter e-irradiation oλ the samples. Dashed lines show the positions oλ wavelenμths λor which the data in Figure are built. Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Scientiλic Research Publishinμ Inc .

First, a notable increase oλ backμround loss in VIS with increasinμ e-irradiation dose is revealed see main λrames oλ Figure . “lso notice a speciλic spectral character oλ this loss λor both λibers, viz. a drastic rise oλ loss-maμnitude toward shorter wavelenμths. This is a well-known λor Yb +-λree silica λibers’ trend in experiments on various kinds oλ irradiations. “t the same time, apparent diλλerences are seen in maμnitude oλ e-irradiation-induced loss in these two λibers, that is, a hiμher deμree oλ darkeninμ in YF- than in YF- . For YF- , intermediate in Yb + dopinμ level, the eλλect oλ e-irradiation is intermediate, as compared with YF- and YF- .] Second, detectable but less pronounced spectral transλormations are revealed λor the resonantabsorption band oλ Yb + – nm see insets to Figure , where the diλλerence spectra

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

are shown, obtained as explained above. Very weak in YF- Fiμure b , the spectral trans‐ λormations are noticeable in YF- Fiμure a . These chanμes seem to be a result oλ some process, associated with e-irradiation oλ the λibers, which aλλects concentration oλ Yb + ions. More details are seen in Figure where we plot the results λor samples YF- a and YF- b , taken λor all doses. Figure a, b demonstrates how attenuation within the resonantabsorption oλ Yb + ions peaks at and nm, see also Figure a chanμes throuμhout eirradiation see curve λor the nm peak and curve λor the nm peak , respectively. “ decrease λollowed by an increase in the maμnitude oλ small-siμnal absorption arises in both peaks with dose increasinμ in YF- heavier doped with Yb + this trend is, in contrast, less expressed in YF- lower doped with Yb + . For comparison, we plot in Figure the chanμes in attenuation oλ YF- c and YF- d λibers in VIS, where backμround nonresonant losses arise as the result oλ e-irradiation. Here we limit ourselves by the data, counted λor curve and curve nm. It is seen that backμround loss steadily μrows with dose, a common eλλect λor silica λibers. Note that the rate oλ μrowth is hiμher in YF- than in YF- . Furthermore, an initial level oλ backμround loss in pristine YF correlates with initial content oλ Yb + ions.

Figure . Dose dependences oλ attenuation in resonant-absorption Yb + peaks centered at curves and curves nm top panels and in VIS, λor wavelenμths curves and curves nm bottom panels . The data are λor samples YF- a, c and YF- b, d . Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Scien‐ tiλic Research Publishinμ Inc .

Figure a and b μathers the experimental data obtained usinμ all λibers, YF- , YF , and YF- . From Figure a , it is seen that a monotonous increase oλ nonresonant loss in VIS darkeninμ , exampled by wavelenμths and nm, with increasinμ Yb + concentration

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Radiation Effects in Materials

the latter is proportional to YF small-siμnal absorption at nm. This demonstrates that the presence oλ Yb + dopants μain their deμradation at e-irradiation. Here we show the results obtained at dose  € only, because λor other doses the dependences are similar, μiven by a smooth dependence oλ induced loss in VIS versus e-irradiation dose see Figure c, d . From Figure b , it is seen that the lowest levels to which the values oλ absorption in the nm peak approach throuμhout e-irradiation minima oλ curves in Figure decrease with increasinμ Yb + content a similar trend is observed λor the other peak oλ Yb +, at nm . This λact seems to be in λavor oλ that initial concentration oλ Yb + ions in pristine samples substan‐ tially decreases as a result oλ e-irradiation, at the primary staμe. However, at the λollowinμ staμes, Yb + concentrations are re-established on levels comparable with those in pristine YFs reλer to Figure a . [The remainder oλ Figure c, d provides the data, obtained in the experiments on OP oλ the YFs, reported below.]

Figure . The results oλ experiments with λibers YF- , YF- , and YF- , which were obtained λor diλλerent e-irradiation doses a, b and OP times c, d . The data are λor the resonant-absorption peaks at and nm λilled and empty asterisks b, d and λor the VIS reμion, exampled by wavelenμths nm crossed squares and nm crossed cir‐ cles a, c . Dotted lines are λor visual purposes only. Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Scientiλic Research Publishinμ Inc .

.2.2. PD at OP We report here the results oλ OP experiments λor sample YF- mainly see Figures – , havinμ the biμμest content oλ Yb + ions. Then, we summarize all the results, obtained λor YF- , YF- , and YF- λibers, in Figure c, d .

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

Figure . “ttenuation small-siμnal absorption spectra oλ λiber sample YF- aλter OP @ nm. The data are λor a pristine sample curve  min€ and λor photo darkened samples curves and , obtained aλter and min oλ OP, respectively . Dashed lines show the positions oλ wavelenμths λor which the data in Figure are built. Repro‐ duced with permission λrom Kir’yanov [ ]. Copyriμht© , Scientiλic Research Publishinμ Inc .

Figure . Dose dependences oλ attenuation in resonant-absorption Yb + peaks centered at curve and curve nm a and in VIS, λor wavelenμths curve and curve nm b . The data are λor sample YF- . Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Scientiλic Research Publishinμ Inc .

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Figure . Diλλerence attenuation spectra aλter dose  € oλ e-irradiation curve and aλter h oλ OP at nm pump power is mW curve curve is the diλλerence oλ spectra and . The data are λor sample YF- . Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Scientiλic Research Publishinμ Inc .

Fiμure shows the attenuation spectra oλ sample YF- lenμth, . cm aλter and min. oλ OP. The LD power was λixed in these experiments at mW, the hiμhest in our circum‐ stances level oλ Yb + ions inversion. For comparison, the attenuation spectrum oλ pristine min sample YF- is shown in Figure , too. Once compared with the attenuation spectra aλter e-irradiation reλer to Figure a , these spectra are seen to be similar. That is, a substantial increase oλ backμround loss is observed in VIS with increasinμ OP-time the PD eλλect . Note that the spectral siμnature€ oλ PD resembles the one aλter e-darkeninμ see Figure . In Figure a , we demonstrate the results oλ the experiments with sample YF- , obtained at increasinμ OP time. Their representation is similar to the one used at the description oλ experiments on e-irradiation see Figure a . From Figure a , it is seen how attenuations in the two absorption peaks oλ Yb + ions at and nm chanμe throuμhout OP see curves and , respectively. The time dependence oλ OP-induced chanμes at nm resembles the dose dependence at e-irradiation oλ sample YF- . However, curve in Figure a has asymmetric€ shape versus OP time, diλλerinμ λrom symmetric€ shape oλ the dose depend‐ ence at e-irradiation μiven by curve in Figure a . Furthermore, the time dependence oλ OP-induced chanμes at nm, see curve in Figure a , is very weak, beinμ completely diλλerent λrom curve in Figure a e-irradiation . Thereλore, we can propose that diλλerent mechanisms, responsible λor the induced chanμes in the resonant-absorption band oλ Yb + at and nm, stand behind these two e-irradiation and OP treatments oλ the λibers. In Figure b , we demonstrate the results oλ spectral transλormations arisinμ in YF- in VIS, at OP. “μain, we provide in Figure b , the data λor a couple oλ wavelenμths, curves and curves nm, as most representative. In contrast to the dose dependences at eirradiation, lonμ-term OP at nm results in completely diλλerent dynamics oλ backμround loss in time. Indeed, it is essentially nonlinear versus time there is a short timinμ interval in the beμinninμ λew minutes where PD increases dramatically, while aλterward tens oλ minutes it slows down and tends to saturate.

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

Figure allows one to compare the attenuation spectra λor YF- suλλered dose  € oλ eirradiation curve and h oλ OP curve . The spectra look qualitatively similar, which may tell that the mechanisms involved are similar in these two circumstances. “t the same time, iλ one spectrum is subtracted λrom another, the result curve in Figure brinμs some news. That is, apart λrom the diλλerence presented in VIS in backμround loss , there is a λeature in the Yb + resonant band thouμh no deviation λrom plain€ behavior oλ curve is seen near nm peak oλ Yb +, there is a well-deλined neμative nm peak it is marked by a dotted rinμ . This detail seems to be important as it liμhtens nonhomoμeneity within the Yb + resonantabsorption band near nm, present at OP but not«at e-irradiation. This detail becomes expressed more when one analyzes the data obtained at PD oλ the other λibers, YF- and YF- see Figure . In this λiμure, where we plot the diλλerence spectra obtained λor these λibers, analoμous but clearer seen detail appears exactly within the nm peak oλ Yb + ions it is marked by a dotted rinμ in a and b .

Figure . Diλλerence loss spectra oλ YFmission λrom Kir’yanov [ ]. Copyriμht©

Let us return to Figure

a and YF- b , obtained aλter h oλ OP at , Scientiλic Research Publishinμ Inc .

nm. Reproduced with per‐

c, d , where we μather the results on OP λor all YF samples.

In contrast to the results on e-irradiation Figure a, b , one can reveal λirst nonlinear μrowth oλ backμround loss at and nm with increasinμ Yb + concentration Figure c . “pparently, this behavior is diλλerent λrom linear μrowth oλ backμround loss at e-irradiation Figure a . Second, it is seen that, instead oλ a linear decrease oλ the resonant peaks at and nm with dose occurrinμ at primary staμes oλ e-irradiation«see Figure b , a nonlinear law is obeyed by a decrease oλ the resonant peak at nm while almost no chanμe happens with the peak at nm Figure d . Thus, the situation with OP-induced spectral transλormations in the YFs is complex and curious at λirst μlance. The nm peak is stronμly aλλected by OP, not the nm one. This can be explained by the presence in the λibers oλ some other centers than Yb + dopants, but closely related to them and spectrally matchinμ them near nm. Moreover, partial weiμht oλ such centers in YF-core is expected to increase with increasinμ Yb + ions concentration. The nonlinear behavior oλ the nonresonant backμround loss versus OP time, discussed earlier see Figure b , seems to be a related phenomenon.

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.2. . What’s about fluorescence? The λluorescence spectra obtained usinμ pristine YF- , YF- , and YF- λibers at nm pumpinμ are shown in Figure b . “ll these are similar in appearance and their intensities are propor‐ tional to Yb + ions concentrations in the λibers The measurements were made at the same conditions and at the same pumps. We also measured the λluorescence spectra oλ the YFs aλter irradiation by an electron beam and aλter lonμ-term OP at nm, but almost no qualitative spectral chanμes were captured in the Yb + λluorescence band so we don’t provide them here. We could only notice a small decrease in the λluorescence power as the result oλ the treatment, but this trend could not be quantiλied. Furthermore, it was λound that the characteristic Yb + λluorescence decay time sliμhtly decreases in the set oλ pristine YFs. This is a result oλ the presence oλ two exponents in the λluorescence kinetics, measured by ~ . and ~ . … . ms. Note that insiμniλicant μrowth oλ the latter contribution was detected λor the λiber with the hiμhest Yb + content YF- see also Reλ. [ – ]. However, the time constants obtained at λittinμ were nonaλλected neither by e-irradiation nor by lonμ-term OP. Concludinμ, we can reveal that none, or very insiμniλicant, chanμes occurred in the YFs in the sense oλ Yb + λluorescence. . . Discussion Summarizinμ all the data, we notice that either at e-irradiation or at resonant OP substantial and complex but diλλerent in appearance chanμes arise within the resonant absorption band oλ Yb + ions reversible bleachinμ€ , while monotonous μrowth oλ nonresonant backμround loss is observed in VIS darkeninμ€ . Furthermore, these trends are revealed to stem λrom the chanμes in concentrations oλ Yb + ions and, seeminμly, oλ other centers, closely related to them and spectrally matchinμ them near nm. This is the main news oλ this study. “ μeneral consequence oλ the experiments on e-irradiation, rise oλ backμround nonresonant loss in YFs in VIS see Figure c, d , is not surprisinμ. This loss correlates spectrally with the excess loss arisinμ in optical λibers at other types oλ irradiation X-rays, γ-quanta, UV [ – ] . Some other aspects are as λollows .

“ monotonic increase oλ the backμround loss in VIS darkeninμ with increasinμ Yb + content in the YFs, which demonstrates that the presence oλ Yb + dopants leads to a hiμher deμree oλ the λibers’ deμradation at e-irradiation Figure a .

.

“ notable decrease λollowed by equally notable increase arisinμ in the resonant-absorption peaks oλ Yb + at and nm with increasinμ e-irradiation dose Figure a, b , the eλλect also dependent on Yb + concentration Figure b . Thus, the presence oλ Yb + dopants in the λibers results in a more pronounceable deμra‐ dation at e-irradiation, with a probable reason beinμ that Yb + ions are powerλul sources oλ secondary carriers electrons and holes born at e-irradiation. That is, the chanμes within the resonant-absorption band oλ Yb + may stem λrom excitation oλ inner-shell f electrons oλ Yb + and their valence transλormation throuμh the charμe-transλer CT processes direct and reversed , sketched by the λollowinμ reactions [ ] e- + Yb + → Yb2+; e+ + Yb2+ → Yb +,

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

where e– and e+ stand λor secondary irradiation induced electrons and holes, and Yb + is the notation λor Yb ions in + valence state. In turn, the presence in the λibers oλ secondary carriers as the result oλ e-irradiation can produce such deλects as oxyμen-deλicit center ODC and N”OH centers [ ]. These centers are known to be responsible λor the wide excess-loss spectral bands similar to the ones produced in the darkened λibers Fig‐ ures and . Qualitatively similar observations can be made reμardinμ the spectral transλormations in the YFs as the result oλ OP at nm reλer to Figure c, d and Figures – . “nalo‐ μously, the λollowinμ trends are drawn .

”ackμround loss in VIS substantially μrows at lonμ-term OP see Figures and b while its character is typical λor PD in YFs [ – ]. However, an increase oλ this loss in VIS with increasinμ small-siμnal absorption has, in contrast to e-irradiation, a nonlinear law Figure c , thus revealinμ an almost quadratic dependence versus Yb + concentration.

.

The dependences oλ resonant absorption, measured in the peaks oλ Yb + at and nm upon OP time, have essentially diλλerent characters Figure a . Iλ the absorption coeλλicient in the nm peak chanμes by a law similar to the one at e-irradiation, the absorption coeλλicient in the nm peak is virtually constant throuμhout lonμ-term OP. The concentration dependences shown in Figure d tell us more the chanμes in these peaks with increasinμ content oλ Yb + ions are also diλλerent. We cannot interpret these details in terms oλ simple concentration dependences in reμard to Yb + ions. Otherwise, an assumption can be made instead that the chanμes in the nm peak are related to the + chanμes in concentration oλ some others than Yb ions centers but spectrally matchinμ them in the nm peak.

.

The spectral siμnature oλ the latter is seen λrom Figures and where the diλλerence attenuation spectra aλter OP are demonstrated. One can see λrom these λiμures that the PD eλλect μrowth oλ nonresonant loss in VIS is accompanied by bleachinμ oλ the resonant peak at nm, whereas none happens with the peak at nm. Note that a similar λeature was reported earlier λor the other type oλ YF, λabricated by the DND method [ ].

The observations – , when μathered toμether, tell us that PD in the YFs at hiμh-power, lonμterm OP at nm arises amonμ the centers concentration oλ which is a nonlinear almost quadratic λunction oλ Yb + ions concentration. These are most probably the centers composed oλ couples oλ Yb + ions pairs , or aμμlomerates oλ the latter. Furthermore, similar reactions e+ Ybp + → Ybp2+ e+ + Ybp2+ → Ybp + see above can be proposed to address these transλormations at OP, where index p stands to show that a pair oλ Yb + ions is involved in the processes and notations e– and e+ are used λor an electron and a hole, λree or trapped by the nearest liμand, say oxyμen. Such reactions can μo at the assistance oλ CT-processes between ion pairs where both constituents are in the excited state. Hence, the spectrally wide backμround loss PD in the λibers see Figures and can be produced Ybp + and oλ e–/e+-related centers say, ODCs and N”OHCs at OP, like this takes place at e-irradiation.

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It is currently accepted that PD occurs amonμ clusters oλ Yb + ions obviously, pairs are their kind . However, a novelty λound here is the spectral λeature, occurrinμ at OP see dotted rinμs in Figures and but not«at e-irradiation. There are evidences λor that PD can be itselλ associated with nonbindinμ oxyμen near surλaces oλ Yb/“l clusters that can be λormed in alumino-silicate μlass our case . The nonbindinμ oxyμen oriμinates λrom Yb + substitutinμ Si + sites. When subjectinμ a YF to nm OP, the excess enerμy is radiated as phonons, causinμ a lone electron oλ a nonbindinμ oxyμen atom to shiλt to a nearest neiμhbor nonbindinμ oxyμen atom with creation oλ a hole and a pair oλ lone electrons, which results in a Coulomb λield between the oxyμen atoms to λorm an unstable color€ center. Conversion oλ such an unstable center to a semistable center requires shiλtinμ oλ one electron oλ the lone electron pair to a nearest neiμhbor site. “s a result oλ this, the λormation oλ Yb-related ODC can happen. On the other hand, PD in alumino-silicate YFs may take place via breakinμ oλ ODC, which μives rise to release oλ λree electrons. The released electrons may be trapped at “l or Yb sites to λorm a color center resultinμ in PD. These hypotheses can serve as the arμuments, brinμinμ more clarity in understandinμ the similarity oλ the spectral transλormations in YFs at e-irradiation creation oλ secondary€ carriers by βelectrons and at OP creation oλ carriers and color centers by pump-liμht .

. Effect of electron irradiation upon optical properties of Bi-doped silica fibers ”i-doped silica λibers with core-μlass codoped with “l, Ge, or P are currently oλ increasinμ interest, beinμ a promisinμ active medium λor ampliλyinμ and lasinμ in the spectral ranμe . – . μm see e.μ. [ – ] . In spite oλ remarkable success in the λield, there remain certain obstacles λor λurther improvements oλ ”i λiber lasers and ampliλiers because the main problem is lack oλ clarity in the nature oλ ”i active€ centers Further«”“Cs in silica μlass. Thus, any research aiminμ to recover the essences oλ ”“Cs would have value. ”elow we hiμhliμht the eλλect oλ irradiation oλ ”i-doped μermano- and alumino-silicate λibers by a beam oλ λree electrons oλ hiμh enerμy. The main result oλ the treatment was λound to be decrement bleachinμ€ /increment rise oλ resonant absorption in the characteristic peaks, beinμ ascribed to ”“Cs in ”i-doped μermano-silicate/alumino-silicate λibers. Note that analoμous trends were reported λor similar λibers and μlasses under the action oλ UV laser pulses and γ-quanta [ , ] . Given that the other optical properties oλ the λibers under scope, such as ”“Cs λluorescence spectra and liλetimes, were λound to be weakly aλλected by electron irradiation, the chanμes in the absorption spectra should be associated with the chanμes in ”“Cs concentration, as λirmly justiλied in our study. . . Fiber samples and experimental arrangement The ”i-doped silica λibers were drawn λrom Ge and “l codoped silicate-μlass preλorms, λabricated applyinμ the MCVD/SD technique. Core radii oλ the λibers were measured to be in the … μm ranμe. The representative attenuation spectra oλ pristine as-received ”i-doped

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

μermano- and alumino-silicate λibers, havinμ comparable contents oλ ”“Cs, are shown in Figure . Hereaλter, the emission-active ”“Cs are reλerred to as ”i Ge,Si and ”i “l , respec‐ tively, in these two types oλ λiber. Impact oλ electron irradiation on the basic characteristics oλ the λibers, reλerred to λurther as Bi- , Bi-2, and Bi- μermano-silicate and Bi- aluminosilicate , is addressed subsequently.

Figure . “ttenuation spectra oλ typical ”i-doped μermano-silicate curve and alumino-silicate curve silica λi‐ bers. “rrow shows the pump wavelenμth nm used in the experiments on λluorescence spectra and liλetimes measurements. Dashed lines show schematically a trend oλ the backμround loss to μrow toward shorter wavelenμths. Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Optical Society oλ “merica .

Electron irradiation oλ ”i- …”i- λibers was proceedinμ in the conditions, described in Introduction the indices  ,€  ,€ and  € label to doses × , × , and × cm– , respectively. The technique applied to reveal the spectral transλormations in attenuation oλ the ”i-doped λibers as the result oλ irradiation was completely the same as described in Paraμraphs and and is not repeated here. When measurinμ ”i-related λluorescence, we utilized the same LD pump wavelenμth, nm λor excitation. “s seen λrom Figure , the pump wavelenμth was on the Stokes tail oλ the – nm absorption band oλ ”“Cs in ”i-doped μermano-silicate λiber and, correspondinμly, on the anti-Stokes slope oλ the absorption band centered at nm oλ ”“Cs in ”i-doped alumino-silicate λiber. We applied in the ”“Cs λluorescence measurements the lateral detectinμ μeometry, when it was collected λrom the surλace oλ a ”idoped λiber sample the same OS“ and a Ge PD were handled to proceed the λluorescence measurements. . . Experimental The experimental results are presented by Figures – . The attenuation spectra oλ ”i-doped μermano-silicate λiber sample ”i- subjected to electron irradiation with doses  € and  € are shown in Figure a alonμ with the attenuation spectrum oλ a pristine dose  € λiber oλ the same type. “ stronμ irradiation-induced bleachinμ eλλect can be revealed λrom the λiμure, seen as drop oλ maμnitude oλ the absorption peaks labeled  € the – nm band and  € the

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Radiation Effects in Materials

Figure . a “ttenuation spectra oλ ”i-doped μermano-silicate λiber sample ”i- obtained beλore dose  € and aλter doses  € and  € irradiation. The spectral area, comprisinμ the resonant-absorption peaks  € and  € which attrib‐ ute ”i Ge,Si centers in the host μlass, is shown b Insiμht to the spectral area oλ peak  € in a vaster scale. Repro‐ duced with permission λrom Kir’yanov [ ]. Copyriμht© , Optical Society oλ “merica .

Figure . “ttenuation spectra oλ ”i-doped μermano-silicate λibers ”i- curves and and ”i- curves and , ob‐ tained beλore dose  € and aλter dose  € electron irradiation. [The spectral area λor the peak  € is zoomed.] Re‐ produced with permission λrom Kir’yanov [ ]. Copyriμht© , Optical Society oλ “merica .

– nm band . It is accompanied by an increase oλ backμround loss at shorter wave‐ lenμths reλer to the leλt side oλ Figure a , a well-known λeature in experiments on inλluence oλ various type oλ irradiations on optical properties oλ Ge-doped silica λibers see e.μ. Reλs. [ – ] . Unλortunately, such a drastic μrowth oλ backμround loss did not allow us to make wellresolved measurements oλ the irradiation-induced transλormations oλ ”“Cs band peaked at ~ nm see Figure , so we inspected mostly the chanμes in peaks  € and  €. “lso notice that almost no chanμes arise in the attenuation peak at nm, which corresponds to the cutoλλ wavelenμth this and other ”i-doped μermano-silicate λiber samples were drawn to provide sinμle-mode propaμation λor wavelenμths > nm.

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

Figure . Dose dependences oλ attenuation oλ the resonant-absorption peaks  € ~ nm a and  € ~ nm b The data λor ”i- curves , ”i- curves , and ”i- curve are shown. c insiμhts dose dependences oλ the peaks maμnitudes’ ratios … nm – curve I and … nm – curve II , λor λibers ”i- circles and ”i- squares . Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Optical Society oλ “merica .

Figure . Dose dependences oλ backμround loss measured at nm λor λibers ”i, ”iduced with permission λrom Kir’yanov [ ]. Copyriμht© , Optical Society oλ “merica .

, and ”i-

. Repro‐

Figure . “ttenuation spectra oλ ”i-doped alumino-silicate λiber ”i- , obtained beλore curve , dose  € and aλter curve , dose  € electron irradiation. “ part oλ the spectra is shown where the main resonant-absorption peaks oλ ”i “l centers are observed. Inset hiμhliμhts the behavior oλ one oλ the peaks at ~ nm aμainst the irradiation dose. Reproduced with permission λrom Kir’yanov [ ]. Copyriμht© , Optical Society oλ “merica .

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Radiation Effects in Materials

Oλ separate interest is the behavior oλ absorption peak  .€ Since absorption oλ ”“Cs in this spectral area is covered by an absorption peak oλ OH μroups nm , we λound reasonable to zoom the spectral transλormations λor this ranμe see Figure b . From the λiμure, it is seen that the contribution in attenuation which comes λrom contaminatinμ by OH μroups is unchanμed aλter irradiation, while the one stemminμ λrom the presence oλ the ”i-dopants is substantially reduced. One more example oλ the irradiation-induced bleachinμ eλλect is μiven in Figure where we make insiμht to the spectral transλormations in the absorption peaks within the – nm band  € aλter electron irradiation oλ the rest oλ ”i-doped μermano-silicate λibers, ”i- and ”i- . These two have, in pristine state, a hiμher and lower than ”i- concentration oλ ”“Cs, correspondinμly see Figure . The spectra shown in Figure have been obtained beλore dose  € black curves and and aλter dose  € blue curves and electron irradiation. Qualitatively, the same law, viz., bleachinμ oλ the resonant-absorption peaks throuμh the interval – nm as the result oλ electron irradiation, is revealed, now λor λiber samples ”iand ”i- . Hence, the bleachinμ eλλect is λound to be a μeneral essence oλ the ”i-doped μermanosilicate λibers. The next μraphs plotted in Figure a, b demonstrate how absorption peaks  € namely, its main subpeak centered at nm and  € the one centered at ~ nm are reduced via electron irradiation these dose dependences are shown λor all λibers ”i- , ”i- , and ”i- . The initial absorption values in peaks these are μiven near each curve in Figure a, b were taken λrom the attenuation spectra oλ pristine dose  € samples. Curves – λor resonantabsorption peaks  € Fiμure a and  € Fiμure b were obtained λrom the spectra shown in Fiμures and aλter subtractinμ the backμround loss, which μrows at irradiation reλer to Figure and also to Figure . Note that, λor λiber ”i- characterized by the lowest content oλ ”i centers, the data are provided λor peak  € only because the measurements λor peak  € were below the resolution limit. It is seen λrom Figure a, b that bleachinμ oλ the resonant-absorption bands aλter electron irradiation is a characteristic λeature oλ the ”i-doped μermano-silicate λibers. Furthermore, resonant absorption bleachinμ in peaks  € and  € has almost the same character, which is evident λrom Figure c where we plot the ratio oλ absorption coeλλicients in peaks  € and  € in λunction oλ irradiation dose λor ”i- and ”isamples see curve I. “s seen, this quantity is kept virtually unchanμed via irradiation, beinμ equal to its initial value measured in pristine state. The same conclusion can be made λor the ratio oλ absorption coeλλicients in peaks at ~ nm and ~ nm  € , see curve II in Figure c . This is a justiλication oλ that resonant-absorption bands peaked at ~ ,~ , and ~ nm and accordinμly emission-active ”“Cs attributed by these peaks, see Fiμures – are aλλected by the same or by a very similar manner by electron irradiation. Then, as seen λrom Figure , the backμround loss measured in the dip at nm, between the absorption peaks ascribed to ”“Cs in μermano-silicate λiber see Figure monotonously increases with dose, a common eλλect λor all kinds oλ Ge-doped silica materials. Growth oλ the backμround loss is even more pronounceable in the UV. The results oλ electron irradiation oλ the ”i-doped alumino-silicate λibers exempliλied λor λiber ”i- deserve a separate attention. Figure shows how the attenuation spectra oλ this λiber

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

are chanμed aλter a maximal dose oλ electron irradiation. It is seen λrom a direct comparison oλ curves and obtained beλore and aλter irradiation that in the ”i-doped aluminate λiber an opposite to the case oλ the ”i doped μermanate λiber trend exists, viz. instead oλ resonantabsorption bleachinμ see Figures – , weaker but detectable extra absorption arises in the peaks centered at ~ and ~ nm. Inset to Figure examples the dynamics oλ the absorption peak at ~ nm upon dose note that almost the same dose behavior is observed λor the peaks at ~ and ~ nm. We do not present here the results oλ measurinμ λluorescence spectra and λluorescence liλetimes adherent to ”“Cs, obtained beλore and aλter irradiation the reader is advised to reλer to [ ] λor details. The only thinμ to mention in this reμard is that the λluorescence spectra oλ both types oλ the ”i-doped λibers μermano- and alumino-silicate were not aλλected qualitatively by electron irradiation, with a sole result oλ the latter beinμ a decrease/increase oλ inteμrated λluorescence power emitted by the μermano-/alumino-silicate λibers. “lso note that almost no chanμe was detected in the λluorescence kinetics λor pristine and irradiated λibers oλ these two types . ± . / . ± . ms . Thus, the chanμes in the resonant-absorption peaks, detected above, should be related to a decrement/increment oλ the ”“Cs concentration in the μerma‐ nate/aluminate ”i-doped λibers. . . Discussion First oλ all, the attenuation spectra oλ typical pristine ”i-doped μermano- and alumino-silicate λibers Figure need examination. From these spectra that cover an extended wavelenμths interval – nm , one can recoμnize the λinμerprints€ oλ ”i dopants in the λibers, appearinμ throuμh the correspondent resonant-absorption bands these were reλerred to as ”i Ge,Si and ”i “l centers. Speciλically, the main absorption peaks at , , and nm the ”i-doped alumino-silicate λiber seem to belonμ to the center ”i “l , whereas the ones at , , and nm the ”i-doped μermano-silicate λiber «to physically similar ”i Ge and ”i Si ”“Cs. Note that the peaks at nm look indistinμuishable λor both λiber types so they can be related to Si λorminμ host oλ both the μlasses see e.μ. Reλs. [ , ] . Other spectral λeatures not linked to the presence in the λibers oλ Ge, “l, and Si oriμinate either λrom contaminatinμ by water OH peaks at and nm or λrom special desiμn oλ the λibers the cutoλλ peaks . Reμardinμ the experimental results on electron irradiation, they are remarkable but not enouμh to make a deλinite conclusion on real processes involved. The only thinμ to propose is possible correlation oλ the rise and decrease oλ IR emission-active ”“Cs concentrations aλter electron irradiation in alumino- and μermano-silicate λibers, respectively, with known λacts that substitutional λour-coordinated “l in alumino-silicate μlass is a hole trap, whereas substitutional Ge in μermanate μlass is an electron trap [ , , – ]. This diλλerence can stronμly aλλect the residuary charμe state oλ the ”i specie aλter the electron irradiation. The process oλ radiation-induced charμe trappinμ oλ both electrons and holes can be accompanied by the λormation oλ diλλerent point deλects say, Ge , Ge , GeE’, “l-E’, and “l-ODCs [ , ] , detectable in ESR and optical spectra’ measurements.

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. Concluding remarks Resuminμ, we have shown in this chapter that a diversity oλ eλλects can be encouraμed at irradiatinμ optical silica-based λibers with dopants oλ diλλerent kinds by hiμh-enerμy βelectrons. This has been demonstrated on the examples oλ Ce- and Ce “u -doped aluminophospho-silicate λibers, Yb-doped μermano-alumino-silicate λibers, and ”i-doped μermanoand alumino-silicate λibers. The data presented in this Chapter is a collection oλ our recent results, published in and in part reproduced λrom Reλs [ , , ]. In each case, unavoidable darkeninμ€ oλ the λibers in VIS arises as the main λeature oλ electron-irradiation. Meanwhile, such treatment allows one to detect interestinμ laws in transλormations that active€ dopants presented in the λibers suλλer as well as to propose mechanisms responsible λor the phenomena involved. “lso note that the new knowledμe arisinμ as the result oλ considerinμ these trans‐ λormations can be helpλul λor some applications oλ these or other doped λibers in such areas as dosimetry on nuclear plants and space technoloμy and can be as well valuable when desiμninμ λiber devices lasers and ampliλiers λor the next-day telecom systems.

Acknowledgements The author sincerely acknowledμes the λollowinμ people, contributinμ in the researches hiμhliμhted above Dr. N.S. Kozlova National University oλ Science and Technoloμy MISIS , Moscow, Russia «λor assistance in electron irradiation oλ all λibers Drs. M.C. Paul and S. Ghosh Central Glass & Ceramic Research Institute, Kolkata, India «λor providinμ samples oλ Ce and Ce “u -doped λibers and λor discussions Drs. V.V. Dvoyrin, V.M. Mashinsky, and E.M. Dianov Fiber Optics Research Center oλ the Russian “cademy oλ Sciences, Moscow, Russia «λor providinμ samples oλ ”i-doped λibers and valuable discussions Dr. Yu.O. ”armenkov Centro de Investiμaciones en Optica, Leon, Mexico «λor participatinμ in experi‐ ments with Ce and Ce “u -doped λibers and useλul discussions. The author also thanks support λrom the Ministry oλ Education and Science oλ the Russian Federation under the Increase Competitiveness Proμram oλ NUST «MISiS»€ Grant К .

Author details “lexander V. Kir’yanov “ddress all correspondence to [email protected] Centro de Investiμaciones en Optica Center λor Optical Researches , Leon, Guanajuato, Mexico

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

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] “rai T, Ichii K, Taniμawa S, Fujimaki M. Gamma-irradiation-induced photodarkeninμ in ytterbium-doped silica μlasses. Proc. SPIE. paper OK.

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] ”urshtein Z, Kalisky Y, Levy SZ, Le ”oulanμer P, Rotman S. Impurity local phonon nonradiative quenchinμ oλ Yb λluorescence in ytterbium-doped silicate μlasses. IEEE J. Quant. Electron. – .

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Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers http://dx.doi.org/10.5772/63939

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] Rulkov “”, Ferin ““, Popov SV, Taylor JR, Razdobreev I, ”iμot L, ”ouwmans G. Narrow-line, nm CW bismuth-doped λiber laser with . W output λor direct λrequency doublinμ. Opt. Expr. – .

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] ”uλetov I“, Dianov EM. ”i-doped λiber lasers. Laser Phys. Lett.

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] Fujimoto Y, Nakatsuka M. Inλrared luminescence λrom bismuth-doped silica μlass. Jpn. J. “ppl. Phys. L –L .

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] Menμ XG, Qiu JR, Penμ MY, Chen DP, Zhao QZ, Jianμ XW, Zhu CS. Near inλrared broadband emission oλ bismuth-doped aluminophosphate μlass. Opt. Expr. – .

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] Dvoyrin VV, Kir’yanov “V, Mashinsky VM, Medvedkov OI, Umnikov ““, Guryanov “N, Dianov EM. “bsorption, μain, and laser action in bismuth-doped aluminosilicate optical λibers. IEEE J. Quant. Electron. – .

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] Penμ M, Zhao Q, Qiu J, Wondraczek L. Generation oλ emission centers λor broadband NIR luminescence in bismuthate μlass by λemtosecond laser irradiation. J. “m. Ceram. Soc. – .

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] Ou Y, ”accaro S, Zhanμ Y, Yanμ Y, Chen G. Eλλect oλ μamma-ray irradiation on the optical properties oλ PbO-” O -SiO and ”i O -” O -SiO μlasses. J. “m. Ceram. Soc. – .

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] “lessi “, “μnello S, Gelardi FM, Grandi S, Maμistris “, ”oscaino R. Twoλold coordinated Ge deλects induced by μamma-ray irradiation in Ge-doped SiO . Opt. Expr. – .

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] ”uλetov I“, Semenov SL, Vel’miskin VV, Firstov SV, ”uλetova G“, Dianov EM. Optical properties oλ active bismuth centres in silica λibres containinμ no other dopants. Quantum Electron. – .

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] Skuja LN, Trukhin “N, Plaudis “E. Luminescence in μermanium-doped μlassy SiO . Phys. Status Solidi “. K –K .

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Chapter 2

Radiation Effects in Optical Materials and Photonic Devices Dan Sporea and Adelina Sporea Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62547

Abstract The chapter continues previous reviews on radiation eλλects in optical λibers and on the use oλ optical λibers/optical λiber sensors in radiation monitorinμ, published by InTech in and , by reλerrinμ to radiation eλλects in optical materials, with an empha‐ sis on those operatinμ λrom visible to mid-IR, and on some photonic devices such as optical λibers λor ampliλiers, λiber ”raμμ μratinμs and lonμ period μratinμs. The λocus is on optical materials and λiber-based devices desiμned λor both terrestrial and space‐ borne applications. For the presented subjects, an overview oλ available data on Xrays or μamma rays, electron beams, alpha particles, neutrons, and protons eλλects is provided. In addition, comments on dose rate, dose, and/or temperature eλλects on materials and devices deμradation under irradiation are mentioned, where appropri‐ ate. The optical materials and photonic devices reliability under ionizinμ radiation exposure is discussed as well, as the opportunities to use them in developinμ radia‐ tion sensors or dosimeters. The chapter includes an extensive biblioμraphy and reλerences to last published results in the λield. Novel proposed applications oλ photonic devices in charμed particle beam diaμnostics, quasi-distributed radiation λield mappinμ and the evaluation oλ radiation eλλects in materials λor mid-IR spectroscopy are brieλly introduced to the reader. Keywords: radiation eλλects, optical materials, optical λibers, λiber ”raμμ μratinμ, lonμ period μratinμ

. Introduction The μoal oλ this chapter is to continue previous reviews on radiation eλλects in optical λibers [ ] and on the use oλ optical λibers and optical λiber sensors in radiation related measurements [ ],

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Radiation Effects in Materials

by reλerrinμ to radiation eλλects in optical materials and some photonic devices. “ccordinμ to this vision, the chapter is orμanized to cover the interaction oλ ionizinμ radiation with some optical materials and optical λibers, λollowed by a reλerence to radiation eλλects on some photonic devices based on optical λibers. The discussion addresses radiation eλλects produced by both enerμetic photons and charμed particles, as appropriate [ ]. In this context, an overview oλ some recently published results in the λield is included, with a λocus on oriμinal authors’ contributions. The terrestrial radiation environments where optical and photonics components can be λound include, but are not limited to, hiμh enerμy physics experiments, nuclear power plants [ ], λusion installations as the International Thermonuclear Experimental Reactor – ITER, or the Laser Méμajoule – LMJ [ – ], hiμh power laser installations [ ], nuclear waste repositories [ ], hiμh enerμy physics [ , ], medical equipments λor diaμnostics or treatment [ ]. On the other side, applications oλ optical components or photonic devices can be λound in spaceborne instrumentation [ – ]. These environments involve various types oλ ionizinμ radiations, dependinμ on the application considered X-rays or μamma rays, electron beams, alpha particles, neutrons, protons, and ”remsstrahlunμ [ , , ].

. Radiation effects in optical materials . . Optical materials Extensive research was involved in the elucidation oλ deλects λormation in μlasses, as investi‐ μations were perλormed in μlasses with various compositions under ionizinμ and non-ionizinμ radiation exposure. The studies were λocused either on the materials deμradation upon irradiation or on the possible use oλ such materials in radiation dosimetry [ , ]. The radiation induced chanμes depend on the μlass composition, total dose, dose rate, temperature and humidity durinμ exposure, and post irradiation heatinμ oλ the sample [ ]. The operation oλ a μlass-based dosimeter can be decided as λunction oλ radiation sensitivity, linearity oλ the response, stability oλ the radiation produced eλλect, and possibility to re-use the material. ”esides μlass-based optical materials, radiation hardeninμ tests were perλormed on various other optical materials. More than years aμo radiation induced deλects were studied in ”aF crystals by exposinμ them to μamma rays λrom Gy to kGy and observinμ the optical attenuation recovery between and nm under UV radiation and the scintillatinμ siμnal [ ]. Samples λrom diλλerent manuλacturers exhibited radiation induced attenuation RI“ saturation startinμ λrom Gy. Crystal impurities and deλects are the primary source oλ the optical attenuation increase in the – nm and – nm spectral bands induced by μamma rays [ ]. ”aF and LaF were subjected to Ne and U ions at enerμies λrom . to . MeV/u bombardment, and their deμradation was investiμated by scanninμ λorce microscopy SFM , optical spectroscopy and surλace proλilometry. RI“ λor ”aF shown an increase at λ = , , and nm, while LiF crystals remained almost unchanμed spectrally. Surλace topoμraphy studies indicated the presence oλ hillock in the irradiated zone [ ]. Neutron irradiation was done on Y “l O , CaF and LiF and RI“ was monitored λor UV-visible spectra. For Y “l O samples an increase oλ the optical attenuation was present λor wavelenμth

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

lower than – nm. CaF and LiF sinμle crystals deμrade their optical transmission aλter neutron exposure mostly in the – nm reμion. When heated aλter the irradiation RI“ λor the three crystals recovers accordinμ to diλλerent patterns [ ]. Gamma irradiation dose rate Gy/h, total doses oλ Gy, kGy, kGy, kGy was conducted on CaF , Fused Silica and Clearceram in order to evaluate their qualiλication λor space applications. RI“ modiλication was measured over the – nm spectral interval at normal incidence. The optical investiμations were completed by ellipsometry tests beλore and aλter the irradiation, λrom nm to μm. In the case oλ Clearceram, λor example, three absorption bands located at . , . , and . eV are present. Over a quite lonμ period these peaks decrease exponentially [ ]. The scintillation properties oλ diλλerent optical materials were studied λor their possible use in the development oλ radiation detectors. Two radiation induced luminescence RIL bands were observed in polycrystalline ”aF irradiated by X-rays at K, λor the wavelenμths intervals – nm and around nm [ ]. Under X-ray irradiation, ZnSe crystals present a deμra‐ dation oλ the optical transmission at – nm, and λour luminescence spectra at λ = nm, nm, nm and nm [ ]. “n X-ray induced RIL peak was reported in CaF crystals at λ= nm, accompanied by a small one at about nm [ ]. Sapphire is one oλ the most intensively studied optical material under diλλerent ionizinμ radiation X-ray kV, m“ and β λrom a Sr source at . Gy/min [ ] MeV proton λlux × p cm- s- and MeV arμon . × ion cm− s− and MeV krypton . × ion − − cm s [ ] μamma rays dose rate . Gy/s, total dose Gy combined with neutrons enerμy . MeV and λluences oλ – n cm− [ ] λast neutrons enerμy . MeV and − λluence oλ . × n cm [ ], neutron irradiation λollowed by heatinμ enerμy MeV, λlux oλ . × n cm- s- and λluence up to n cm− , maximum temperature °C [ ]. Sapphire proved to be radiation hardened under μamma exposure up to hiμh doses Gy , but is more susceptible to optical transmission deμradation under μamma-neutron irradiation as the optical attenuation increases with the λluence λor wavelenμths below nm. RIL spectra chanμe under μamma irradiation in relation to RI“ modiλication [ ]. For λast neutron irradiation, absorption bands develop at λ = , , , and nm, while post irradi‐ ation excitation produce photoluminescence siμnals at λ = , and nm [ ]. Hiμh purity “l O crystals present absorption peaks at λ = , , , , and nm, when irradiated by λast neutrons. Post irradiation annealinμ up to °C heatinμ contributes to partial recover oλ RI“. Excitation at λ = nm induces luminescence at λ = , , nm [ ]. The RIL associated to the F- and F+- bands was λound to be dependent on the proton dose [ ]. The invention oλ quantum cascade laser QCL [ ] and subsequent research in the λield made possible the development oλ compact, very accurate, and portable spectroscopic instruments λor the mid-IR spectral ranμe oλ interest λor orμanic compounds identiλication – μm . Tunable QCLs or arrays oλ QCLs operatinμ at diλλerent wavelenμths proved to be aλλordable substitutes λor Fourier transλorm IR FTIR systems to be used in astronomy, astrophysics, astrochemistry, and space missions [ , ]. In order to operate reliably under extreme conditions as components to be included in spaceborne equipment, the composinμ parts oλ

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Radiation Effects in Materials

such equipment have to be tested under speciλic radiation exposure. Within this context, a proμram to evaluate λor the Romanian Space “μency passive and active mid-IR components is under way. In this chapter, reλerence will be made to tests carried out on mid-IR windows materials CaF , ”aF , ZnSe, and sapphire«“l O . The subjects oλ these investiμations are COTS components-on-the-shelλ products, manuλactured in Europe and China. The windows have – mm diameter and a thickness oλ – mm. Considerinμ the complex space radiation environments which can be encountered durinμ extra planetary missions, irradiation tests were run under various irradiation conditions μamma rays dose rate oλ . kGy/h +/– . %, λour irradiation steps at total doses oλ . kGy kGy kGy kGy , alpha particles doses λrom . × kGy to . × kGy, dependinμ on the window material, at three beam currents oλ , and μC, beam diameter – mm , protons at p cm− , p cm− , p cm − λluences , electron beam dose rate oλ kGy/min, total dose – several kGy . Gamma and electron beam irradiation were perλormed in air at room temperature, while proton and alpha particle irradiation were done in vacuum [ – ]. Prior and aλter each irradiation step the samples were measured in relation to their optical transmittance and reλlectance over the spectral ranμe λrom nm to μm. Figure illustrates the setup λor spectral reλlectance evaluation, which was carried out with the Gooch and Houseμo OL Series “utomated Spectroradiometric Measurement System and the accessories tunμsten lamp and IR μlower, diλλractinμ μratinμs, inteμratinμ spheres, reλlectance standards, optical detectors - Si & Ge, PbS, InSb and HμCdTe appropriate to each spectral interval over which the measurements were done. Optical transmittance oλ the irradiated samples was used to assess the color centers μeneration RI“ in mid-IR optical materials under various irradiation conditions type oλ radiation, dose, and dose rate . In the mean time, durinμ alpha particle irradiation the RIL was monitored on-line in order to associate this siμnal with the presence oλ some dopants/ impurities. The peak wavelenμths oλ the detected radioluminescence are λ = nm Caλ , λ= nm ”aF , λ = nm ZnSe , and λ = nm “l O . Siμniλicant decrease oλ the optical transmission was obtained λor CaF and ”aF , below μm, while a drop oλ the optical trans‐ mission over the investiμated spectral ranμe . – μm was noticed λor all the materials except λor sapphire, case when the transmission chanμe was smaller as compared to other midIR materials. For the same purpose, R”S Rutherλord backscatterinμ spectrometry measure‐ ments were done on the investiμated samples.

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

Figure . The sketch a and the picture b oλ the setup λor spectral reλlectance measurements over the UV to mid-IR Reproduced with permission and courtesy oλ Gooch and Houseμo .

Spectral reλlectance measurements were associated to optical microscopy tests as charμed particles impinμinμ on windows surλace aλλect its quality Figure

.

Figure . The deμradation oλ windows surλace quality aλter alpha particle irradiation a ”aF Laura Mihai .

b ZnSe Courtesy oλ

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Radiation Effects in Materials

For the λirst time, THz Terahertz spectroscopy and imaμinμ were introduced Figure the analysis oλ irradiated mid-IR optical materials.

in

Figure . D plot oλ the THz reλlected siμnal λor ”aF window as the sample was scanned in the XY plane, λor – THz a the λrequency siμnal alonμ the X axis b , at a resolution oλ μm Courtesy oλ Laura Mihai .

. . Optical fibers Optical λibers were suμμested to be possible candidates λor radiation dosimetry throuμh RI“, RIL or thermoluminescence monitorinμ [ ]. Such applications were considered in the case oλ μlass optical λibers and plastic optical λibers as well. The radiation induced eλλects depends stronμly on the optical λiber composition oλ the irradiated optical λibers, a detailed discussion on radiation induced deλects in Pure Silica Core PSC and doped optical λibers can be λound in [ , ]. Optical λibers based on diλλerent dopants were proposed λor radiation dosimetry usinμ the optical attenuation chanμe under μamma irradiation TiO and GeO + TiO in the silica core SM optical λibers [ ] Ge/“l co-doped SM λibers [ ] P O doped step-index MM [ ]. Dependinμ on the experiment, low doses dose rates oλ . – Gy/h, λor total doses up to Gy [ ], moderate dose rates – Gy/h, total doses oλ – Gy [ ] or hiμh doses dose rates oλ , or Gy/min, and the maximum total dose oλ kGy [ ] were used. RI“ was measured

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

either at λ = , and nm [ , ] or at λ = , and nm [ ]. The recovery oλ the irradiation induced attenuation was studied at room temperature, throuμh photobleachinμ “r laser radiation at λ = nm or by heatinμ the samples °C in O atmosphere at the pressure oλ psi . Some oλ the studied samples dependinμ oλ the dopants concentration, wavelenμth considered, dose used, and radiation sensitivity indicate a linear dependence oλ RI“ with the dose, its independence with the dose rate and low recovery, which provide the μround λor applications in radiation dosimetry. Step index multimode, . mole% P O co-doped with and without . mole% GeO in the core optical λibers were tested under μamma irradiation and shown a linear response at nm λor dose rates oλ . to Gy/h, and a radiation sensitivity oλ . – . d” m− Gy, up to a maximum dose Gy [ ]. “s the samples present an independence oλ the radiation response on the dose rate and a low recovery they seem to be suitable λor medical dosimetry. “n investiμation oλ μamma rays on polarization maintaininμ PM optical λibers to be used in interλerometric λiber optic μyroscope IFOG λor spaceborne assembles was carried out on three types oλ λibers i pure-silica-core, ii P-doped mol% , and μermanium Ge-doped mol % , as they were exposed to total doses oλ Gy and kGy. RI“ was monitored over the spectral ranμe – nm, with a λocus on and nm. “ll the three λibers are more sensitive to radiation at nm than at nm, and the most deμradation as it concerns RI“ was observed in the case oλ the P-doped optical λiber [ ]. On-line evaluation oλ μamma radiation produced RI“ was investiμated in cm lonμ Co/Fe co-doped alumino-silicate optical λibers λabricated by modiλied chemical vapor deposition MCVD , and exposed to dose rates oλ . , . , . , and . Gy/min, λor min to total doses oλ , , , and Gy [ ]. The measurements were done at nm with a Yokoμawa “Q C optical spectrum analyzer. Followinμ the irradiation, the attenuation in the doped λiber increases times as compared to a reλerence optical λiber SMF- TM , and a small decay oλ the RI“ siμnal was noticed aλter the irradiation ended. “n almost linear relationship was present between RI“ and the dose up to a total dose oλ . kGy at . Gy/min, which recom‐ mend this optical λiber λor radiation dosimetry, as RI“ dose rate independence was observed. The perλormances oλ Ce-doped alumino-phospho-silicate optical λibers without “u . wt.% “l O , . wt.% P O , . wt.% CeO and with “u co-dopinμ . wt.% “l O , . wt.% P O , . wt.% CeO , and . wt.% “u O , produced by MCVD, were evaluated under electron beam irradiation at enerμy oλ ~ MeV up to the total doses oλ e/cm , × e/cm , e/ cm , × e/cm , e/cm , and . × e/cm . RI“ was monitored between nm and nm, and post irradiation photobleachinμ under He-Ne laser radiation laser λ = nm and UV. The results oλ the study indicated that the Ce/“u-doped optical λibers are more suitable λor λiber-based dosimetry [ ]. In the last years, the research λocused also on the X-ray irradiation keV enerμy eλλects on various optical λibers PSC, Ge-doped, P-doped, Fluorine-doped/ co-doped, in some cases the irradiation beinμ combined with sample heatinμ to °C [ , ]. The irradiation outcomes in chanμinμ the optical λiber characteristics were investiμated by online RI“ measurements, conλocal micro-luminescence CML and electron paramaμnetic

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resonance EPR , λor total doses up to MGy dose rate oλ Gy/s . RI“ modiλications in the UV-visible spectral ranμe λor Ge/F co-doped optical λibers produced under diλλerent conditions draw speed and tension were monitored with a mini optical λiber spectrometer Ocean Optics HR and deuterium-haloμen DH liμht source. “lmost complete recovery oλ the irradiation induced attenuation was observed at room temperature λor λ = nm, corre‐ spondinμ to Ge deλects, at room temperature durinμ the day λollowinμ the exposure [ ]. For various production conditions and diλλerent chemical composition the RI“ vs. total irradiation dose μraph indicates a linear dependency up to the dose oλ kGy. “n interestinμ aspect in the research oλ optical λiber behaviour exposed to radiation is represented by the evaluation oλ radiation induced chanμes as heatinμ is applied to the investiμated sample. Diλλerent types oλ multimode UV optical λibers deep UV enhanced, hiμh OH step-index solarization resistant, hiμh OH step-index UV enhanced extended spectral response, H -loaded, step-index were tested under μamma irradiation. In some circumstan‐ ces, the samples were heated to K while irradiated, as the variation oλ the optical attenu‐ ation at speciλic wavelenμths in the UV spectral ranμe λ = nm, λ = nm, λ = nm and λ= nm was monitored. For some wavelenμths λ = nm and λ = nm H -loadinμ improves radiation resistance, while heatinμ durinμ the irradiation oλ the same optical λiber increases their radiation sensitivity [ ]. “ complex research was carried out to evaluate the combined eλλect oλ radiation keV X-ray, Gy/s dose rate and total dose λrom . KGy to MGy and heatinμ up to °C, λor diλλerent types oλ optical λibers [ ]. The results oλ this investiμation indicated that no unitary behavior with temperature durinμ radiation exposure can be predicted in the case oλ PSC, Ge-doped, P-doped, Fluorine-doped optical λibers, as in some situations λiber compositinμ, temperature ranμe, total dose the sample heatinμ has no eλλect in compensatinμ the deλects μeneration, while in some others RI“ increases or decreases with the temperature increase. In any case, some oλ the study conclusions reλer i to the possible use oλ such λibers in radiation dosimetry, especially at low doses, and ii to the limited lenμth oλ λiber which can be incorporated into distributed radiation sensinμ systems. “ recent contribution to the use oλ optical λibers in radiation dosimetry reλers to some studies carried out in cooperation with a team workinμ at the European Synchrotron Radiation Facility, in Grenoble on UV multimode optical λibers subjected to synchrotron radiation [ ]. In this experiment were tested λive types oλ commercially available UV optical λibers and oλλline measurements concerninμ the deμradation oλ the optical λibers transmission in the UVvisible spectral ranμe were done, as color centers developed upon exposure to synchrotron radiation. The measurements were perλormed λor diλλerent doses , , , , , , and Gy. The radiation induced optical attenuation was monitored in relation to recovery phenomenon both at room temperature and aλter samples heatinμ to K. The chanμe oλ optical transmission and the increase oλ the attenuation at speciλic wavelenμths λ = nm λ= nm λ = nm λ = nm λ = nm were perλormed usinμ the setup presented in Figure . The measurements were done with a dedicated soλtware control developed under LabVIEW, by usinμ a broadband UV-visible liμht source, a sensitive optical λiber spectrometer, and an optical λiber multiplexer.

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

Figure . The sketch oλ the measurinμ setup liμht source optical λiber attenuator spectrum oλ the liμht source optical λiber multiplexer optical λiber sample absorption spectrum optical λiber mini spectrometer laptop connectinμ optical λibers irradiated optical λiber samples. I, multiplexer input O, multiplexer output.

The μraphical user’s interλace is illustrated in Figure . The multiplexer is employed to connect diλλerent tested samples to the liμht source and the spectrometer and help λor the determination oλ the optical absorption λrom

nm to

nm. The operator can preset the number oλ

averaμinμ cycles, the box car value and can select the wavelenμths oλ interest to be monitored. Oλ interest λor these tests was to monitor speciλic wavelenμth associated to the presence oλ color centers in μlass λibers. ”y observinμ the dependency oλ the optical absorption on the total irradiation dose at the speciλied wavelenμths Figure

can be estimated the linearity oλ this

dependency and the spectral interval over which a saturation eλλect occurs. This can help to evaluate the possible use oλ these optical λibers in radiation dosimetry, at speciλied dose rates.

Figure . The LabVIEW μraphical user’s interλace λor the experimental setup Courtesy oλ Laura Mihai .

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Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

Figure . The dynamics oλ the color center λormation as λunction oλ the dose i.e. Gy and Gy in this case λor the λive tested optical λibers, at λ = nm, λ = nm, λ = nm, λ = nm a SFS / T Fiberμuide Industries Inc. b UVS / Fiberμuide Industries Inc. c HPSUV P Oxλord Electronics d FVP /UVM Polymicro Technoloμies e FVP /UVMI Polymicro Technoloμies .

“s a premiere, the use oλ THz spectroscopy and imaμinμ to assess the synchrotron radiation induced chanμes in the core and coatinμ oλ the investiμated optical λibers Figure was reported. This approach makes possible the visualization€ oλ the dielectric constants chanμe oλ the irradiated materials.

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Figure . The THz spectral siμnal oλ the core a and coatinμ b oλ an irradiated UV optical λiber, λor two synchrotron radiation doses Gy and Gy Courtesy oλ Laura Mihai .

The potential to employ P-doped core multimode optical λibers as X-ray keV radiation detectors λor doses up to kGy, under diλλerent dose rates , , Gy/s was studied by monitorinμ in real time the RI“ in the spectral ranμe λrom to nm. The results indicated a sub linear dependence oλ the irradiation induced attenuation with the dose and dose rate. The temperature did not chanμe RI“ durinμ the irradiation λor values between and °C. The hiμhest radiation sensitivity was observed at nm, ~ . d”/m− Gy− [ ]. For the case RI“ values durinμ the irradiation is dependent on the radiation dose and exhibit a recovery aλter the exposure is interrupted, a diλλerential scheme can be applied when the measurand is represented by the diλλerence oλ RI“ at two wavelenμths, λ = nm and λ = nm, respectively [ ]. “nother novelty recently introduced reλers to the test oλ μamma radiation on perλluorinated polymer optical λibers pPOF . These results complement the investiμations previously reported in literature on the spectral characteristics oλ μamma irradiated PMM“ optical λibers. In this case, commercially available MM perλluorinated λiber GiμaPOF- SR λrom Chromis Fiberoptics were exposed to μamma ray at a dose rate oλ . kGy/h λor total doses oλ , , , and kGy. The irradiation took place at maximum temperature oλ °C, and the samples were measured beλore and aλter the irradiation usinμ a -OTDR λrom Luciol Instruments, operatinμ at and nm [ ]. In addition, strain tests were also perλormed to evaluate the mechanical deμradation oλ the polymer λiber under μamma irradiation. For doses up to kGy the attenuation vs. the dose presents a linear dependency with a radiation sensitivity oλ . ± . d” m- kGy− at nm, and . ± . d” m- kGy− at nm. The obtained results suμμest the possible use oλ these optical λibers in radiation dosimetry. The dynamics oλ the color centers λormation under μamma irradiation was investiμated by on-line measure‐ ments and by monitorinμ RI“ chanμe at several wavelenμths λ = , , and nm . The hiμhest radiation sensitivity was noticed at λ = nm up to . kGy dose, while the best linearity response oλ RI“ vs. dose was obtained at λ = nm λor a dose reachinμ . kGy [ ]. The last decade recorded as a breakthrouμh the use oλ sapphire optical λibers in radiation environments, as sapphire supports very hiμh operatinμ temperatures and presents minor

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

optical transmission chanμes when exposed to ionizinμ radiation over a wide spectral ranμe [ ]. Recently, sapphire optical λibers were subjected to neutron λlux oλ . × n cm− s− and a μamma dose rate oλ kGy/hr dose in sapphire λor a total neutron λluence oλ . × n cm − and total μamma dose oλ . MGy [ ]. The optical attenuation in the sapphire λiber was measured on-line over the – nm spectral ranμe. The major RI“ occurs below the nm measurinμ limit. “ chanμe oλ RI“ was noticed as the sample was heated to °C, under μamma irradiation [ ]. The use oλ optical λibers λor distributed measurements in ionizinμ radiation environments became a hot topic in the last years as several tests were run and some possible applications were suμμested Raman and ”rillouin strain/ temperature sensinμ [ , ] Rayleiμh temper‐ ature sensinμ [ ]. Tests were perλormed on standard communication, hiμhly doped GeO , Fdoped optical λibers [ , ] and PSC , Ge-doped, radiation hardened and “l-doped optical λibers [ ], at dose rates oλ Gy/h [ ], . kGy/h [ ], kGy/h [ ], and total doses oλ kGy [ ], kGy [ ], MGy [ ]. RI“ proved to be the major challenμe in usinμ optical λibers distributed ”rillouin temperature sensors, as the operatinμ distance is reduced to several hundreds oλ meters due to irradiation [ ]. Limitations in temperature monitorinμ are present also in the case oλ Rayleiμh-based setup [ ]. Temperature measurements usinμ Raman scatterinμ encounters some diλλiculties as the temperature evaluation uncertainty is quite hiμh upon irradiation [ ]. The complementary aspect oλ interest is represented by the possible use oλ radiation sensitive optical λibers λor distributed dosimetry. Two approaches were proposed to be used i the optical time domain reλlectometry – OTDR [ ], ii the optical λrequency domain reλlectome‐ tery – OFDR [ ]. In both experiments the λiber samples were subjected to μamma irradiation P-doped optical λibers [ ] and standard communication, “l-doped, and P-doped optical λibers [ ], at dose rates Gy/h at °C and Gy/h at °C, total dose oλ about kGy [ ], and dose rate oλ mGy/s, λor a total dose oλ Gy [ ]. The OTDR approach exhibits a limited spatial resolution λor distributed dosimetry. Dependinμ on the optical λiber type, the inter‐ roμatinμ instrument dynamic ranμe and the dose, the usable lenμth oλ the dosimetric λiber is limited to several centimeters [ ]. . . Rare earth-doped optical fibers Generally, radiation hardeninμ tests oλ rare earth-doped optical λibers were perλormed in relation to their possible use in space applications such as inter-satellite communications and λiber optic μyroscopes FOGs applications [ – ]. The investiμations λocused on the radiation induced absorption in the optical λiber and on chanμes oλ the emission eλλiciency. Tests were carried out under μamma ray [ , , ], neutrons [ ], protons [ – ], or X-ray [ ] exposure. The reported studies indicate that • the irradiation results are primarily dependent on the dose and not on the type oλ irradiation involved [ ], • the device deμradation is λunction more on the co-dopant concentration than on the rareearth elements [ ],

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• annealinμ and photobleachinμ can contribute to partial recovery oλ the irradiation induced eλλects [ , , ]. Tests on photobleachinμ oλ two Erbium-doped λibers EDFs subjected to . and . kGy μamma irradiation were carried out at two laser wavelenμths and nm . “ hiμher eλλiciency was achieved with the shorter wavelenμth excitation. The annealinμ eλλect induced by the nm laser is comparable to that present in the case oλ thermal annealinμ at K [ ]. In another experiment, an EDF was tested under electron irradiation beam enerμy . MeV, total dose kGy , and the output power, noise λiμure and the central wavelenμth were measured aλter the irradiation, with the pump at nm and detection at nm. The central wavelenμth did not chanμe aλter irradiation, while the output power and noise λiμure were deteriorated i.e. the output power dropped λrom to – d”m λor the same pump level . Within weeks, the two parameters partially recovered [ ]. Sinμle mode and multi-mode Yb-doped optical λibers, actinμ as ampliλiers at nm, were subjected to μamma rays and mixed μamma-neutron irradiation, up to a total dose oλ Gy Si [ ]. It was noticed a linear decrease oλ the output power with the irradiation dose. “ sliμht recovery was observed at room temperature, aλter hours. In his PhD thesis, Fox [ ] concluded that EDFs are more radiation sensitive than Yb +-doped λibers, and the most radiation hardened to μamma ray are optical λibers oλ Er +/Yb + co-doped type. In this investiμation, the radiation induced deμradation increases with the increase oλ the dose rate. Optical λiber preλorms oλ Yb-λree aluminosilicate core, Yb-doped “l-λree silicate core, Ybdoped alumino-silicate cores and Yb-λree μermanosilicate core produced by MCVD and solution-dopinμ techniques were irradiated by kV X-rays, at ~ . Gy SiO / min, λor doses up to . – . kGy [ ]. The eλλects oλ the irradiation were studied by thermally stimulated luminescence TSL and optical absorption measurements. Investiμations were carried out to evaluate the inλluence oλ H -loadinμ oλ EDFs, under pumpinμ at and nm, as the samples were subjected to μamma irradiation, havinμ doses λrom . to kGy. One such sample was a H -loaded EDF, while the other was H -λree carbon-coated [ ]. “t nm pumpinμ a photobleachinμ eλλect was observed which increases the eλλiciency oλ the process especially in the H -loaded optical λiber. No such eλλect was present with the pump radiation oλ nm. H -loadinμ and the use oλ a hermetical coatinμ oλ the optical λiber, which prevents H diλλusion, produce a radiation resistant EDF [ ]. One approach to enhance the radiation resistance oλ the optical ampliλier consists in the use oλ Er-doped-nanoparticles optical λibers [ ]. “nother proposed method is based on the dopinμ oλ the optical λiber core with Ce, reducinμ in this way the radiation sensitivity [ ]. Tests on a thulium doped optical λiber ampliλier were perλormed under neutron irradiation and a . d” was observed λor a dose oλ Gy, which is close to the computed values [ ]. The development oλ ”i co-doped silica optical λibers [ ] havinμ an extensive emission operation ranμe λrom to nm called researchers attention on their investiμation

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

under ionizinμ radiation. Tests run under μamma irradiation, dose rate – . kGy/h and maximum total dose – kGy, on ”ismuth/Erbium/Ytterbium co-Doped Fiber – ”EYDF [”i] ~ . , [Er] < . , [“l] ~ . , [Ge] ~ . , [Yb] ~ . atom%, respectively, indicated the λormation oλ bismuth related active center ”“C , as the absorption at nm is increased siμniλicantly, while the absorption at lonμer wavelenμth diminishes [ ]. In the case oλ ”i/“l-co-doped silica optical λibers the λluorescence peak increases with the increase oλ the μamma dose dose rate, Gy/h maximum total dose, kGy , when the sample is pumped at nm. The preλorm oλ the investiμated materials had the λollowinμ concentra‐ tions Si« mol/% core , Ge« mol/% core , O« mol/% core and inner layer , ”i« . mol/% core and inner layer , and “l« . mol/% core and inner layer . It is presumed that this enhancement oλ the photoluminescence siμnal upon irradiation is due to creation oλ subvalence ”i ions [ ]. “nother investiμation was λocused on the eλλect oλ μamma irradiation dose rate – . kGY/h, total doses oλ , , , and kGy on samples oλ ”ismuth/Erbium co-doped λiber ”EDF . The irradiation has siμniλicantly increased unsaturable absorption by about d”. This corresponds to a very siμniλicant unsaturable attenuation coeλλicient chanμe oλ ~ d”/cm. The results indicate that the saturable absorption oλ the ”EDF at nm is also increased by about d”. This corresponds to a siμniλicant saturable attenuation coeλλicient chanμe oλ d”/cm. The increase in saturable pump absorption implies that the irradiation has siμniλicantly increased the number oλ bismuth related active centers ”“C-Si . In this case the overall emission at nm which is related to ”“C-Si is only sliμhtly decreased while the unsa‐ turable absorption is siμniλicantly increased. “ μood radiation survivability oλ the ”EDF λor emission or ampliλication was noticed [ ].

. Radiation effects in photonic devices . . Fiber Bragg gratings Fiber ”raμμ μratinμs were excessively studied under various type oλ ionizinμ radiation μamma ray [ , , ], neutron [ ], mixed μamma-neutron [ – ] or . MeV protons [ ]. In most cases, the chanμes oλ the F”G ”raμμ wavelenμth are relatively low. Tests were carried out usinμ Type I, Type II, Type I“, Type II“, chemical composition or λs laser enμraved μratinμs, and were λocused on the eλλect oλ λiber composition, dose rate, total dose, heatinμ durinμ the irradiation or possible photobleachinμ durinμ the exposure to ionizinμ radiation [ ]. For example, Type I μratinμs produced in H -loaded standard communication optical λibers SMF TM or ”/Ge co-doped optical λibers present an increase oλ the central wavelenμth λollowed by a plateau, with an overall chanμe between pm to pm, under . MGy exposure. In the case oλ Type II μratinμs written in ”/Ge co-doped optical λibers exhibit a decrease oλ the central wavelenμth between - and - pm. Deμradation – % oλ μratinμs reλlectivity was produced aλter irradiation, while no recovery was observed in the studied sensors [ ]. “ quite siμniλicant impact oλ μamma radiation on Ge-doped core optical λibers was observed as such uncoated λibers are immersed in water durinμ μamma exposure [ ], λor

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a total dose oλ up to MGy. Generally, all the investiμations carried out on radiation eλλects on F”Gs λocused on the possible use oλ such devices in radiation environments λor temperature or humidity [ ] monitorinμ. Under some desiμn circumstances optical λiber type, technoloμy used to write the μratinμ , these modiλications are siμniλicant, makinμ possible the use oλ F”Gs as radiation detectors [ , ]. More recently, the use oλ F”Gs developed in sapphire optical λiber was proposed λor moni‐ torinμ very hiμh temperature in nuclear reactors [ ]. Throuμh these studies, the paradiμm was chanμed as [

]

• F”Gs were produced in radiation hardened optical λibers by two-beam interλerometer and deep ultraviolet λs laser radiation • λor the λirst time F”Gs written in both standard commercial optical λibers and radiation hardener optical λibers were tested, exposed to the electron beam λrom a linear accelerator • a mash oλ F”Gs was used λor beam diaμnostics oλ charμed particle beams, as a novelty. This research indicated a linear dependence oλ the ”raμμ wavelenμth shiλt with the irradiation dose λor commercially available F”Gs and μratinμ produced in radiation hardened optical λibers, and this shiλt was monitored by measurinμ simultaneously with a thermocouple the temperature chanμe in the irradiation plane. This aspect is important because no saturation or permanent modiλication oλ F”G wavelenμth was observed hence these sensors can be used λor on-line measurements. The principle oλ the charμed particle beam diaμnostics is illustrated in Figure , λor the case oλ an electron beam havinμ a diameter oλ about mm. The spatial resolution is limited by the number oλ F”Gs enμraved in an optical λiber, their individual lenμth and the distance between two adjacent F”Gs. In the described prooλ-oλ-concept desiμn, μratinμs havinμ mm and mm lenμth were employed. “s compared to other solutions λor charμe particle beam monitorinμ arrays oλ Faraday cups ionization chambers micro strip metal detector pepper-pot device, slit-μrid or rotatinμ slits scintillatinμ screen or μas detector λlat panel detectors, arrays oλ p-i-n diodes movinμ wire or vibratinμ wire scanners there are several advantaμe oλ this approach its immunity to electro-maμnetic noise, remote monitorinμ capability and the possibility to multiplex the acquired siμnals by usinμ λew connectinμ lines. The operation oλ the proposed instrument is similar to that employed λor laser beam diaμnos‐ tics. In the evaluation oλ a laser beam quality an imaμe sensor is used to acquire the transversal distribution oλ the laser beam’s intensity. Periodically, the electric charμe μenerated inside the imaμe sensors is removed upon readinμ and new acquisition starts. In this implementation the instrument operation is based on the proved reliability oλ the tested F”Gs under electron beam exposure and on the linear shiλt oλ F”Gs ”raμμ wavelenμth with the temperature in the detection plan, and hence with the deposed enerμy by the charμe particle beam. Prior to the use, the F”Gs were calibrated as it concerns their wavelenμth chanμe vs. temperature. When the charμe particle beam is propaμatinμ λrom the linear accelerator output its diameter increases in the detection plan due to its diverμence Figure a . In the detectinμ plan item in Figure b a mesh composed oλ F”Gs is placed, the sensors beinμ embedded into a thermally insulatinμ material to prevent the lateral dissipation oλ the heat. “s the

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

individual μratinμs are exposed to diλλerent beam enerμies their temperature increases accordinμ to the enerμy deposed on each detectinμ site. In this way, in time, a map oλ the transλerred enerμy at each location is obtained.

Figure . The operation principle oλ the electron beam analyzer a the movinμ shutter used to interrupt F”Gs expo‐ sure to the electron beam the incident electron beam beam diameter at the exit oλ the linear accelerator λocusinμ system movinμ shutter the electron beam diameter at its incidence on the detection plan detectinμ plan. b The position oλ the F”Gs mash the detectinμ plan electron beam pattern on the detection plan F”Gs connectinμ optical λibers optical λiber interroμator bars symbolizinμ the inteμral enerμy deposited on a particu‐ lar F”G at a speciλied moment. c Example oλ the data acquired λor the kGy dose [ ]. d Top view oλ the shutter and coolinμ system.

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The detector operates as an enerμy inteμrator dose related measurements . Permanently, the central wavelenμth oλ all sensors is acquired by a Micron Optics optical λiber interroμator, which makes possible the real time mappinμ oλ the electron beam cross section enerμy distribution. In order to avoid saturation, periodically the F”Gs siμnal has to be reset€ by blockinμ the electron beam and λorced coolinμ the F”Gs array. For this purpose a thick mm “l shutter restricts under the soλtware control Figure a and d the exposure oλ the F”Gs by interruptinμ the electron beam. Durinμ the interval the beam is blocked, a cooler pushes air over the sensors’ matrix. The “l shutter μoes back and λorth as the array has to be exposed or cooled. The λlow chart λor the instrument operation is presented in Figure .

Figure . The λlow chart oλ the electron beam analyzer.

Durinμ the Initialization€ step, the shutter is closed, the F”Gs are cooled, and the λunctioninμ parameters set by the operator are introduced in the system. Iλ a STOP command was issued by the operator the system stops and displays in D λormat the inteμrated enerμy to which each sensor was subjected, measured as ”raμμ wavelenμth shiλt in response to the local temperature increase. Iλ no STOP command was μiven the system periodically acquires on the central wavelenμth shiλt λor each sensor and checks iλ the maximum set temperature was reached by any oλ the F”Gs. Iλ this temperature was reached the system stops and displays the results as a D representation. Iλ no such siμnal was received the soλtware commands durinμ the Data acquisition€ step the closinμ oλ the shutter and the coolinμ oλ the F”Gs array. The periodicity oλ the coolinμ cycles, and the upper limit oλ the temperature to which any oλ the sensors can be subjected are set by the operator. The ”raμμ wavelenμth shiλt with the dose increase is μiven in Figure . In this case, durinμ the irradiation pause, the μratinμ’s coolinμ

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

was obtained by convection in air and not by λorced coolinμ. The proposed instrument can be used durinμ the adjustinμ process oλ the charμed particle accelerator or to check the stability in time oλ the output beam.

Figure . The chanμe oλ the ”raμμ wavelenμth with the dose increase. Periodically, between two exposures the μra‐ tinμ was cooled by natural convection [ ].

“ novelty in the λield can be considered the investiμation oλ F”Gs perλormances written in polymer λibers under λast neutrons irradiation. In the paper it is suμμested that neutrons produce a deμradation oλ the λiber structure, which in turn causes a shiλt oλ the ”raμμ wave‐ lenμth up to pm. The wavelenμth chanμe with neutron dose can be exploited in radiation dosimetry [ ]. . . Long period gratings Lonμ period μratinμs LPGs were tested only under μamma ray exposure [ ]. Most oλ the measurements were perλormed oλλ-line [ – ], with some exceptions when the device behavior was monitored durinμ the irradiation [ , ]. The LPGs were obtained by diλλerent techniques CO laser or UV enμravinμ [ ], electric arc-discharμe E“D technique [ ], CO laser point-by-point writinμ [ ], as chiral μratinμs [ ], havinμ a turnaround point T“P desiμn produced by a CO laser [ ]. Various optical λibers were employed N-doped and Gedoped optical λibers [ ], pure-silica-core/ F-doped silica claddinμ λibers [ ], SMF- TM [ ], core doped with P, Ge, F, rare earth elements [ ], photosensitive λibers ”/Ge co-doped [ ]. The irradiation conditions are modiλied λrom kGy [ ] up to . MGy [ ]. Dependinμ on the optical λiber type, the writinμ technique, the dose rate/total dose used, the reported results led to diλλerent conclusions i no eλλect was observed on the LPG transmission spectrum λor doses lower than kGy [ ], lower than kGy [ ] or as hiμh as . MGy [ ], ii a nm shiλt oλ the transmission deep was noticed λor doses oλ kGy [ ], iii very hiμh shiλt oλ the dual resonance deep nm is present λor a dose oλ kGy [ ]. This variety oλ investiμations

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outcomes suμμest that, by an appropriate selection oλ the above mentioned parameters, LPGs can be produced either to be radiation hardened or with pronounced radiation sensitivity, appropriate to be used in radiation dosimetry. No chanμe in the temperature sensitivity oλ LPGs upon irradiation was observed [ ]. “ new proposed approach in studyinμ μamma irradiation eλλects on LGPs Includes several novelties [ , ] • the use oλ an OFDR model LUN“ O”R , operatinμ in the transmission mode or, λor comparative purpose, oλ an optical λiber interroμator model sm • LPGs on-line monitorinμ when the irradiation is on and oλλ, which makes possible the observation oλ room temperature recovery • the comparative evaluation oλ the radiation induced LPG chanμes λor μratinμ produced in standard communication and specially desiμned radiation hardened optical λibers. The use oλ the OFDR improved drastically the detection S/N as compared to classical readinμ with an optical spectrum analyzer. Durinμ the irradiation the sensors were encapsulated into ceramic radiation transparent cases to avoid any strain induced chanμes in the LPG spectrum, and in the mean time, the μratinμs were placed into a thermally insulated box. The temperature was permanently monitored both inside this box and in the irradiation chamber and temper‐ ature related corrections were applied to the LPG characteristics. ”ased on the reλerred papers, Figure illustrates comparatively the behaviour oλ μamma irradiation on the LPG developed into a standard communication optical λiber LPGsc and one written in a radiation hardened optical λiber LPGrh . The wavelenμth deep oλ the two samples move in opposite directions, the wavelenμth oλ the μratinμ produced in the standard communication λiber increases with the dose increase, while λor the other one the wavelenμth decreases with the dose increase. ”esides that, it can be noticed the maμnitude oλ the two chanμes, LPGsc beinμ by λar more

Figure . The chanμe oλ the wavelenμth deep λor two LPGs written in standard communication optical λibers LPGsc and in F-doped core optical λiber LPGrh.

Radiation Effects in Optical Materials and Photonic Devices http://dx.doi.org/10.5772/62547

sensitive. The λluctuations oλ the wavelenμth deep values durinμ μamma exposure as well as the partial saturation trend are associated to the on-oλλ operation oλ the irradiation λacility. In this way, λor the λirst time the recovery eλλect durinμ the irradiation pauses was observed. ”ecause λor the LPGrh the wavelenμth chanμe is by λar less siμniλicant than that in the case oλ LPGsc, it can be expected that the λirst one can be used in radiation environments as a sensor λor temperature/humidity, while the second LPG can be employed within speciλic dose ranμe as an optical λiber-based dosimeter.

. Conclusions The last λour to λive years brouμht additional data concerninμ radiation eλλects in optical λibers and optical λiber-based devices as new materials, technoloμies and possible applications in radiation environments emerμed. In the λrame oλ this chapter, the major trends were presented and some novel techniques and applications promoted recently were addressed, in relation to diλλerent types oλ irradiations i.e. electron beam, synchrotron radiation . In this way, the data reviewed in previous publications are updated and the extensive possibilities oλλered by new materials and experimental setups in usinμ radiation eλλects on optical λibers were demon‐ strated. ”y λocusinμ such type oλ research on newly developed λibers plastic, micro-structured, multi-core and by usinμ novel photonic devices based on optical λibers, new classes oλ equipment will emerμe λor terrestrial applications dosimetry, medicine, remote and distrib‐ uted monitorinμ and λor space missions.

Acknowledgements The authors acknowledμe the λinancial support oλ the Romanian Executive “μency λor Hiμher Education, Research, Development and Innovation Fundinμ UEFISCDI , under μrant / , project Sensor Systems λor Secure Operation oλ Critical Installations - SOCI€ and oλ the Romanian Space “μency ROS“ throuμh the project Evaluation oλ Components λor Space “pplications - ECS“€, μrant / .

Author details Dan Sporea* and “delina Sporea *“ddress all correspondence to dan.sporea@inλlpr.ro Photonics Investiμations Laboratory, National Institute λor Laser, Plasma and Radiation Physics, Maμurele, Romania

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] Reμo G, Fernandez “F, Gusarov G, ”richard ”, ”erμhmans F, Santos JL. Eλλect oλ ionizinμ radiation on the properties oλ arc-induced lonμ-period λiber μratinμs. “pp. Opt. . DOI . /“O. .

[

] Sporea D, Stancălie “, Neμut D, Pilorμet G, Delepine-Lesoille S, Lablonde L. On-line tests oλ an optical λiber lonμ-period μratinμ subjected to μamma irradiation. IEEE Photonics J. - . DOI . /JPHOT. .

[

] Sporea D, Stăncalie “, Neμuţ D, Pilorμet G, Delepine-Lesoilled S, Lablonde L. Com‐ parative study oλ lonμ period and λiber ”raμμ μratinμs under μamma irradiation. Sensor “ctuator “-Phys. . DOI http //dx.doi.orμ/ . /j.sna. . .

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Chapter 3

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors Dejan Nikolić and Aleksandra Vasić-Milovanović Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62756

Abstract The aim oλ this paper is to explore the impact oλ increased μamma and neutron radia‐ tion on the PIN photodiodes and phototransistors and their output characteristics. Special attention was paid to the successive impact oλ μamma and neutron radiation when the components were located in the λield oλ μamma radiation and aλter that in the λield oλ neutron radiation. The impact oλ successive irradiation was compared with the inλluence oλ μamma and neutron radiation when they appear individually. “n important result oλ this research is the observation that neutron irradiation oλ photovoltaic detectors, applied aλter μamma irradiation, leadinμ to partial reparations oλ distorted semiconductor structure and increasinμ disrupted output characteristics photocurrent, spectral response . Monte Carlo simulation oλ μamma photons transλer throuμh the crystal lattice oλ the semiconductor has been shown that the cause oλ such eλλect oλ neutron radiation is a larμe number oλ divacancies caused by successive operation oλ the previous μamma radiation and the neutron radiation itselλ. Divacancies have created the basis λor increased μeneration oλ charμe carriers by direct transλer tunnelinμ oλ carriers throuμh the traps recombination centers . This is so called intercenter charμe transλer. Keywords: photovoltaic detectors, μamma and neutron radiation, divacancies, inter‐ center charμe transλer, Monte Carlo simulation

. Introduction Science and technoloμy that deals with photovoltaic semiconductor detectors is an area with an extremely rapid development in the last years. The reasons λor this are, on the one hand,

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Radiation Effects in Materials

practically countless possibilities oλ application oλ these detectors optical communication systems, medical devices, military equipment, automatic control systems, various electronic devices , and, on the other hand, miniaturization oλ electronic components and development oλ these devices mass production allowed them to have relatively low cost and to be accessi‐ ble to the wide population. Particularly interestinμ applications oλ semiconductor photovolta‐ ic detectors are in military systems, medical devices and equipment, and cosmic systems. These are areas where the probability λor photovoltaic detectors to be in increased radiation λield is very larμe. The area oλ photovoltaic detectors and radiation type which they can be exposed is very larμe. This work is limited to the observation oλ the PIN photodiodes and phototransistors and their behavior in terms oλ μamma and neutron radiation considerinμ that with particle emission λrom the core, as a rule, there have been a simultaneous de-excitations descendant core by a discrete μamma-ray emission. Semiconductor devices, thereλore, are exposed to summary eλλect oλ neutron and μamma radiation. The aim oλ this paper is to explore the impact oλ increased μamma and neutron radiation on the PIN photodiodes and phototransistors and their output characteristics. Special attention was paid to the observation oλ semiconductor devices' behavior when they have been exposed to the λield oλ μamma radiation and aλter that to the λield oλ neutron radiation successive μamma and neutron radiation .

. Experimental Experimental measurement in this paper was carried out on the commercially available photovoltaic detectors. In this experiment, the λollowinμ were used .

λour types oλ silicon PIN photodiodes ”P Vishay, and SFH F“ by Osram ,

, ”PW

.

two types oλ silicon NPN phototransistors ”PW tronic and LTR by LITEON .

N, ”PW

all manuλactured by

manuλactured by Teleλunken elec‐

Devices were λirst exposed to μamma radiation λrom Co source and then, aλter days, to “m-”e neutron and μamma source. ”oth sources were housed in Institute oλ Nuclear Sciences Vinča€ in ”elμrade, Serbia. The dose oλ Co μamma source is Gy, the enerμy oλ . MeV, and halλ-liλe time oλ . years. The samples were placed in controlled environment at a distance oλ mm away λrom the radioactive source with a μlass between them. The dose rate was Gy/hr which was measured by electrometer with ionization chamber TW produced by PTW, Germany. Measurement uncertainty oλ the system is less than . %. “m-”e source emits μamma photons oλ low enerμy and keV with the activity oλ . × ”q, the intensity oλ the neutron emission oλ . × neutrons s− and the mean enerμy oλ the neutrons Enav = . MeV. The panels were at a distance oλ cm λrom the source,

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

so the photon equivalent dose rate is Ḣγ = mSv/hr, and the photon absorbed dose rate is Ḋγ = mGy/hr. Calculated neutron absorbed dose rate is Ḋn = . mGy/hr and the equivalent dose rate oλ neutrons is Ḣn = mSv/hr with the quality λactor Qn = . In this experiment, the semiconductor devices were placed at a distance oλ cm λrom the “m”e source, and the exposure period was . hr. Since the total absorbed dose, λor that distance, is Ḋtot = . mGy/hr and the total equivalent dose is Ḣtot = mSv/hr, the total absorbed dose λor material components is Dtot = . mGy and the total equivalent dose is Htot = mSv. ”oth irradiation and those λrom Co μamma source and those λrom perλormed in the air at a temperature oλ °C and relative humidity oλ

“m-”e source were – %.

”eλore and aλter every step oλ irradiation spectral response and photocurrent have been measured. The measurement were perλormed on the photodiodes and phototransistors, in hiμhly controlled conditions at room temperature, which have previously been removed λrom the irradiation room. Samples have been divided in two μroups. First μroup was irradiated only with neutron radiation and the second one with successive μamma and neutron radiation. For the λirst μroup, there have been perλormed three measurements oλ the photodiodes and phototransistors parameters .

λirst measurement just beλore neutron irradiation,

.

second measurement just aλter neutron irradiation,

.

third measurement

days aλter neutron irradiation.

For the second μroup there have been perλormed λive measurements oλ the photodiodes and phototransistors parameters .

λirst measurement just beλore μamma irradiation,

.

second measurement just aλter μamma irradiation,

.

third measurement

.

λourth measurement just aλter neutron irradiation,

.

λiλth measurement

days aλter μamma irradiation just beλore neutron irradiation ,

days aλter neutron irradiation.

In order to perλorm the lonμ-term isothermal annealinμ i.e. to μive detectors enouμh time to recovery, the third and λiλth measurement have been undertaken days aλter the irradiation. ”ecause oλ that, the chanμes occurrinμ in the samples oλ the second μroup aλter the λirst irradiation μamma can be considered as a permanent. Standard measurement equipment the proλessional diμital multimeter “MPRO”E XR was used λor measurement. Combined measurement uncertainty λor all measurements was less than . % [ , ]. In order to understand the state oλ the semiconductor crystal lattice aλter exposure to μamma radiation and beλore neutron irradiation, a Monte Carlo transλer simulation oλ μamma photons throuμh the photodiode and phototransistor have been perλormed.

71

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Radiation Effects in Materials

. Results and discussion . . Photodiodes and phototransistors response to neutron radiation Free neutrons, in small amounts, are everywhere in nature. The main source oλ neutrons is cosmic radiation. They also occur in nuclear reactions oλ natural α radiation and spontaneous λission oλ heavy nuclei. Neutron is a unique particle, it is uncharμed, has a relatively larμe mass, and leads to radioactive disinteμrations. From the point oλ nuclear reaction, neutrons are much more important than any other particles. “s neutral particles, neutrons do not have the ability λor direct ionization oλ materials. The basic mechanism oλ neutron interaction with the matter is via elastic collisions with atomic nuclei oλ environment. The interaction with electrons, althouμh it exist, is neμliμible. Thereby, neutron loses some oλ its enerμy and slows down, while the environment can suλλer diλλerent types oλ transλormation. Neutrons interact with the material in two diλλerent ways • throuμh collisions with other particles, • throuμh the process oλ absorption. In the case oλ hiμh-enerμy neutrons λast one , the dominant process is elastic scatterinμ, while with low-enerμy neutrons, the absorption process is more likely [ ]. Displacement oλ atoms can be compared with a collision between two solid spheres. Iλ the transλerred enerμy hiμher than the enerμy required λor displacement displacement energy Ed atom will be shiλted λrom their oriμinal positions in the lattice, and there will be deλect PKA —primary knock-on atom . “ssuminμ that there is enouμh enerμy, displaced atom could be able to move other atoms or to produce electron-hole pairs. In the case oλ very hiμh enerμy particles, a cascade distortion can be λormed. Diλλerent types oλ displacement deλects could occur due to neutron irradiation Figure • vacancies, • divacancies, • interstitials, • Schottky deλects, • Frenkel deλects. Fiμures – show the results oλ measurements oλ PIN photodiodes and phototransistors spectral response beλore and aλter neutron irradiation and aλter a period oλ days recovery are presented [ ]. “s can be seen λrom Fiμures to , neutron radiation caused the deterioration oλ photodiodes and phototransistors characteristics. Hiμh-enerμy particles like neutrons create much more displacement damaμes than μamma radiation. When an atom is ejected λrom its position, it creates a vacancy in the lattice. The ejected atom may recombine with a vacancy or stay in an interstitial position in the lattice.The

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

Figure . Displacement deλects [ ].

Figure . Spectral response oλ photodiodes beλore and aλter neutron irradiation.

vacancies are mobile and combine with other vacancies or with impurities oλ the semiconduc‐ tor [ , ], thus creatinμ recombination centers that cause the reduction oλ charμe carrier liλetime. “xness et al. [ ] showed that the damaμe to the crystal lattice and reduction oλ the charμe carriers liλetime are spatially dependent. Sporea et al. [ ] have calculated that the major deμradation oλ the photodiode responsivity, λor the total μamma dose oλ . MGy and to the neutron λluence oλ . × n/cm , occurs in the case oλ neutron irradiation . % as compared to the μamma irradiation . % . Steady deλects act as recombination centers and traps λor charμe carriers and because oλ that the resistance oλ the material could be increased [ ]. Mobile vacancies represent a stronμ recombination instrument λor capturinμ oλ minority charμe carriers and thus reduce their liλetime. Deλects responsible λor the capture oλ electrons called E-deλects while the H-deλects actually traps holes [ ]. Displacement deλects mainly aλλect the electrical characteristics oλ the semiconductor substrate and thus the electrical characteristics oλ the whole electronic compo‐

73

74

Radiation Effects in Materials

nents. “s a result, there have been the reduction oλ the spectral response and lower photocur‐ rent photodiode Figure .

Figure . Spectral response oλ phototransistor ”PW

beλore and aλter neutron irradiation.

Phototransistors are very susceptible to neutron radiation. Neutron radiation aλλects the characteristics oλ phototransistors primarily by creatinμ deλects in the crystal lattice which can dramatically increase the level oλ charμe carriers recombination. On the other hand, the increment oλ the recombination rate reduces the current μain. Many studies oλ the damaμe relocation mechanism in bipolar transistors have shown that the current μain oλ the transistor with a common emitter decreases with increasinμ oλ recombination centers number. The measurement data oλ phototransistors beλore and aλter irradiation showed that the adverse eλλects oλ neutron radiation are the most pronounced on transistors base current. Phototran‐ sistor is liμht controlled device where the output current is controled by the base current and briμhtness. Cluster deλects caused by λast neutrons are the dominant mechanism λor damaμinμ oλ phototransistors exposed to neutron radiation. Number oλ displaced atoms caused by neutrons is very larμe. The result is λorminμ oλ recombination-μeneration centers. Electronhole recombination causes a decrease oλ current μain. Generation oλ electron-hole pairs cause an increase in leakaμe current. Removinμ the majority charμe carriers and the reduction oλ carrier mobility causinμ an increase in voltaμe between the collector and emitter. Current μain is determined by the number oλ majority carriers emitted λrom the emitter which are passinμ throuμh the base as minority carriers and are collected by collectors as the major carriers. Increasinμ oλ density oλ recombination-μeneration centers due to deλects created by radiation causes a reduction oλ minority carrier liλetime, and because oλ that, the rate oλ electron-hole recombination in the base increases. “ccordinμly, the current μain decreases as a result oλ reduced injection oλ charμe carriers λrom the emitter to the collector and, as a result, the photocurrent and spectral response decreases Fiμures and [ ].

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

Figure . Spectral response oλ phototransistor LTR

beλore and aλter neutron irradiation.

In this experiment, a lonμ-term isothermal annealinμ at room temperature was applied. The recovery period, labelled as a short-term annealinμ, beμins immediately aλter the occurrence oλ damaμe and λully complete within a λew minutes to hour aλter irradiation. Damaμe, remaininμ aλter, that are oλten reλerred as a permanent damaμe. However, relatively slow process oλ recovery or lonμ-term annealinμ, continues even aλter the short-term annealinμ is completed [ ]. Recovery causes partially increasinμ oλ spectral response and the photocur‐ rent. Fiμures – show that the response oλ new, unused photodiode and phototransistor to neutron irradiation is in accordance with the theoretical principles described in the literature.

. . Photodiodes and phototransistors response to successive gamma and neutron irradiation In recent λew years there have been carried out a number oλ studies with the aim oλ observinμ the behavior oλ diλλerent photovoltaic detectors in terms oλ μamma and neutron radiation [ – ]. Most common topics were photodiode, as one oλ the most used and simplest types oλ optical sensors. The eλλect oλ μamma and neutron radiation on semiconductors is well known and described in the available literature. This chapter will present the results oλ research oλ behavior oλ photovoltaic detector due to successive μamma and neutron radiation. The samples were λirst exposed to μamma radiation and aλter days to neutron radiation. Figure shows the results oλ the photodiodes and the phototransistors spectral response measurements beλore and aλter μamma and neutron radiation [ ].

75

76

Radiation Effects in Materials

Figure . Spectral response oλ the reverse biased photodiode ”P

beλore and aλter μamma and neutron irradiation.

Figure . Spectral response oλ the reverse biased photodiode ”PW tion.

Figure . Spectral response oλ the reverse biased photodiode”PW

N beλore and aλter μamma and neutron irradia‐

beλore and aλter μamma and neutron irradiation.

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

Figure . Spectral response oλ the reverse biased photodiode SFH tion.

F“ beλore and aλter μamma and neutron irradia‐

“s it can be seen λrom Fiμures to , neutron irradiation, applied days aλter μamma irra‐ diation, at λirst was deteriorate response and characteristics oλ photodetectors. However, aλter days oλ recovery, there was a partial improvement oλ the spectral photodetector response and the increasinμ oλ photocurrent. The deμree oλ improvement is diλλerent λor each type oλ photodetector.

Figure . Spectral response oλ phototransistor ”PW

beλore and aλter μamma and neutron irradiation.

77

78

Radiation Effects in Materials

Figure

. Spectral response oλ phototransistor LTR

beλore and aλter μamma and neutron irradiation.

Neutron irradiation, by itselλ, causes the λormation oλ displacement damaμe in photodiodes and phototransistors, which leads to the deμradation oλ their electrical characteristics, as is shown in Chapter . Fiμures – . However, iλ it is applied aλter the μamma radiation, neutron radiation makes such chanμes which increasinμ the eλλiciency oλ the recovery process and, as a result, we have improved electrical characteristics. To achieve these eλλects to be occurred, the concentration oλ charμe carriers must be increased in semiconductor material. Takinμ previous studies into account [

,

–

], it can be concluded that the possible cause is

tunnelinμ oλ charμe carriers supported by traps and increased μeneration. Deλects in the material represent traps λor the λree charμe carriers and that can lead to tunnelinμ supported by traps, and this increases the tunnelinμ current at low voltaμes which are commonly attributed to SILC Stress-Induced Leakage Current [ –

]. Tunnelinμ supported by

traps is a process where particle spend some time trapped in the deλect trap beλore tunnelinμ throuμh the barrier Trap Asissted Tunneling—TAT [ ,

]. This process is caused by inelastic

transλer oλ charμe carriers with the help oλ emission oλ phonons [ Let the electron λrom the λield

in Figure

].

receive enouμh enerμy to cross the barrier and

came to the area . This process undermines the law oλ conservation oλ enerμy λor a short period oλ time determined by Heisenberμ’s uncertainty principle. Now, iλ some other electron λrom the λield tunneled in a similar way in a similar time in the area , then total number oλ electrons that are passed λrom area to area is one. This tunnelinμ is called inelastic tunnelinμ because the excited electron-hole pair occurs, which dissipates aλter a short time throuμh the interaction carrier-carrier [

].

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

Figure

. Elastic and inelastic tunnellinμ throuμh a double barrier [

].

Elastic tunnelinμ is the process oλ tunnelinμ oλ same electrons λrom and in the reμion with preservinμ oλ the phase which is why this process is coherent. Elastic tunnelinμ depends on the internal structure oλ the area between the barrier and the amount and polarization oλ the applied voltaμe. Inelastic tunnelinμ is the dominant process in comparison with the elastic tunnelinμ except in the case oλ low voltaμe, low temperature, or low density oλ quantum dot states [ , ]. “rea is also called a virtual state and simultaneous tunnelinμ throuμh this state, co-tunnelinμ. Shockley–Read–Hall model describes the process oλ recombination and the μeneration oλ charμe carriers in a semiconductor with the help oλ quantum tunnelinμ mechanism [ , , ]. The transition oλ an electron λrom the valence band to the conductive band represents the μeneration oλ electron-hole pair, because in the valence band, hole remains in the place oλ electrons which contribute to the current. The reverse process is recombination. In order to be transλerred λrom the valence band into the conductive band electron must have μreater enerμy than the enerμy μap. “s it may be deλects in the crystal structure oλ the semiconductor caused by impurities or other causes, eμ. radiation , it may appear within the bandμap. Such deλects are called traps and they represent enerμy levels that can trap electrons ejected λrom the valence band [ ]. “ccordinμ to Dharival-Rajvanshi's model, traps can be near the edμe oλ the valence and conduction band Tail State and near the Fermi level on both sides Dangling Bond . In order to move electron λrom the valence band into the trap, it requires much less enerμy than λor the transition to the conductive band, so the traps actually λacilitate the process oλ μener‐ ation oλ λree carriers. The probability that an electron will λall into the trap and spend some time in it depends on the material, the density oλ deλects in the enerμy μap, the present electric λield, temperature, concentration oλ electrons in the conduction band, and the concentration oλ holes in the valence band. Schokley–Read–Hall model assumes one level within a μap where electrons or holes can come, which dynamic is quasi-stationary [ , , ].

79

80

Radiation Effects in Materials

When μamma radiation and neutron radiation are actinμ individually on a photodiode there is, as the λinal result, an increase in the concentration oλ recombination centers which, accordinμ to Schokley-Read λormula [ ], result in a reduction oλ minority charμe carriers liλetime

t=

1 n0 + d n + n1 1 n0 + d n + p1 + á cn ñ × N t n0 + p0 + d n á c p ñ × N t n0 + p0 + d p

where τ = τp = τn is the liλe time oλ electrons and holes and Nt concentration oλ R-centers recombination centers which can accept both electrons and holes . The reduction oλ minority carrier liλetime causes photocurrent decreasinμ. Previously stated explanation is related to the inλluence oλ neutron irradiation on the new, previously non-irradiated photodiodes. However, iλ we chanμe the initial conditions, i.e. iλ the photodiode previously has been exposed to μamma radiation, the eλλects oλ neutron irradiation will be diλλerent. One oλ the results oλ μamma radiation are interstitial PK“ , vacancies, and their complexes [ , ]. Vacancies are also one oλ the main products oλ neutron irradiation oλ the material. When the material, which already contains a number oλ vacancies, is exposed to the eλλects oλ neutron radiation, there is hiμh probability that the deλects such as vacancies would be λound physically close to each other. When the two vacancies occur next to each other within the μrid, they λorm deλective complex called divacancies complex. This complex captures electrons and also can stress the homopolar bonds, which can lead to the termination oλ the connection. Straininμ oλ homopolar connections and its termination can lead to the release oλ one or two electrons λrom the deλective complex in the conductive band, which results in increased μeneration. In some previous studies, increased μeneration [ ] and increased recombination [ , ] have been observed throuμh the process oλ electron transλer directly between the deλects located close to each other without passinμ throuμh the conductive belt. This process can be very λast and thereλore dominant compared to the Shockley–Read–Hall process. In order to occur the intercenter charμe transλer, deλects must be physically close to one another. Two irradiation oλ the same material, such as μamma and neutron, allowinμ some deλects to be close to one another. The divacancy has three enerμy levels in the bandμap a hole trap and two aceptor states. In standard Shockley–Read–Hall theory, current μeneration in silicon depletion reμions is mediated by isolated deλect levels in the λorbidden bandμap. Generations occurs when a hole is emitted λrom the deλect level into the valence band i.e. electron captured λrom it and an electron is emitted into the conduction band. Each transition occurs with a rate, en or ep, and is μoverned by the time constant τne ili τpe. Iλ several deλect levels exist, they are reμarded as the sum oλ the individual components. In coupled deλect μeneration, illustrated in Figure , an electron is λirst captured by the donor state in the bottom halλ oλ the bandμap. This is an eλλicient process with time constant τpe beinμ very short hence the λractional occupation oλ this level is ≈ . The electron can then transλer directly to a hiμher state in a nearby deλect without μoinμ en = /τne and ep = /τpe.

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

via the conduction band. The time constant λor this step is denoted τ →2. The λinal transition to the conduction band then occurs as normal with a time constant τne2. The enhancement oλ the μeneration rate arises because the larμe transition λrom the valence band to the above midμap level is mediated by the donor level. This shortens the time taken λor the upper state to become λilled and hence increases its λractional occupancy [ , ].

Figure

. Schematic diaμram oλ Schokley–Read–Hall theory and intercenter charμe transλer μeneration processes [

].

The enhancement oλ the λractional occupancy increases the number oλ electrons μenerated per unit oλ time λrom a deλect state and hence increases the photocurrent [ ]. . . Monte Carlo simulation of radiation transfer through photovoltaic detectors In order to understand the state oλ the semiconductor aλter irradiation, Monte Carlo simula‐ tions oλ radiation particles transλer throuμh the material were perλormed. Monte Carlo simulation μets the answers by simulation oλ each individual particle and memorizinμ oλ certain aspects oλ their middle behavior. For simulation, FOTELP- K and MCNP proμrams were used. FOTELP- K is a proμram that μives the Monte Carlo simulation oλ the transport oλ photons, electrons, and positrons [ ], while the MCNP Monte Carlo N-Particle is a μeneral purpose soλtware that can simulate the transport oλ neutrons, photons, electrons, or a combi‐ nation oλ neutron/photon/electron throuμh arbitrary μeometric conλiμurations [ ]. For this experiment, two Monte Carlo simulation were made, γ-photon transλer throuμh the PIN photodiode and throuμh the phototransistor. The simulations were done with the aim oλ

81

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Radiation Effects in Materials

understandinμ the processes occurrinμ in the photodiode and phototransistor between μamma and neutron irradiation, i.e. to provide a review process, which is μamma radiation caused in a semiconductor since the λinal result oλ these processes represents the initial conditions λor neutron irradiation that λollowed. . . . Monte Carlo simulation of gamma photon transport through a pin photodiode Figure

Figure

presents a cross-section oλ a PIN photodiode used λor the simulation.

. Cross-section oλ a PIN photodiode [ ].

The results oλ Monte Carlo simulations are shown in Tables – and in Figure . Table shows the deposed enerμy per input particle in each zone oλ photodiode, where the zones are semiconductors area p+ zone , p zone , and n+ zone , and the pure semiconductor zone . Figure shows the ratio oλ enerμy absorbed durinμ each interaction in diλλerent layers per depth oλ semiconductors, i.e. each zone. Zone

Deposed energy eV

Relative error %

.

.

.

.

.

. .

.

Table . Deposed enerμy per input particle obtained by Monte Carlo simulation usinμ FOTELP- K .

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

Figure

. Depth dose distribution in PIN photodiode obtained usinμ FOTELP- K .

In order λor a lattice atom to be displaced, a minimum amount oλ enerμy must be transλerred to the tarμet atom. This threshold enerμy is called the displacement enerμy Ed threshold displacement energy—TDE [ , ]. ”y usinμ molecular dynamics MD simulations, Perlado et al. [ ] predicted TDE values, at K, ranμinμ λrom to eV λor Si. “veraμe TDE values oλ eV λor Si are suμμested by El-“zab and Ghoniem λrom MD simulations [ ]. In each zone oλ photodiode Table , and in almost every layer Figure deposed enerμy per incident particle is hiμh enouμh to move the atom, i.e. to create vacancy. Tables and show the probability oλ creatinμ new photons and electrons per incident particle photon throuμh individual interactions. Probability of creating new photons

Interaction that creates photons

.

E-

”remsstrahlunμ

.

E-

Positron-electron annihilation

.

E-

Electron x-rays

Table . Probability oλ creatinμ new photons per incident particle photon obtained usinμ MCNP.

Probability of creating new electrons

Interaction that creates electrons

.

E-

Pair production

.

E-

Compton eλλect

.

E-

Photoelectric eλλect

83

84

Radiation Effects in Materials

Probability of creating new electrons

Interaction that creates electrons

.

E-

“uμer photons

.

E-

“uμer electrons

.

E-

Electrons knocked out in a collision with impact electrons

Table . Probability oλ creatinμ new electrons per incident particle photon obtained usinμ MCNP.

”remsstrahlunμ is the interaction that has the hiμhest probability to μenerate new photons Table

, while the hiμhest probability λor creation have “uμer electrons Table

.

Tables and show the number oλ physical interactions in which are created or disappeared photons and electrons per input particle per cell . Physical interaction

Area —p+

Area —p

Area —i intrinsic

Area —n+

Area —Al contact

From neutrons ”remsstrahlunμ

.

E-

.

E-

.

E-

.

E-

.

E-

− .

E-

− .

E-

− .

E-

− .

E-

− .

E-

.

E-

.

E-

− .

E-

− .

E-

Electron x-rays

.

E-

.

E-

.

E-

.

E-

Total

.

E-

.

E-

.

E-

,

E-

Capture oλ photons P-annihilation Pair production Photonuclear eλλect

.

E-

Table . Number oλ physical interactions in which are created or disappeared photons per incident particle per cell obtained usinμ MCNP.

Physical interaction

Area —p+

Area —p

Area —i intrinsic

Pair production

.

E-

Compton recoil

.

E-

.

E-

.

Photoelectric eλλect

.

E-

.

E-

.

Electron “uμer

.

E-

.

PK“

.

E-

.

− ,

E-

.

E-

Photon “uμer

p-annihilation Total

.

Area —n+

Area —Al contact

.

E-

E-

.

E-

.

E-

.

E-

.

E-

.

E-

E-

.

E-

.

E-

E-

.

E-

.

E-

E-

.

E-

.

E-

.

E-

E-

.

E-

.

E-

− .

E-

.

E-

Table . Number oλ physical interactions in which are created or disappeared electrons per incident particle per cell obtained usinμ MCNP.

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

Simulation results show that the number oλ interactions that result in a vacancy i.e. PK“ primary knock-on atom are

to

times hiμher than all other possible types oλ interaction

Table «shaded part . “monμ the total number oλ electrons caused by μamma radiation in all areas oλ photodiode,

–

% is produced by PK“ in area

even up to

% . This is an

unequivocal siμn that the μamma radiation caused a very larμe number oλ vacancies. In order λor neutron irradiation oλ photodiodes applied aλter μamma radiation to cause intercenter charμe transλer and tunnelinμ supported by traps, as already mentioned, it is necessary λor neutron radiation to λorm deλects in a semiconductor vacancies , which are close to each other, and to create a suλλicient number oλ divacancies. “s a relatively heavy and uncharμed particles, neutrons, in a collision with the atoms oλ the crystal lattice, lead to the displacement oλ entire atoms λrom the lattice. This naturally causes the breakinμ and destruc‐ tion oλ the local lattice structure by displacinμ atoms and creatinμ vacancies. Displaced atom is called interstitial because it takes place in the space between knots, and a pair oλ interstitial atom and vacancy is called Frenkel deλect. Iλ the enerμy oλ incident neutron is hiμh enouμh, it can μive suλλicient enerμy to displaced atom, which can displace other atoms in the lattice. In the case oλ hiμh-enerμy incident neutrons, this process has a cascade avalanche character. This requires quick enerμy neutrons λrom

keV to

MeV. “t the end, all displaced atoms

lose their excess enerμy and the heat balance in the μrid established. Some oλ the atoms return to vacancies and reconstruct the structure oλ the local μrid. Some oλ these atoms come toμether with dopants or impurity atoms and λorm stable electrically inactive deλects, which do not contain recombination centers and trap. On the other hand, movinμ vacancies associate with impurity atoms, vacancies, and other donors λorminμ temperature stable deλects complex deλects that represent recombination centers and trap centers. Since the mean enerμy oλ neutrons λrom a source in the experiment was . MeV, it λollows that neutrons have suλλicient enerμy to cause a cascadinμ process oλ creatinμ vacancies. Previously, μamma irradiation created a larμe number oλ vacancies, increasinμ the probability λor vacancies, created by neutron irradiation, to be physically close to the preλormed vacancy. Divacancies, λormed like this, λacilitate intercenter charμe transλer supported by traps and provide increased μeneration oλ charμe carriers and this, as already mentioned in Section . ., leads to partial reparation oλ semiconductor structure and increase the spectral response and the photocurrent oλ the photodiode. . .2. Monte Carlo simulation of gamma photon transport through a phototransistor Figure

presents a cross-section oλ a phototransistor used λor the simulation.

The results oλ Monte Carlo simulations are μiven in Tables – . Tables

and

show the

probability oλ creatinμ new photons and electrons per incident particle photon throuμh individual interactions.

85

86

Radiation Effects in Materials

Figure

. Cross-section oλ a phototransistor [

].

Probability of creating new photons

Interaction that creates photons

.

E-

”remsstrahlunμ

.

E-

Positron-electron annihilation

.

E-

Electron x-rays

Table . Probability oλ creatinμ new photons per incident particle photon .

Probability of creating new electrons

Interaction that creates electrons

.

E-

Pair production

.

E-

Compton eλλect

.

E-

Photoelectric eλλect

.

E-

“uμer photons

.

E-

“uμer electrons

.

E-

Electrons knocked out in a collision with impact electrons

Table . Probability oλ creatinμ new electrons per incident particle photon .

“ccordinμ to the simulation results in any semiconductor λield within the phototransistor, there was no interaction in which are created or disappeared photons. Table show the

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

number oλ physical interactions in which are created or disappeared electrons per input particle per cell . Physical interaction

Area —emitter n

Area —base p

Area —colector n

Area —n + Area —Al contact

Pair production Compton recoil

.

E-

.

E-

.

E-

.

E-

.

E-

.

E-

.

E-

.

E-

.

E-

.

E-

Photoelectric eλλect Photon “uμer Electron “uμer PK“ p-annihilation Total

.

E-

Table . Number oλ physical interactions in which are created or disappeared electrons per incident particle per cell .

In phototransistor, as in the photodiode, the larμest number oλ inteμration caused by μamma radiation are vacancies PK“ Table «shaded part . When the semiconductor material, with structure like this, is exposed to neutron radiation, due to the nature oλ radiation, a number oλ new vacancies will be created toμether with those previously λormed. The λinal result oλ both types oλ radiation action are divacancies. “s already mentioned in Section . , divacancies cause the increased μeneration oλ charμe carriers throuμh the two dominant eλλects [ ] .

divacancies strain homopolar bond and break it, causinμ a release oλ one or two electrons

.

divacancies allow direct transλer oλ electrons between the deλects located close to each other without passinμ throuμh the conduction band intercentre charμe transλer [ ].

“ccordinμ to the results in Table the larμest number oλ divacancies have creatinμ in collector and the n+ area oλ phototransistor, increasinμ the concentration oλ electrons in these areas. On the other hand, due to Compton scatterinμ and “uμer electron and increases the concentration oλ electrons in the base. The λinal result oλ these eλλects is increasinμ the transistors photocurrent aλter neutron irradiation compared to its value aλter μamma irradiation , which is consistent with the results oλ the experiment presented in chapter . .

. Conclusion Gamma and neutron radiation, applied individually, aλλect the semiconductor material creatinμ deλects and chanμinμ the existinμ structure, which results in a chanμe in the output characteristics oλ the device and reducinμ their λunctionality. Gamma irradiation oλ silicon semiconductor causinμ numerous deλects oλ the crystal lattice. Monte Carlo simulations showed that in this experiment were represented almost all oλ the

87

88

Radiation Effects in Materials

eλλects described in the literature displacement oλ atoms PK“ , “uμer electrons, Compton scatterinμ, photoelectric eλλect, pair production. The impact oλ all these eλλects are maniλested in the μeneration oλ enerμy levels in the enerμy μap oλ crystal lattice which decreases the the minority charμe carriers liλetime resultinμ in a decrease in the photocurrent and spectral response. The biμ chanμe oλ phototransistors output characteristics can be explained by the inλluence oλ radiation on the current μain. The current μain is proportional to the minority charμe carriers liλetime so the deμradation oλ their liλetime directly aλλects the deμradation oλ current μain. This deμradation is caused by a displacement oλ atoms in the semiconductor bulk which aλλects the increase in the number oλ recombination centers and also oxidation oλ the oxide pasivisation layer especially over the emitter-base junction. Neutron irradiation causes damaμe in the photovoltaic detector which is primarily related to the displacement oλ silicon atoms λrom their positions in a μrid and creatinμ vacancies. Toμether with the vacancies, other eλλects appeared. Monte Carlo simulations showed that aλter the vacancies, the most λrequent are “uμer electrons, Compton scatterinμ, pair produc‐ tion, and the photoelectric eλλect. ”ecause oλ the combination oλ complex deλects, deλects that act as recombination centers are created and reduce the minority charμe carriers' liλetime which can lead to the deμradation oλ electrical parameters oλ photovoltaic detectors. When the semiconductor photovoltaic detectors are λirst exposed to μamma radiation and aλter a month to neutron, one can see that neutron radiation, applied aλter μamma radiation, partially corrects the characteristics oλ semiconductor devices which are exacerbated by μamma radiation, and that is maniλested throuμh increased spectral response and output photocurrent. This behavior oλ photodiodes and phototransistors can be explained by the increased μeneration oλ charμe carriers as a result oλ direct transλer tunnelinμ oλ the charμe throuμh the traps recombination centers . Direct intercenter charμe transλer is a process where charμe carriers spend some time trapped in the deλect oλ material traps beλore tunnelinμ throuμh the barrier. To become λree transλerred λrom the valence to the conductive band , an electron must have enouμh enerμy to overcome the enerμy μap. However, iλ the traps, that represent enerμy levels, are located near the edμe oλ the conduction and valence band and near the Fermi level on both sides accordinμ to Dharival-Rajvanshi model , then movinμ electrons λrom the valence band into the trap require notably less enerμy than λor direct transit to the conductive band, which means that the traps actually λacilitate the process oλ μeneration oλ λree carriers. “lso, accordinμ to the Shockley–Read–Hall model, there is one quasi-stationary enerμy level within the μap where the electron or hole could come. The probability that an electron will λall into the trap and spend some time in it depends, amonμ other causes, on the density oλ deλects in the enerμy μap. One oλ the ways to increase the density oλ deλects in the enerμy μap is creatinμ a larμe number oλ vacancies located physically close to each other in semiconductor material. Monte Carlo simulation oλ γ-photons transλer throuμh the photovoltaic detectors showed that μamma radiation leaves behind itselλ a number oλ displaced atoms vacancies . Since the radiation damaμe caused by neutrons primarily related to the displacement oλ atoms λrom their positions in the lattice oλ silicon semiconductor, i.e. λorminμ oλ vacancies, so neutron irradiation oλ photovoltaic detectors applied aλter μamma irradiation μives a possibility λor the creation oλ a suλλicient number oλ divacancies which can

The Impact of Successive Gamma and Neutron Irradiation on Characteristics of PIN Photodiodes and Phototransistors http://dx.doi.org/10.5772/62756

cause intercenter transλer and increased μeneration oλ charμes and thereby increasinμ the photocurrent and other parameters. The requirement λor creation oλ divacancies by neutron irradiation is the existence oλ vacancies in a semiconductor caused by previous μamma radiation.

Author details Dejan Nikolić * and “leksandra Vasić-Milovanović *“ddress all correspondence to nikolcorp@μmail.com ”rcko District Government, ”rcko, ”osnia and Herzeμovina Faculty oλ Mechanical Enμineerinμ, University oλ ”elμrade, ”elμrade, Serbia

References [ ] Stanković K., Vujisić M., Kovačević D., Osmokrović P. Statistical analysis oλ the characteristics oλ the some basic mass-produced passive electrical circuits used in measurements. Measurement. – . [ ] Vujisić, M., Stanković, K., Osmokrović, P. “ statistical analysis oλ measurement results obtained λrom nonlinear physical laws. “pplied Mathematical Modelinμ. – . [ ] G. ”arbottin and “. Vapaille. Instabilities in Silicon Devices, New Insulators, Devices and Radiation Eλλects. Elsevier . [ ] ”. Simić, D. Nikolić, K. Stanković, Lj. Timotijević, S. Stanković. Damaμe induced by neutron radiation on output characteristics oλ solar cells, photodiodes and phototran‐ sistors. International Journal oλ Photoenerμy. . ID . [ ] “. Holmes-Siedle and L. “dams. Handbook oλ Radiation Eλλects. Oxλord University Press . [ ] G.C. Messenμer and M.S. “sh. The Eλλects oλ Radiation on Electronic Systems, nd edition. Van Nostrand Reinhold Company New York . [ ] C.L. “xness, ”. Kerr, E.R. Keiter. “nalytic -D pn junction diode photocurrent solutions λollowinμ ionizinμ radiation and includinμ time-dependant chanμes in the carrier liλetime λrom a nonconcurrent neutron pulse. IEEE Transactions on Nuclear Science. – . [ ] D.G. Sporea, R.“. Sporea, C. Oproiu, I. Vat฀. Comparative study oλ μamma-ray, neutron and electron beam irradiated index-μuided laser diodes. in Proceedinμs oλ the

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th European Conλerence on Radiation and Its Eλλects on Components and Systems R“DECS ' . P“ –P“ . [ ] G.E. Schwarze, “.J. Frasca. Neutron and μamma irradiation eλλects on power semicon‐ ductor switches. In Proceedinμs oλ the th Intersociety Enerμy Conversion Enμineer‐ inμ Conλerence IECEC ' . – . [

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[

] M.”. El Mashade, M. “shry, Sh.M. Eladl, M.S. Raμeh. Experimental measurements oλ some optoelectronic devices beλore and aλter μamma irradiation. Journal oλ Micro‐ waves and Optoelectronic. – .

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] S.J. Watts, J. Matheson, I.H. Hopkins-”ond, “. Holmes-Siedle, “. Mohammadzadeh, R. Pace. “ new model λor μeneration-recombination in silicon depletion reμions aλter neutron irradiation. IEEE Transaction on Nuclear Science. .

[

] Z.D. Kovalyuk, V.N. Katerynchuk, O.“. Politanska, O.N. Sydor, V.V. Khomyak. Eλλect oλ μamma radiation on the properties oλ InSe photodiodes. Technical Physics Letters. – .

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] M. Vujisić. Simulated eλλects oλ proton and ion beam irradiation on titanium dioxide memristors. IEEE Transactions on Nuclear Science. – .

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] M. Vujisić, K. Stanković, E. Dolićanin, P. Osmokrović. Radiation hardness oλ COTS EPROMs and EEPROMs. Radiation Eλλects and Deλects in Solids Incorporatinμ Plasma Science and Plasma Technoloμy. – .

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] D.R. “lexander. Transient ionizinμ radiation eλλects in devices and circuits. IEEE Transaction on Nuclear Sciences. – .

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] D. Nikolić, “. Vasić-Milovanović, M. Obrenović, E. Dolićanin. Eλλects oλ successive μamma and neutron irradiation on solar cells. Journal oλ Optoelectronics and “dvanced Materials. – – .

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] D. Nikolić, “. Vasić, —. Lazarević, M. Obrenović. Improvement possibilities oλ the I-V characteristics oλ PIN photodiodes damaμed by μamma irradiation. Nuclear Technol‐ oμy & Radiation Protection. – .

[

] G.“.M. Hurkx, D.”.M. Klaassen, M.P.G. Knuvers. “ new recombination model λor device simulation includinμ tunnellinμ. IEEE Transactions on Electron Devices. – .

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] S. Palpacelli, M. Mendoza, H. J. Herrmann, S. Succi. Klein tunnelinμ in the presence oλ random impurities. International Journal oλ Modern Physics C. .

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] T.K. Kanμ, M.J. Chen, C.H. Liu, Y.J. Chanμ, S.K. Fan. Numerical conλirmation oλ inelastic trap-assisted tunnelinμ IT“T as SILC mechanism. IEEE Transactions on Electron Devices. – .

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] S. “ritome, R. Shirota, G. Hemink, T. Endoh, F. Masuoka. Reliability issues oλ λlash memory cells. Proceedinμs oλ the IEEE. – .

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] E. Rosenbaum, L. F. Reμister. Mechanism oλ stress-induced leakaμe current in MOS capacitors. IEEE Transaction on Electron Devices. – .

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] C.D. Younμ, G. ”ersuker, M. Jo, K. Matthews, J. Huanμ, S. Deora, K. “nμ, T. Nμai, C. Hobbs, P.D. Kirsch, “. Padovani, L. Larcher. New insiμhts into SILC-based liλe time extraction. IEEE International Reliability Physics Symposium IRPS . .

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] M. Razavy. Quantum Theory oλ Tunnelinμ. World Scientiλic Publishinμ Co. Pte. Ltd Sinμapore .

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] R. T. Collins, J. Lambe, T. C. McGill. Elastic and inelastic tunnelinμ characteristics oλ “l“s/Ga“s heterojunctions . Journal oλ Vacuum Science and Technoloμy ”. .

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] D.V. “verin, Y.V. Nazarov. Virtual electron diλλusion durinμ quantum tunnelinμ oλ the electric charμe. Physical Review Letters. .

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] L. Pelaz, J.L. Orantes, J. Vincente, L.“. ”ailon, J. ”arbolla. The Poole-Frenkel eλλect in H-SiC diode characteristics. IEEE Transactions on Electron Devices. – .

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] T. Goudon, V. Miljanović, C. Schmeiser. On the Shockley-Read-Hall Model Genera‐ tion-Recombination in Semiconductors. .

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] D. Nikolić, K. Stanković, Lj. Timotijević, Z. Rajović, M. Vujisić. Comparative study oλ μamma radiation eλλects on solar cells, photodiodes and phototransistors. International Journal oλ Photoenerμy. ID .

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] D. Nikolić, “. Vasić, I. Fetahović, K. Stanković, P. Osmokrović. Photodiode behavior in radiation environment. Scientiλic Publications oλ the State University oλ Novi Pazar Series “. – .

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.

Chapter 4

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends R. Deepalaxmi, V. Rajini and C. Vaithilingam Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62624

Abstract The survival oλ an electrical system is mostly μoverned by the endurance limit oλ the dielectric material employed in it. The λive diλλerent compositions oλ SiR–EPDM blends were prepared. Electron beam radiation has been widely used in the cable manuλactur‐ inμ industries in order to increase the liλe oλ the cable. Hence, the λive blends were irradiated to , and Mrad dose levels by electron beam accelerator. The dielectric parameters such as breakdown voltaμe ”DV , dielectric strenμth DS , dielectric constant DC , and dissipation λactor DF were measured as per “STM/IEC standards. This chapter evaluates the eλλect oλ electron beam irradiation on dielectric parameters oλ SiR–EPDM blends. Keywords: silicone rubber SiR , ethylene propylene diene monomer EPDM , break‐ down voltaμe ”DV , dielectric strenμth DS , dielectric constant DC , dissipation λac‐ tor DF , electron beam irradiation

. Introduction Electron beam irradiation has been eλλectively utilized in power cable industry and identi‐ λied as one oλ the most advanced processinμ techniques. The products processed with electron beam radiation, experience shorter exposure time, which could result in less oxidative eλλects on certain materials. It is essential to investiμate the eλλect oλ electron beam irradiation upon the dielectric parameters oλ the λive diλλerent compositions oλ SiR–EPDM blends [ – , ]. Hence, the samples oλ SiR–EPDM were irradiated to , and Mrad dose levels by electron beam accelerator. The new λunctional μroups λormed durinμ blendinμ and aλter the electron beam irradiation were investiμated throuμh physicochemical investiμation techniques like Fourier transλorm inλrared spectroscopy FTIR . To observe the morpholoμical chanμes and

94

Radiation Effects in Materials

also to identiλy the elemental composition, scanninμ electron microscope SEM analysis and enerμy dispersive X-ray analysis EDX“ were perλormed on SiR–EPDM blends. The eλλects oλ electron beam irradiation on the dielectric parameters oλ various compositions oλ SiR– EPDM blends were reported.

. Experimental . . Preparation of SiR–EPDM blends Commercially, available SiR and EPDM were used. Type oλ SiR-polydimethyl siloxane PDMS . The composition oλ EPDM is ethylene- % propylene- % diene monomer- %. Diene type is ethylidene norbornene EN” . They are supplied by M/S Joy Rubbers, India. The λive diλλerent compositions oλ SiR–EPDM blends were prepared [ – , ]. .

”lend “«SiR

%/EPDM

%.

.

”lend ”«SiR

%/EPDM

%.

.

”lend C«SiR

%/EPDM

%.

.

”lend D«SiR

%/EPDM

%.

.

”lend E«SiR

%/EPDM

%.

. . Electron beam irradiation The λive diλλerent compositions oλ SiR–EPDM blends were irradiated up to , and Mrad doses usinμ an electron beam accelerator oλ . MeV ratinμ at M/S Siechem Industries, Pondicherry, India.

. Characterization of SiR–EPDM blends . . Dielectric characterization In order to analyze the dielectric behavior oλ SiR–EPDM blends in harmλul environments, blends have been tested as per “STM/IEC standards. . . . Breakdown voltage and dielectric strength “s per standard “STM D IEC , ”DV and DS were measured. The sample dimen‐ sions oλ × × . cm were placed between two electrodes, and the voltaμe was increased at a λixed rate oλ V/s. The voltaμe at which dielectric breakdown occurs was measured as ”DV. DS was calculated.

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

. .2. Dielectric constant and dissipation factor DC and DF were measured as per “STM D were × × . cm.

IEC

at MHz. The sample dimensions

. . Physicochemical investigations Various physicochemical techniques such as FTIR, EDX“ and SEM were used to identiλy the nature oλ chanμes in the electron beam irradiated samples oλ SiR–EPDM blends. .2. . Fourier transform infrared spectroscopy FTIR analysis FTIR spectra oλ electron beam irradiated samples were taken usinμ Perkin Elmer spectropho‐ tometer, in the wave number ranμinμ λrom cm− to cm− . The number oλ scans λor each IR spectrum was . .2.2. Energy dispersive X-ray EDXA analysis EDX“ analysis has been perλormed usinμ EDX“ analysis setup Make HIT“CHI , in order to determine the elemental composition oλ the materials at the surλace oλ the electron beam irradiated samples oλ SiR–EPDM blends. .2. . Scanning electron microscopy SEM analysis SEM analysis was perλormed usinμ a scanninμ electron microscope Make HIT“CHI with a maμniλication oλ – , , in order to study the morpholoμy oλ the surλace oλ electron beam irradiated samples oλ SiR–EPDM blends.

. Results . . Dielectric characterization of virgin SiR–EPDM blends The virμin SiR rich blends “ and ” have hiμher breakdown voltaμe ”DV and dielectric strenμth DS , when compared to remaininμ blends. This may be due to the occurrence oλ maximum selλ cross-linkinμ durinμ the blendinμ process itselλ. Durinμ the blendinμ process, the cross-linkinμ reaction has taken place between the side chains oλ SiR and EPDM. The blend C and EPDM rich blends D and E were λound to have lesser values oλ ”DV, DS, and hiμher values oλ DC and DF in comparison with SiR rich blends “ and ” . . . Effect of electron beam irradiation on dielectric behavior of SiR–EPDM blends .2. . Effect on breakdown voltage and dielectric strength Figures and depict the variations in breakdown voltaμe and dielectric strenμth oλ λive diλλerent compositions oλ SiR–EPDM λor various doses oλ electron beam irradiation.

95

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Radiation Effects in Materials

Figure . Variations in breakdown voltaμe oλ SiR–EPDM blends λor various doses oλ electron beam irradiation.

Figure . Variations in dielectric strenμth oλ SiR–EPDM blends λor various doses oλ electron beam irradiation.

The ”DV and DS oλ SiR-rich blends “ and ” and EPDM-rich blends D and E reduced λor all doses oλ electron beam. The ”DV and DS oλ the blend C improved λor all doses oλ electron beam. The DC oλ the blend D and E has been improved at and / Mrad respectively. .2.2. Effect on dielectric constant and dissipation factor measurement Figures and depict the variations in dielectric constant and dissipation λactor oλ λive diλλerent compositions oλ SiR–EPDM blends λor various doses oλ electron beam irradiation.

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

Figure . Variations in dielectric constant oλ SiR–EPDM blends λor various doses oλ electron beam irradiation.

Figure . Variations in dissipation λactor oλ SiR–EPDM blends λor various doses oλ electron beam irradiation.

The DC oλ the blend “ reduced λor all doses oλ electron beam. The DC oλ blend ” reduced at and Mrad. The DF oλ SiR-rich blends “ and ” reduced λor all doses oλ electron beam. The DC and DF oλ the blend C improved at and Mrad respectively. The blend D has the improved DF at Mrad.

97

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Radiation Effects in Materials

. Discussion . . Dielectric performance of virgin and electron beam irradiated SiR–EPDM blends For SiR–EPDM blends, it has been observed that cross-linkinμ and chain scission may modiλy the macromolecular chains oλ the material. The consequence is the chanμe in the dielectric parameters oλ the material. The eλλect oλ dominant mechanism can be noted λrom the chanμes in dielectric parameters. . . FTIR analysis FTIR spectra oλ electron beam irradiated samples oλ SiR–EPDM blends were obtained to identiλy the mechanism λor the chanμe in dielectric parameters aλter the electron beam irradiation. FTIR spectra oλ the virμin and electron beam irradiated samples oλ three compo‐ sitions oλ SiR–EPDM blends are depicted in Figures – respectively.

Figure . FTIR spectra oλ electron beam irradiated samples oλ blend “. a

Mrad, b

Mrad and c

Mrad.

The FTIR investiμations on electron beam radiated samples revealed that the radiation has induced the chemical and morpholoμical chanμes. The variation in dielectric parameters was validated throuμh FTIR spectra. It depicts the occurrence oλ new λunctional μroups alonμ with the % absorbance and the correspondinμ wave number. Tables and list the correlation oλ variation in dielectric parameters oλ electron beam irradiated samples oλ SiR rich blends and EPDM rich blends and blend C usinμ FTIR respectively.

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

Figure . FTIR spectra oλ electron beam irradiated samples oλ blend C. a

Mrad, b

Mrad and c

Mrad.

Figure . FTIR spectra oλ electron beam irradiated samples oλ blend E. a

Mrad, b

Mrad and c

Mrad.

99

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Radiation Effects in Materials

Behavior of

Mrad

Mrad

Mrad

dielectric parameter/doses ” → Improvement

“lcohol OH

in DC at

bonded, stronμ, broad “ →

Mrad

“lcohol OH bonded, stronμ,

broad

”→

“→

cm−

with

%

cm− with

cm− with

%

cm− with

%

“→

cm− with

%

”→

cm− with

%

Si–O–Si

Si–o–Si

”→

“lcohol OH bonded, stronμ, broad %

“→

cm− with

%

”→

cm− with %

“→

cm− with %

”→

cm− with

%

Si–O–Si “→ cm− with ”→ with Reduction in ”DV,

%

cm− %

“bsence oλ alcohol OH -λree, stronμ, sharp μroup and acid COOH μroup

DS and DF “ → Reduction in DC Table . Correlation oλ variation oλ dielectric parameters oλ electron beam irradiated samples oλ SiR rich blends usinμ FTIR.

The ”DV, DS, and DF oλ the SiR rich blends “ and ” λound to reduce λor all doses oλ electron beam irradiation. This is due to the disappearance oλ acid COOH μroup in them. The ”DV and DS oλ the blend C is improved λor all doses oλ electron beam irradiation. This is due to the appearance oλ Si–O–Si μroup at , , and cm− with , , and % absorbance in it. The dielectric constant is improved at Mrad. This may be due to the appearance oλ =C–H “lkene, bendinμ, stronμ . The DF has been reduced at Mrad. This may be due to the disappearance oλ =C–H “lkene, bendinμ, stronμ . The maximum improvement in DC oλ blend D occurred at Mrad. This may be due to the increase in Si–O–Si μroup at cm− with % absorbance and also due to the shiλtinμ oλ alcohol OH -λree μroup to hiμher wave number [ – ]. The maximum improvement in DC oλ blend E has occurred at Mrad. This may be due to the increase in alcohol OH -λree μroup at cm− with % absorbance. Behavior of dielectric parameter/

Mrad

Mrad

Mrad

doses C

“bsence oλ =C–H “lkene , Improvement in

=C–H “lkene , bendinμ

Improvement in ”DV, DS

bendinμ stronμ

stronμ at

Improvement in DF except at

Mrad D →

%

Si–O–Si μroup cm−

at

Improvement in DC at Mrad

cm− with

%

C–H alkane μroup at

EPDM rich blends D and E

cm− with

“bsence oλ =C–H

“lcohol OH λree,

cm− with

%

“lcohol OH bonded, stronμ,

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

Behavior of dielectric parameter/

Mrad

Mrad

Mrad

doses D→ DC except at

“lkene , bendinμ /

stronμ, sharp

stronμ

D→

Mrad Improvement in

Increase in

with

DF except at /

Si–O–Si

E→

E → Improvement in

Mrad

μroup at

with

DC except at

cm− with

Mrad

%

cm−

broad with %E→

cm− with

%

% cm− %

“lcohol OH bonded,

absorbance

stronμ, broad

*Shiλtinμ oλ

D→

alcohol O–H

with

λree μroup to

E→

hiμher wave

with

cm− % cm− %

number Table . Correlation oλ variation oλ dielectric parameters oλ electron beam irradiated samples oλ EPDM rich blends and blend C usinμ FTIR.

. . EDXA analysis Figures – show the EDX“ curves oλ the electron beam irradiated samples oλ blends “, C, and E respectively. The inλerences λrom EDX“ curves oλ all the irradiated samples oλ SiR– EPDM blends are listed in Tables and .

Figure . EDX“ curves oλ electron beam irradiated samples oλ blend “. a

Mrad, b

Mrad and c

Mrad.

101

102

Radiation Effects in Materials

Figure . EDX“ curves oλ electron beam irradiated samples oλ blend C. a

Figure

. EDX“ curves oλ electron beam irradiated samples oλ blend E. a

Mrad, b

Mrad, b

Mrad and c

Mrad and c

Mrad.

Mrad.

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

Doses/elements

Carbon wt % A

Silicon wt % B

A

Oxygen wt % B

Mrad

.

.

.

Mrad

A

.

B .

.

.

.

.

.

.

.

Mrad

.

.

.

.

.

.

Mrad

.

.

.

.

.

Table . Inλerences λrom EDX“ curves oλ electron beam irradiated samples oλ SiR rich blends “ and ” .

Doses/elements

Carbon wt % C

D

Silicon wt % E

Oxygen wt %

C

D

E

D

E

.

.

.

.

.

.

.

.

.

.

.

.

.

Mrad

.

.

.

.

.

.

Mrad

.

.

.

.

.

.

Mrad

.

.

.

.

Mrad

.

.

.

.

.

C .

Table . Inλerences λrom EDX“ curves oλ electron beam irradiated samples oλ EPDM rich blends D and E and blend C.

. . Correlation of EDXA results with FTIR The interpretations between EDX“ and FTIR oλ the electron beam irradiated samples oλ SiR– EPDM blends are listed in Tables – .

Inference from

Mrad

Mrad

Mrad

EDXA Increase in carbon content

C=C alkene, stretch

C=C alkene, stretch

C=C alkene, stretch

variable /C=C

variable /C=C

variable / /=C–H

asymmetric, stretch,

asymmetric, stretch,

stronμ /C–H

stronμ /C–H

alkane /=C–H

alkene bendinμ stronμ

alkane

alkene bendinμ stronμ Decrease in silicon content

Presence oλ Si–O–Si/Si–CH –CH and Si–H

except at Mrad Increase in oxyμen content

Increase in “lcohol –OH λree μroup content

except Mrad

Occurrence oλ Si–O–Si μroup

Table . Interpretation between EDX“ and FTIR oλ the electron beam irradiated samples oλ blend “.

103

104

Radiation Effects in Materials

Inference from EDXA

Mrad

Mrad

Increase in carbon

Increase in CH –CH –CH

content

“ppearance oλ C=C asymmetric, stretch,

Mrad

“ppearance oλ C–H alkane , “ppearance oλ C=C asymmetric, bendinμ ,stronμ

stretch, stronμ /C–H alkane ,

stronμ

bendinμ, stronμ/=C–H alkene , bendinμ, stronμ

Decrease in silicon

“bsence oλ Si–H amorphous Si

content except at Mrad Decrease in oxyμen

“bsence oλ acid COOH μroup

content Table . Interpretation between EDX“ and FTIR oλ the electron beam irradiated samples oλ blend C.

Inference from EDXA Decrease in carbon content Increase in silicon content

Mrad

Mrad

Mrad

“bsence oλ acid –COOH μroup “ppearance oλ Si–H

Increase in Si–CH –CH /Si–H content

amorphous Si Increase in Si–CH – CH /Si–H content Increase in oxyμen content

Increase in alcohol –OH -λree μroup content

Table . Interpretation between EDX“ and FTIR oλ the electron beam irradiated samples oλ blend E.

. . SEM analysis Figure a , b , c , d , e and a , b , c , d , e are the SEM microμraphs oλ the electron beam irradiated samples oλ SiR–EPDM blends exposed to Mrad dose oλ electron beam irradiation λor a maμniλication oλ and respectively. Figure a , b , c , d , e and a , b , c , d , e are the SEM microμraphs oλ the electron beam irradiated samples oλ SiR–EPDM blends exposed to Mrad dose oλ electron beam irradiation λor a maμniλication oλ and respectively. It is observed λrom Figure a , a that the surλace oλ SiR rich blend “ has larμer number oλ cracks. This may be due to the decrease in silicon content λor Mrad dose oλ electron beam irradiation inλerred λrom EDX“ analysis , but the surλace oλ blend ” and EPDM rich blends D and E has smaller number oλ cracks. This is validated throuμh the increase in oxyμen and silicon concentrations inλerred λrom EDX“ analysis . The surλace oλ blend C has smaller cracks. This may be due to the reduction in oxyμen and silicon concentrations. The availability oλ white particles on the surλace oλ the blends ”, D, and E may be due to the decrease in carbon content in them inλerred λrom EDX“ curves .

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

Figure . SEM microμraphs oλ electron beam irradiated c , d and e maμniλication a , b ,

Mrad samples oλ SiR–EPDM blends. a , c , d and e maμniλication.

b ,

Figure . SEM microμraphs oλ electron beam irradiated c , d and e – maμniλication a , b ,

Mrad samples oλ SiR–EPDM blends. a , c , d and e – maμniλication.

b ,

105

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Radiation Effects in Materials

It is observed λrom Figure a , b that the surλace oλ SiR rich blend “ has larμe number oλ cracks. This may be due to the decrease in silicon content λor Mrad dose oλ electron beam irradiation inλerred λrom EDX“ analysis , but the surλace oλ blend ” and EPDM rich blends D and E has smaller number oλ cracks. This is validated throuμh the increase in oxyμen and silicon concentrations λrom EDX“ analysis. The surλace smoothness oλ blend C is moderate. This may be due to the reduction in oxyμen and silicon concentrations.

. Conclusion The blend C is λound to have the improved ”DV and DS values λor all doses oλ electron beam irradiation. “lso a siμniλicant improvement in DC has been noticed at Mrad in blends C, D, and at and Mrad in blend E respectively. “ considerable improvement in DF has been observed at and Mrad in blend C and at Mrad in blend D respectively. Hence, it is concluded that blend C and EPDM rich blends are λound to have improved dielectric per‐ λormance aλter the electron beam exposure.

Acknowledgements The authors μrateλully acknowledμe the λinancial support extended by SSN Colleμe oλ Enμineerinμ λor carryinμ out this research work.

Author details R. Deepalaxmi *, V. Rajini * and C. Vaithilinμam

*

*“ddress all correspondence to [email protected] *“ddress all correspondence to [email protected] *“ddress all correspondence to [email protected] Department oλ EEE, SSN Colleμe oλ Enμineerinμ, Chennai, Tamilnadu, India SELECT, VIT University, Chennai, Tamilnadu, India

References [ ] R. Deepalaxmi, M. ”alaji and V. Rajini, Particle Swarm Optimization ”ased Selection oλ Optimal Polymeric ”lend, IEEE Trans. Dielectr. Electr. Insul., , Vol. , No. , pp. – .

Electron Beam Irradiation Effects on Dielectric Parameters of SiR–EPDM Blends http://dx.doi.org/10.5772/62624

[ ] R. Deepalaxmi and V. Rajini, Perλormance Evaluation oλ Electron ”eam Irradiated SiREPDM ”lends, IEEE Trans. Dielectr. Electr. Insul., , Vol. , No. , pp. – . [ ] R. Deepalaxmi and V. Rajini, Perλormance Evaluation oλ Gamma Irradiated SiR-EPDM ”lends, Nucl. Enμ. Des. Elsevier , , Vol. , pp. – . [ ] R. Deepalaxmi and V. Rajini, Property Enhancement oλ SiR-EPDM ”lend Usinμ Electron ”eam Irradiation, Int. J. Electr. Enμ. Technol., , Vol. , No. , pp. – . [ ] V. Rajini and K. Udayakumar, Deμradation in Silicone Rubber under “C or DC Voltaμes in Radiation Environment, IEEE Trans. Dielectr. Electr. Insul., , Vol. , No. , pp. – . [ ] V. Rajini and K. Udayakumar, Resistance to Trackinμ oλ EPDM “μed by Gamma Irradiation under “C and DC Voltaμes, Int. J. Emerμ. Electr. Power Syst., , Vol. , No. , pp. – . [ ] R. Hackam, Outdoor HV Composite Polymeric Insulators, IEEE Trans. Dielectr. Electr. Insul., , Vol. , No. , pp. – . [ ] M. ”rown, Compoundinμ oλ Ethylene Propylene Polymers λor Electrical “pplications, IEEE Electr. Insul. Maμ., , Vol. , No. , pp. – . [ ] R. Raja Prabu, S. Usa and K. Udhyakumar, Electrical Insulation Characteristics oλ Silicone and EPDM ”lends. IEEE Trans. Dielectr Electr. Insul., , Vol. , No. , pp. – . [

] M. Ehsani, H. ”orsi, E. Gockenbach, G.R. ”akhshande, I.J. Morshedian and I.N. “bedi, Study oλ Electrical, Dynamic Mechanical and Surλace Properties oλ Silicone-EPDM ”lends, IEEE Int. Conλ. Solid Dielectr., Toilouse, France, , pp. – .

[

] S. Kole and K. Tripathy, Morpholoμy and “μeinμ ”ehaviour oλ Silicon-EPDM ”lends, J. Mater. Sci., , pp. – .

[

] P.D. ”lackmore, D. ”irtwhistle, G.“. Cash and G.“. Georμe, Condition “ssessment oλ EPDM Composite Insulators usinμ FTIR Spectroscopy, IEEE Trans. Dielectr. Electr. Insul., , Vol. , No. , pp. – .

[

] M. Celina, K.T. Gillen, J. Wise and R.L. Clouμh, “nomalous “μinμ Phenomena in the Cross Linked Polyoleλin Cable Insulation, I“E“-TECDOC, Radiat. Phys. Chem., , Vol. , pp. – .

[

] W. “rayapranee and G.L. Rempel, Properties oλ NR/EPDM ”lends with or without Methyl Methacrylate-”utadiene-Styrene M”S as a Compatibilizer, Int. J. Mater. Struct. Reliab., , Vol. , No. , pp. – .

[

] S. Simmons, M. Shah, J. Mackvich and R.J. Chanμ, Polymeric Outdoor Insulatinμ Materials, Part-III-Silicone Elastomer Consideration, IEEE Electr. Insul. Maμ., , Vol. , No. , pp. – .

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[

] Z. Tvaaruzkova and V. ”osacek, Characterization oλ Hydroxyl Groups oλ Y Zeolites by Inλrared Spectra, Chem. Zvesti, , Vol. , No. , pp. – .

[

] “.M. Shehap, Thermal and Spectroscopic Studies oλ Polyvinyl “lcohol/Sodium Carboxy Methyl Cellulose ”lends, Eμypt. J. Solids, , Vol. , No. , pp. – .

[

] ”.Saikia and G. Parthasarathy, Fourier Transλorm Inλrared Spectroscopic Characteri‐ zation oλ Kaolinite λrom “ssam and Mehalaya, Northern India, , J. Mod. Phys., Vol. , pp. – .

Chapter 5

Radiation and Environmental Biophysics: From Single Cells to Small Animals Yanping Xu Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62623

Abstract In this chapter, two oλ very unique and novel radiation technoloμies λor modern radiobioloμy studies are reviewed. First oλ all, it is concentrated on the developments oλ accelerator-based particle microbeam system, which has been eλλectively used λor studyinμ the puzzle oλ radiation-induced bystander eλλect.€ In addition, a recent published sinμlecell microbeam study, which is aiminμ to directly measure a cell’s radio-sensitivity combininμ microbeam system with selλ-reλerencinμ biosensor, is included. Then, toward the study oλ realistic irradiation scenarios in radiation bioloμy in particular, such as a nuclear attack λor homeland security concerns or a potential larμe-scale radioloμical event, there would be a major need to ascertain, within a λew days, the radiation doses received by tens or hundreds oλ thousands oλ individuals. Speciλically, bioloμical tests would need to be established to estimate the likelihood oλ such radiation exposure to result in serious health consequences tests that would then be applied to decide on the correct treat‐ ments that miμht mitiμate the short- and lonμ-term health eλλects oλ such radiation exposure. However, because oλ the complexity and diλλiculty oλ conductinμ tests in such circumstance, innovative irradiation systems and technoloμy are required. So the new developments oλ small animal irradiation system λor evaluatinμ the radiation risk and carryinμ out animal model radiobioloμy experiments within the mimicked radiation scenarios are covered in the second halλ oλ this chapter. Keywords: Microbeam, Micro-biosensor, Sinμle-cell irradiation, Small animal irradia‐ tion, “ccelerator

. Introduction Historically, cancer and other health risks stemminμ λrom exposure to low-level radiation have been diλλicult to evaluate due to the hiμh spontaneous λrequency oλ aμe-related cancer and

112

Radiation Effects in Materials

deμenerative diseases. With the dramatic increase in exposure oλ the human population to lowdose radiation either λrom diaμnostic procedures, industrial applications, mininμ, cleanup oλ contaminated sites, and space travel, there has been a μreat scientiλic need λor better estimates oλ the risks to such exposures. One oλ the drivinμ λorces behind the low-dose radiation re‐ search is developinμ specialized radiation technoloμy and novel, versatile biophysics tools λor such radiation bioloμy and radiation physics studies.

. Single-cell microbeam irradiation . . Microbeam For low-dose radiation circumstances which are extremely relevant to the environmental radiation exposure, individual cells hardly experience traversals by radiation particles. The bioloμical eλλects oλ such low-dose radiation are unknown, and it is very diλλicult to study with conventional broad radiation beam exposure due to Poisson distribution oλ tracks. “lso the cell-to-cell communication cannot be addressed directly because oλ the random radiation oλ broad beam particles. The microbeam system can overcome these diλλiculties. Microbeam is an irradiation system which delivers a certain number oλ particles with a micron-sized diameter spot to a chosen bioloμical tarμet, which allows damaμe to be precisely deposited within speciλic locations e.μ., nuclei or cytoplasm oλ sinμle cells . Charμed particle microbeams have been siμniλicant contributions to deλininμ the bioloμical tarμets oλ ionizinμ radiations. “lso with microbeam, cell nuclear and cytoplasmic responses oλ tarμeted cells are established alonμ with the responses oλ non-tarμeted bystander cells [ ]. There is evidence that radiationinduced bystander siμnals between cells may oriμinate with a diλλusible mediator [ – ]. For more than years, the Radioloμical Research “ccelerator Facility R“R“F oλ Columbia University has built and operated a charμed particle microbeam λacility capable oλ irradiatinμ the nuclei oλ individual bioloμical cells with as λew as one helium ion or proton [ , ]. The R“R“F microbeam II is an updated system, and it is driven by a . MV HVEE Sinμleton “ccelerator. The particles are ionized by a radio-λrequency RF ion source inside the Sinμleton “ccelerator and are accelerated λrom a DC hiμh-voltaμe terminal to reach the desired enerμy. Then, the particle beam passes throuμh a beam transport system to the beam end station where irradiation experiments take place. The beam transport system includes a λew beam manipu‐ lation elements Figure . The main beam slits and beam stop are used to eliminate unwanted ion beams, to limit the size oλ the beam enterinμ a ° bendinμ maμnet, and to stop the beam λrom enterinμ the bendinμ maμnet when irradiations are not expected. The maμnetic steerinμ maμnet is used to make λine adjustments, aiminμ the ion beam at the entrance oλ the bendinμ maμnet. The ° bendinμ maμnet is used to bend the beam into the vertical direction. The beam deλlector/shutter is an electrostatic system that steers the beam rapidly ~ ms to end the irradiation oλ a cell. The object aperture ~ μm diameter limits the initial beam size. “ custom built electrostatic double-quadrupole triplet system [ ] is used to λocus the beam at the position oλ the cells to be irradiated. In λront oλ the λirst triplet lens, an anμular limitinμ aperture is used to eliminate particles enterinμ at larμe anμles to help reduce the diameter oλ the beam spot.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

The beam exit window is a thin silicon nitride λoil attached to a stainless steel disk, with thickness oλ either nm or nm λor a sub‐micron beam spot to minimize scatterinμ the beam. The cell dish holder is desiμned to locate cells at the λocusinμ plane oλ the microbeam and is in the view ranμe oλ a customized microscope. “n imaμinμ/tarμetinμ system comprises a precision XYZ staμe MadCity Labs, Inc. WI , a Nikon Eclipse E microscope, and an attached PhotonM“X” EMCCD camera Princeton Instruments, NJ . This equipment combination also allows us to imaμe the wide ranμe oλ λluorescent proteins that have been developed. “ computer control proμram written in Visual ”asic locates the cells, plated in a cell culture dish, and positions them λor irradiation. While the R“R“F microbeam is primarily used λor charμe particle irradiation, the accelerator can be used as source λor neutral particle radiation, λor example, neutron radiation [ – ].

Figure . R“R“F microbeam.

. . Single-cell microbeam irradiation with oxygen micro-biosensor To physically demonstrate the radiation-induced oxyμen λlux chanμes outside the irradiated cell, a selλ-reλerencinμ amperometric electrochemical sensor was proposed λor use with sinμlecell microbeam irradiation experiment. This type oλ micro-biosensor allows sensitive and noninvasive measurement oλ the λlux oλ radical mediators, such as oxyμen or nitric oxide , in sinμle cells. This is achieved by repeatedly movinμ the micro-biosensor/probe tip throuμh the extracellular μradient at a known λrequency and a known distance apart. This so-called selλreλerencinμ technique minimizes the measurement challenμes caused by the random driλt oλ the sensor output. In conjunction with a microbeam, it has the capacity to accurately detect selected ionic and molecular μradient chanμes surroundinμ a sinμle cell with hiμh spatial

113

114

Radiation Effects in Materials

resolution. The λirst radiobioloμy experiment was to analyze metabolic oxyμen consumption in individual livinμ lunμ cell aλter sub-cellular irradiation and to explore the radiation response oλ such cells. The selλ-reλerencinμ oxyμen electrochemical system was developed at the ”ioCurrents Shared Resource at the Marine ”ioloμical Laboratory M”L , Woods Hole, M“. It was inteμrated with the R“R“F sinμle-particle, sinμle-cell microbeam to λorm a sinμle-cell irradiation response detection platλorm. . . Oxygen self-referencing micro-biosensor Selλ-reλerencinμ polaroμraphic SERP micro-sensor technoloμy was developed at the ”ioCurrents Shared Resource [ – ]. These sensors are made oλ borosilicate μlass capillaries ” , WPI which are pulled to outer tip diameters oλ ~ μm usinμ a Sutter PSutter Instrument, C“ . Then, a -μm diameter μold wire “lλa “esar, Ward Hill, M“ is electro‐ chemically etched in an aqueous solution oλ N HCl to reduce the tip diameter to ~ μm. “λter beinμ rinsed with water and isopropyl alcohol, the etched “u wire is inserted into the capillary so that the wire protrudes sliμhtly λrom the pipette tip. The electrode tip is dipped into UV curinμ epoxy , Dymax, Torrinμton, CT . The exposed “u electrode is then etched aμain same conditions as above to λorm a recessed electrode with a cavity – μm deep. Finally, the electrode is coated by dippinμ it in a solution oλ % cellulose acetate kDa λor s and dryinμ λor – min. The electrochemical sensor itselλ is attached to a ”RC amperometric head staμe via a modiλied ”NC connecter. “n L-shaped “μ/“μCl reλerence electrode, connected via a M KCl/ % aμar bridμe reλerence probe placed in the bulk solution, completes the circuit Figure . Selectivity λor amperometric electrodes is usually deλined by the conditioninμ, operatinμ voltaμe, and excludinμ membranes.

Figure . Selλ-reλerencinμ micro-biosensor detection system.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

. . System integration For sinμle-cell irradiation response measurements, sensor access durinμ and aλter irradiation λor precision location oλ damaμe within sinμle cells with the imaμinμ system is crucial. Microprobe measurements without irradiation are usually perλormed on an inverted micro‐ scope μivinμ open access λrom above λor probe placement. With microbeam irradiation, there is a constraint λrom the exit window below the sample, so microscopy and probinμ must be done λrom above the sample. “ccess requires that the tip oλ the probe microelectrode approaches a sinμle cell, at an anμle oλ between ° and °, to within microns oλ the plasma membrane. “ccess λor the reλerence electrode is also required. ”oth the measurinμ probe and the reλerence electrode have body diameters oλ . mm, while the measurinμ tip is drawn to a point. “ Nikon × lonμ workinμ distance mm dry microscope objective is placed with the probe in a sample dish. ”ecause the probe approach anμle is so severely constricted, the anμle settinμ technique appropriate λor an open-access system is completely inadequate. “n oλλset hinμe manipulator was desiμned Figure and built which allows rapid repeatable reposi‐ tioninμ oλ the probe and simple anμle adjustments. The hinμe was constructed in a stacked conλiμuration usinμ hiμh-precision λlex pivots in such a way that anμular settinμs between ° and ° can be set. In order to use the manipulator and the stacked hinμe to satisλy our needs, a universal mountinμ car Thorlabs, NJ ridinμ on an optical rail with an inteμrated robotic retraction mechanism is used. The probe manipulators are mounted accurately on the car λor simple interchanμe. This robotic manipulator structure and the associated λully inteμrated control systems allow us to meet all the micromanipulation, and capillary probe placement needs in an eλλicient manner. . . Measurement 2.5. . Cell preparation The human telomerase reverse transcriptase hTERT immortalized human small airway epithelial S“E cells were thawed λrom liquid nitroμen and cultured in λresh medium. Cells were diluted in λresh medium, and cultured cells were maintained at °C in a humidiλied %

Figure . Electrochemical micro-sensor mounted on microbeam end station by the oλλset hinμe system.

115

116

Radiation Effects in Materials

CO incubator. The microbeam cell culture dishes were custom-made λor cell μrowth and cell irradiation. They are made oλ Falcon mm Petri dish, and a . -inch diameter hole is drilled into the center oλ the dish bottom. The polypropylene λilm covered on the bottom oλ microbeam dish wells was treated with Cell-Tak ”D ”iosciences to enhance cell attachment. “lso it allows the chosen radiation to μet throuμh to the cells while allowinμ them to be placed upriμht on the microbeam end stations with minimal distance between the dish bottom and beam exit window. Dishes were incubated at °C λor min and were then rinsed. Then, the cells were trypsinized and diluted to . × /ml about cells in a total volume oλ μl medium . “ sterile – mm square coverslip covered the well aλter cells in a droplet were plated usinμ a micropipetter as close as possible to the center oλ the dish. The dishes were placed in an incubator until cells attached to the polypropylene. “λter cell attachment, the coverslips were removed and ml more oλ medium was replenished to the dishes. Cells will typically λlatten out within – h. The cells were stained by exposure to a nM solution oλ the vital DN“bindinμ stain Hoechst λor min prior to radiation. This low stain concentration necessitates the use oλ an EMCCD camera Princeton Instrument to obtain a hiμh-contrast imaμe and allows rapid location oλ the cell nuclei to be hit, or not hit, as the experiment calls λor durinμ irradiation. 2.5.2. Radiation beam setup ”eam size and beam location were measured with a nickel kniλe edμe scan [ ]. ”eam location was reμistered usinμ scanninμ oλ λluorescent beads. This was done by placinμ a microbeam dish containinμ λluorescent beads on the staμe. Then, an isolated bead was moved to the approximate beam position. “ spiral enerμy loss mappinμ scan was conducted with a solidstate charμe particle detector. Once the center oλ the beam was identiλied, the bead was moved to that position the center oλ beam mappinμ and the beam location was reμistered with the imaμinμ system. The low-maμniλication pictures oλ the bead were taken, and a center‐oλ‐

Figure . Measurement setup on microbeam end station.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

μravity proμram routine was used to transλer the bead coordinates to the computer. Then, the cell dish was removed λrom incubator and was mounted on the microbeam staμe. The chosen cell was moved to the reμistered beam position with an XYZ staμe MadCity Labs, Inc. WI , while monitored with a Nikon Eclipse E microscope and a reλerence picture was taken with an attached EMCCD camera Figure . Then, the micro-electrochemical sensor and reλerence electrode were mounted on the XYZ staμe, and the sensor/probe was careλully moved close to the cytoplasm about – μm away monitored with a Nikon × objective lens, and a backμround/control measurement was run λor about min with the sensor moved rapidly between two positions μm apart at a λrequency oλ . Hz. Data were collected at each pole position λor approximately s or % oλ the cycle time. The current siμnals were averaμed at each position, and then, a diλλerential current was obtained that can be converted into a directional measurement oλ λlux usinμ the Fick equation. Reλerencinμ the siμnals in this manner has the advantaμe that sources oλ interλerence caused by random driλt and noise are eλλectively λiltered λrom the siμnal and λluxes can be monitored in real time. 2.5. . Radiation and real-time oxygen consumption measurement Durinμ the sinμle-cell microbeam irradiation, the current chanμes were monitored with biosensor in selλ-reλerencinμ mode. The number oλ helium ions was set at or in the microbeam irradiation protocol λor this sinμle-cell irradiation. The particle beam count rate was measured at about per second. “ pulser Ortec Inc, TN was used to simulate the real count rate and to control the beam shutter, because the . MeV helium ions cannot pass all the way throuμh the cell and the medium ~ mm thick without beinμ absorbed. In the cytoplasm irradiation experiments, an exclusion zone around each λluorescinμ nucleus is automatically μenerated to ensure that the cytoplasm tarμet positions λrom one cell are not accidentally within the nucleus oλ an adjacent cell. Mutation induction caused by cytoplasmic irradiation has been reported usinμ this technique. The imaμe analysis system deλines the lonμ axis oλ each cell nucleus, aλter which the computer system delivers particles at two tarμet positions alonμ this axis, μm away λrom each end oλ the cell nucleus. Durinμ the experiment, an in-house code with Matrox Genesis imaμinμ library has been used to handle the imaμes subtract backμround, correct λor illumination variation, locate cells, and record location oλ nearest λrame . . . Results To detect physioloμically driven molecular movements around the cell membrane, which is normally very small λ“ current , the driλt and backμround have to be taken care oλ with selλreλerencinμ technique. This requires extractinμ small electrical siμnals, λ“ diλλerences “C on top oλ larμe oλλset siμnals s oλ p“ DC . With cells exposed to μM anti-mycin, the basal cellular O λlux was tested and the chanμes in oxyμen concentration dependent current DC chanμes were detected. Then, both cytoplasm and nucleus irradiations with % cell radiation were conducted. Figure shows the backμround and driλtinμ DC durinμ the radiation. “ very obvious O current chanμe “C was recorded within seconds aλter cyto‐ plasm irradiation. Figure shows the “C current chanμe λrom two measurements with two

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Figure . Selλ-reλerencinμ oxyμen ion–selective probe result with alpha microbeam irradiation DC .

diλλerent probes. The small chanμes in oxyμen consumption could be extracted λrom the backμround oxyμen concentration with the selλ-reλerencinμ method. “ similar but relative small chanμe was observed aλter nucleus irradiation. Without radiation, any oλ these larμe spikes cannot be seen on a lonμ-time backμround measurement. Twelve measurements were conducted resultinμ in a success rate oλ ~ % as determined by the individual cell λlux test because oλ the cell-to-cell variations and the uncertainty oλ the probe locations. The results indicate a role λor mitochondrial damaμe λollowinμ irradiation and enable λurther evaluations oλ the radiation-induced bystander eλλect. This eλλect is hypothetically due to the result oλ damaμe siμnals received by non-hit cells λrom hit cells. Establishinμ the mechanistic basis λor such responses in the λorm oλ damaμe siμnalinμ λrom hit to non-hit cells and continued siμnalinμ has proven to be elusive. However, evidence λor both oxyμen- and nitroμen-based small molecules and mitochondrial dysλunction has been produced. The approach outlined in this study suμμests biosensor mediators in the λorm oλ oxyμen radicals, nitric oxide, and hydroμen peroxide can be directly measured at a sinμle-cell level in both hit cells and bystander cells providinμ an incisive method oλ evaluatinμ such evidence. This establishment oλ a noninvasive, selλ-reλerencinμ biosensor/probe system in conjunction with the R“R“F microbeam provides an additional means λor probinμ bioloμical responsiveness at the level oλ individual cell, aλter precise sub-cellular tarμetinμ in hit cells and bystander cells.

. An accelerator-based neutron small animal irradiation facility . . Overview of IND-related radiation protection Several scenarios oλ larμe-scale radioloμical events include the use oλ an improvised nuclear device IND that may produce a siμniλicant neutron component with the prompt radiation exposure [ ]. Speciλically, the prompt radiation λrom this type oλ detonation is expected to be qualitatively similar to that oλ the μun-type kT device exploded over Hiroshima [ ]. In order to assess the siμniλicance oλ the neutron exposure in dose reconstruction λor this type oλ scenario and to allow characterization oλ novel neutron-speciλic biodosimetry assays, a new broad-enerμy neutron irradiator was desiμned [ ] at the Columbia University R“R“F.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

This accelerator-driven neutron irradiator provides a broad-spectrum neutron λield with enerμies λrom . to MeV that mimics the evaluated enerμy spectrum produced in the detonation oλ the atomic bomb at Hiroshima at – . km distance λrom μround zero [ ]. “t this distance, both survival and radiation exposure are expected to be suλλiciently hiμh to require triaμe λor allocation oλ medical eλλorts based on the Hiroshima data, the most survivors around this distance receive an appreciable neutron dose up to . Gy [ ] . However, the spectrum observed at this distance is siμniλicantly diλλerent λrom a standard reactor spectrum due to transport in the air, and has a larμer component oλ low-enerμy neutrons. It is expected that this diλλerence would have a siμniλicant impact on biodosimetric dose reconstruction. The neutron λield is produced by a mixed beam and composed oλ MeV atomic and molecular ions oλ hydroμen and deuterium that is used to bombard a thick beryllium ”e tarμet. The latter is a well-known neutron-producinμ material not only because oλ its hiμh neutron yield but also because oλ its stability and hiμh speciλic heat. This mixed beam produces a neutron spectrum which is the sum oλ the spectra λrom the ”e d,n ” and ”e p,n ” reactions λor all the incident ions monatomic, diatomic and triatomic and λor enerμies λrom MeV and down. In μeneral, λor monatomic MeV projectiles, the ”e d,n ” reaction provides a spectrum with hiμher-enerμy neutrons above MeV , while the ”e p,n ” reaction primarily yields neutrons below MeV. These nuclear reactions μenerate a combined neutron spectrum with a wide ranμe oλ enerμies, which can then be used to irradiate bioloμical samples and small animals e.μ., mice λor radiobioloμy studies. The beam composition in the present setup is approximately a ratio oλ protons to deuterons. However, λor other scenarios, the spectrum shape can be modiλied by adjustinμ the ratio oλ protons to deuterons and the incident beam enerμy. “s described elsewhere [ ], the neutron spectra were evaluated by makinμ combined measurements with a proton-recoil proportional counter [ ] and liquid scintillator detector [ ]. The measured recoil spectra were unλolded usinμ maximum entropy deconvolution [ ], based on Monte Carlo simulated detector response λunctions [ ]. The dosimetry λor the irradiations was perλormed usinμ a custom tissue-equivalent TE μas ionization chamber, placed on the sample holder wheel. This chamber measures the total dose

Figure . Selλ-reλerencinμ oxyμen ion-selective probe result with alpha microbeam irradiation “C .

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in the mixed neutron and γ-ray λield. To evaluate the ratio oλ neutron and γ doses, μammaray dosimetry was perλormed separately by replacinμ the ionization chamber with a compen‐ sated Geiμer–Mueller dosimeter, which has a very low neutron response [ ]. These measurements indicated that all neutron exposures, usinμ this spectrum, are accompanied by a parasitic photon dose oλ about % oλ the total dose delivered. In order to account λor possible variations in the dose rate durinμ irradiations, a second TE μas ionization chamber is placed in a λixed location on the beam axis, directly downstream oλ the neutron tarμet and used as a monitor. “ll measurements are normalized to the siμnal λrom the monitor, which is used to determine the dose durinμ irradiation. In a realistic scenario, it is expected that the neutron dose will only be a small λraction oλ the total exposure e.μ., DS reported only % neutron dose at . km λrom the Hiroshima epicenter [ ] . In order to mimic such a mixed λield, a kVp orthovoltaμe X-ray machine is located on site to allow irradiatinμ samples with the necessary additional dose oλ photons. To demonstrate the use oλ this λacility, we present results λrom initial test usinμ the in vitro cytokinesis-block micronucleus assay C”MN, [ ] to measure the induction oλ micronuclei in peripheral human blood lymphocytes exposed to a ranμe oλ neutron doses up to . Gy. The dose-response curves μenerated λor micronuclei λrequency indicated that the R”E oλ this neutron spectrum is between and compared to micronucleus yields induced by kVp X-rays. “s expected, these values λall between those λor accelerator-μenerated enerμetic neutrons [ ] and those λor a reactor-based uranium λission spectrum [ ]. . . Formation of a broad neutron spectrum The key λeature oλ our broad-enerμy neutron irradiator is its use oλ a mixed-μas ion source, with the spectrum dependinμ on the ratio oλ μases in the mixture λed into the ion source. For this work, hydroμen and deuterium were combined at a ratio oλ in one oλ the ion source μas supply cylinders and placed in the accelerator terminal. The ionization process oλ the mixed μas is complicated, as it μenerates many diλλerent ion combinations. To identiλy the actual ion beam ratios and to optimize the beam current, two diλλerent values oλ the μas valve control voltaμe were tested. The selected μas input parameter percentaμe oλ maximum valve voltaμe is used to control the pressure to provide suλλicient beam current. To determine the ratio oλ the diλλerent ion species in our beam, we measured beam current at a ° deλlection, as a λunction oλ the λield strenμth oλ the bendinμ maμnet. Table shows the λractions oλ the various atomic and molecular ions at two extremal pressures we can use outside this pressure ranμe, the beam current is too low or the ion source operation unstable . Several ion species e.μ., D+ and H + cannot be separated maμnetically because their maμnetic riμidity is very close. “s can be seen, increasinμ the valve voltaμe λrom . to . % chanμed the ion ratios sliμhtly λor the molecular, but not atomic ions. “s the major contributions to the spectrum come λrom the H+ and D+ ions, which vary by less than % over this ranμe, we expect the spectrum will not vary siμniλicantly over this ranμe oλ ion source parameters.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

Gas valve control

. %

. %

Ion species D+, H +

.

D +, H D

. %

D+ H

.

%

%

. % . % %

%

%

+

. %

. %

D H+

. %

%

+

H

Table . Ion species percentaμe λor two diλλerent percentaμes oλ maximum μas control voltaμe.

Neutrons are μenerated as the particle beam impinμes on a thick μm beryllium tarμet. “t this thickness, the MeV deuterons and protons are completely stopped in the beryllium. The neutron enerμy spectrum obtained by this conλiμuration was previously [ ] modeled usinμ MCNPX and more recently validated experimentally [ ]. ”rieλly, an EJliquid-λilled scintillation detector and a μas proportional counter λilled with atm oλ hydroμen were used λor measurinμ neutron enerμies above and below . MeV, respectively. The combination oλ the two detection systems covers a wide-enerμy ranμe, λrom . to > MeV. The recoil pulse heiμht spectra acquired by the detector systems were careλully evaluated usinμ diλλerent quasimonoenerμetic neutron beams . – MeV available at the R“R“F accelerator, discriminatinμ the γ-ray siμnals λrom the raw acquisition data with pulse rise time. The two portions oλ the spectrum obtained λrom the two detectors were combined to λorm a kerma-weiμhted total spectrum Figure . Overall, the obtained spectrum is similar to the one evaluated λor Hiroshima [ ], althouμh it is sliμhtly λlatter. “ more detailed discussion oλ the diλλerences between our spectrum and Hiroshima appears elsewhere [ ].

Figure . “ comparison oλ the kerma-weiμhted neutron spectrum μenerated by us hashed with the one at . km λrom Hiroshima μround zero μray .

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. . Irradiation setup Due to the requirement λor a mixed H/D beam, the irradiation λacility was set up usinμ an undeλlected ° anμle beam line in the R“R“F accelerator λacility Figure a . The tarμet assembly, shown in Fiμure b consists oλ a -mm-thick Cu disk onto which a -μm-thick beryllium λoil was diλλusion bonded. The dimensions oλ the copper disk were chosen so that it can be used in lieu oλ a standard . € CF μasket. The tarμet is clamped between two Conλlat λlanμes and doubles as a vacuum window. The tarμet is cooled by water impinμinμ on the copper backinμ plate [ ].

Figure . a Photo oλ the irradiation λacility. ”eam arrives λrom the riμht and impinμes on the beryllium tarμet μenerat‐ inμ neutrons. Samples to be irradiated blood or mice are placed in sample holders shown here empty and mounted on a Ferris wheel rotatinμ around the tarμet coolinμ chamber. “t the leλt is the TE μas ionization chamber used as a beam monitor and the riμht anμle prism used λor aliμninμ the beam line. b Cross-section oλ tarμet and coolinμ cham‐ ber. Direction to the center oλ the sample holders mm away and the monitor chamber mm away are shown.

“s the tarμet coolinμ water lines, supportinμ structures, shieldinμ, and other surroundinμ materials were seen to μive about a % azimuthal variation in dose rate, a vertical Ferris wheel-like λixture Figure a is used to rotate the sample holder tubes λor either blood or mice around the tarμet. Customized tubes mountinμ λrom the rods on the wheel are used to hold the samples with a constant horizontal orientation at a distance oλ mm λrom the tarμet center. The λixture rotates up to samples around the beam axis. The sample holders λor both mice and ex-vivo irradiated blood are based on standard -ml conical centriλuμe tubes ”D, Franklin Lakes, NJ which were modiλied to allow hanμinμ horizontally λrom rods on the wheel, so that the tubes maintain a constant orientation as the wheel rotates. This provides an isotropic irradiation, while maintaininμ the mice in an upriμht orientation, reducinμ stress.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

Durinμ irradiations, the wheel is rotated at a speed oλ about min per revolution and the dose rate adjusted so that the minimal dose is delivered in rotations min with the sample tubes λlipped end-to-end halλ-way throuμh. For pure photon exposure, a kVp Westinμhouse Coronado X-ray machine, placed within m oλ the neutron irradiation λacility, is used. This proximity allows λor λuture mixed-λield studies, where each sample may be immediately transported to the X-ray machine and irradiated aλter neutron exposure, with a time μap between the two irradiations oλ less than min. . . Neutron dosimetry The total dose measurement λor the IND-like neutron/μamma mixed-λield irradiations was perλormed usinμ a custom “muscle TE μas ionization chamber Figure , as described by Rossi et al. [ ]. This chamber is intended λor use in a mixed neutron and γ λield measure‐ ment and λeatures an interchanμeable internal TE plastic sleeve. In the dosimetry measure‐ ments reported here, we used a . -mm-thick sleeve to model the dose deposited at the center oλ the blood samples used. The chamber was λilled with methane TE μas at ~ mm Hμ beλore the dosimetry measurement and sealed. The detector was then attached directly to an elec‐ trometer system and calibrated usinμ a mμ Ra γ-ray source, which had been previously calibrated by the National ”ureau oλ Standards. The dose rate was ~ μGy/h at m λrom the source. “λter calibration, the dosimeter was mounted on the sample wheel λor the IND-like neutron irradiator at ° with respect to the ion beam axis and mm away λrom the tarμet.

Figure . Custom TE μas ionization chamber λor neutron dosimetry shown here with . mm TE plastic sleeve. This λiμure was oriμinally published by Rossi et al. [ ] and has been modiλied and re-published with the permission oλ Radiation Research.

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To extract the dose due to neutrons, γ-ray dosimetry was perλormed separately with a compensated Geiμer–Mueller dosimeter, which is times more sensitive to photons than to monoenerμetic neutrons in the ranμe oλ . – . MeV [ ]. The γ-ray dosimetry was conducted in the same manner as the total dose measurement and then subtracted λrom the latter. Since the γ-ray dose λrom the tarμet rate is essentially isotropic, only inverse-square law corrections were perλormed. The neutron dose rate at the sample position was ~ . × − Gy/h/μ“, representinμ ~ % oλ the total dose rate, with the remaininμ % due to γ-rays. Durinμ the irradiation, the beam current was tuned to and kept at about . μ“, which is equal to a neutron dose rate oλ ~ . Gy/h. ”ecause oλ the possible variation oλ the dose rate relative to the beam current, a second TE μas ionization chamber was added as a monitor at a λixed location downstream oλ the neutron tarμet at an anμle oλ ~ ° relative to the ion beam direction. The monitor ionization chamber was λilled with λlowinμ TE μas, which was reμulated with a constant-density control system. The incident primary particle beam current was recorded with an electrometer coupled to the end oλ the beam line, which is a Faraday cup-like isolated beam pipe with the tarμet at the end. . . Micronucleus assay analysis Micronucleus λormation in peripheral blood lymphocytes is a well-established marker oλ ionizinμ-radiation-induced DN“ damaμe. We have used a recently established cytokinesisblock micronucleus C”MN assay protocol by Fenech [ ] λor accelerated sample processinμ by perλorminμ a miniaturized version oλ the assay in a multi-tube plate system [ ]. Peripheral blood samples were collected λrom three healthy donors aλter inλormed consent IR” protocol #“““F and exposed ml aliquots to nominal neutron doses oλ approxi‐ mately . , . , , and . Gy plus the concomitant . , . , . , and . Gy oλ γ-rays . ”lood sample aliquots were also exposed to , , and Gy oλ kVp X-rays. Two hours post-irradiation, triplicate blood sample aliquots μl λrom each dose point were placed into culture in . ml D-barcoded matrix storaμe tubes Thermo Scientiλic, Waltham, M“ with μl oλ P”-M“X Karyotypinμ medium Liλe Technoloμies, Grand Island, NY . Followinμ h oλ incubation, cytochalasin-” Siμma “ldrich, St Louis, MO was added at a λinal concentration oλ μμ/ml to inhibit cell cytokinesis and the tubes returned to the incubator. “λter a total incubation period oλ h, the cells were harvested. Followinμ hypotonic treatment, the cells were λixed usinμ ice cold λixative methanol–acetic acid . The λixed samples were stored at °C at least overniμht , dropped on slides and stained with Vectashield mountinμ medium containinμ D“PI Vector Laboratories, ”urlinμame, C“ . The slides were imaμed usinμ a Zeiss λluorescent microscope “xioplan Carl Zeiss MicroImaμinμ Inc., Thornwood, NY with a motorized staμe and a × air objective. Quantiλication oλ lymphocyte micronuclei yields were determined by automatic scanninμ and analysis by the MetaλerMN Score soλtware MetaSystems, “lthaussen, Germany . ”etween and , binucleate cells were analyzed λor each data point.

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

Figure a shows the comparison oλ the micronucleus yields λor lymphocytes exposed to diλλerent neutron or X-ray doses. Overall, a dose-dependent increase in micronuclei yields was observed with increasinμ dose with both radiation λields with the yields induced by the X-rays λollowinμ a linear quadratic behavior with dose and the neutron data λollowinμ a linear trend. The neutron data are actually induced by a mixed neutron + photon λield. The dashed line shows that what we would expect λrom a pure neutron irradiation. This estimate was obtained by calculatinμ excess micronucleus yields over controls λrom the photon component % oλ the total dose based on the linear quadratic λit to the X-ray data. This value was then subtracted λrom the mixed-λield yields at the same total dose. The resultant diλλerence corresponds to the micronuclei yields that would be seen in a pure neutron irradiation. . . Relative biological effectiveness RBE calculations The potential bioloμical eλλects and damaμe caused by radiation depend not only on the radiation dose received but also on the type oλ radiation. R”E was introduced to normalize the radiobioloμical eλλects caused by diλλerent types oλ radiation. R”E is deλined as the ratio oλ photon dose in our case kVp X-rays to the dose oλ the radiation λield oλ interest in our case neutrons , providinμ the same bioloμical eλλect [ ]. The bioloμical eλλects caused by neutrons vary with enerμy and produce μreater damaμe than X- or γ-rays. In μeneral, λor the same dose, neutrons are much more eλλective in damaμinμ cells because neutron-induced secondary particles, λor example, low-enerμy protons, have hiμh LET linear enerμy transλer and photon-induced particles are electrons havinμ low-LET. In this paper, we describe experiments aimed at measurinμ the neutron R”E λor micronucleus λormation in peripheral blood lymphocytes as part oλ the irradiator testinμ. Onμoinμ experiments usinμ a variety oλ cytoμenetic, transcriptomic, and metabolomic endpoints, in human blood and in mice, will be published separately. The R”E λor the mixed-λield irradiation neutrons and γ-rays Figure b was calculated λrom the linear and linear-quadratic reμression curves, λitted to the neutron and X-ray data,

Figure . a Micronucleus λrequency in human peripheral blood lymphocytes exposed ex vivo to neutrons or X-rays. The data show mean micronuclei per binucleate cell yields λrom three healthy volunteers. Error bars show ± SEM. The mixed-λield yields plotted vs total dose neutrons + γ-rays . The solid lines indicate a linear neutrons or linear-quad‐ ratic X-rays λit. The dashed line indicates the estimated pure neutron component. b R”E values λor the mixed λield and λor the pure neutrons, calculated λrom panel a see text λor details .

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respectively, by solvinμ λor the X-ray dose that would μive the same micronucleus yield as a μiven dose oλ the mixed neutron/γ-ray λield. The pure neutron R”E will be sliμhtly hiμher than the R”E value oλ the mixed λield. This was evaluated in the same way λrom the dashed line in Figure a. The limitinμ R”E value oλ is hiμher than the value oλ . reported λor MeV monoenerμetic neutrons [ ] but lower than the value oλ calculated λor a reactor λission spectrum [ ], in accordance with what we would expect, based on the neutron enerμies.

. Summary “ mixed beam oλ atomic and molecular deuterons and protons, accelerated to MeV, impinμes on a thick beryllium tarμet, and the resultant neutron spectrum is the sum oλ the spectra λrom the ”e d,n ” reaction hiμher-enerμy neutrons and the ”e p,n ” reaction lower-enerμy neutrons . The neutron enerμy spectrum is manipulated by adjustinμ the ratio oλ protons and deuterons to mimic the neutron spectra λrom an IND exposure λor medical triaμe and bio‐ dosimetry studies. Speciλically, it mimics the Hiroshima μun-type bomb spectrum at a relevant distance λrom the epicenter – . km and is siμniλicantly diλλerent λrom a standard reactor λission spectrum because the bomb spectrum chanμes as the neutrons are transported throuμh air. The neutron spectrum oλ this irradiator was measured and is veriλied comparable with the Hiroshima bomb spectrum at . km. “bout % oλ the radiation dose is delivered by neutrons and He rest by γ-rays. “ comparison oλ the bioloμical eλλect oλ neutron and X-ray exposure on micronuclei yields in peripheral lymphocytes demonstrated that the IND-spectrum irradiator described above μives R”E values within the expected ranμe.

Author details Yanpinμ Xu “ddress all correspondence to yx

@cumc.columbia.edu

Radioloμical Research “ccelerator Facility, Columbia University, Irvinμton, US“

References [ ] Hei TK, ”allas LK, ”renner DJ and Geard CR usinμ a microbeam. J Radiat Res, “ –“ .

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Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

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] Huber R, Schraube H, Nahrstedt U, ”raselmann H and ”auchinμer M Doseresponse relationships oλ micronuclei in human lymphocytes induced by λission neutrons and by low LET radiations. Mutat Res Fundam Mol Mech Mutaμen, , – .

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] Rossi HH, ”ateman JL, ”ond VP, Goodman LJ and Stickley EE The dependence oλ R”E on the enerμy oλ λast neutrons . Physical desiμn and measurement oλ absorbed dose. Radiat Res, , – .

/”C

“ liquid scintilla‐

Cytokinesis-block micronucleus cytome assay. Nat Protoc, ,

–

Radiation and Environmental Biophysics: From Single Cells to Small Animals http://dx.doi.org/10.5772/62623

[

] Lue S, Repin M, Mahnke R and ”renner D Development oλ a hiμh-throuμhput and miniaturized cytokinesis-block micronucleus assay λor use as a bioloμical dosim‐ etry population triaμe tool. Radiat Res. – .

[

] Hall EJ and Giaccia “J, Radiobioloμy λor the radioloμist. th ed. Philadelphia Lippin‐ cott Williams & Wilkins .

                                           

129

Chapter 6

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident Markus Zehringer Additional information is available at the end of the chapter http://dx.doi.org/ 10.5772/62460

Abstract The contamination oλ our environment and oλ λood with artiλicial radionuclides oriμinates λrom several sources. First, nuclear powers spread contamination all over the Northern Hemisphere by carryinμ out more than atmospheric bomb tests λrom to . The peaceλul use oλ nuclear λission brouμht several accidents in nuclear installations [nuclear power plant NPP ]. This beμan in the late s and ended recently with the NPP’s core meltinμs at Fukushima-Daiji in . The catastrophe at the Chernobyl NPP in spread enormous λallout over most parts oλ Europe. ”esides the artiλicial contamination, one has to mention the exposure to naturally occurrinμ radionuclides λrom the uranium and thorium decay series. From on, the State Laboratory ”aselCity beμan a monitorinμ proμramme oλ λood. Special equipment λor the analysis oλ α-, β-, and γ-emittinμ radionuclides had to be built. In / , the laboratory had to manaμe thousands oλ samples accordinμ to the accident at Chernobyl. The Government estimated the dose oλ the mean Swiss population λrom the inμestion oλ contaminated λood to be to mSv. Today, the contamination oλ λood has lowered siμniλicantly. The Oλλice oλ Public Health estimated the total inμested dose oλ about . to . mSv/year. The main contri‐ bution comes λrom potassiumK . mSv/year and λrom natural radionuclides oλ the uranium and thorium decay series. The remaininμ contamination λrom the bomb λallout is less than . mSv/year. Keywords: Chernobyl, dose estimation, λood, radioactive contamination, radiocaesi‐ um, radiostrontium

. Introduction In the s, Otto Huber and his team λrom the University oλ Fribourμ started the reμular monitorinμ oλ radioactivity in Switzerland [ ]. Some years later, the λederal μovernment

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initiated a countrywide monitorinμ proμramme. In , the λirst nuclear power plant NPP oλ ”eznau came on line to produce electric power. Today, λive NPPs are producinμ about % oλ the electric power in Switzerland. In addition to the emission controls oλ the NPPs and other radiation-producinμ λacilities, the monitorinμ oλ radioactive λallout λrom the atmospheric, nuclear bomb tests is oλ special concern. Over bomb tests in the atmosphere led to a contamination oλ the Northern Hemisphere with lonμ-lived radionuclides, such as radiocae‐ sium, radiostrontium, and plutonium. The contamination situation was then aμμravated by the reactor λire oλ the NPP oλ Chernobyl in late “pril oλ . In Switzerland, the southern and eastern parts were more aλλected in southern Switzerland, it rained on – May over mm precipitation . On May, the National Emerμency Operations Centre N“Z started a monitorinμ proμramme λor λood with the help oλ the specialised laboratories in D(bendorλ, Freiburμ, Lausanne, Spiez, W(renlinμen, and the State Laboratory ”asel-City. In October , a symposium on the measurements and their interpretation was held in ”erne [ ]. In , other state laboratories took part in the monitorinμ proμramme. Five years later, when radiation levels were reduced considerably, most oλ the state laboratories reduced their monitorinμ proμrammes aμain many state laboratories even cut oλλ their survey activities. Until , the radioactivity survey was mainly supported by the specialised laboratories. The core meltinμs oλ the Fukushima-Daiji NPPs μave a short increase in the survey activities λor the years / in Switzerland.

. Legislation of the radioactivity controls in Switzerland In Switzerland, the radioactivity survey is a task oλ the Federal Oλλice oλ Public Health ”“G , an oλλice oλ the Federal Department oλ Home “λλairs. One aspect is the monitorinμ oλ λood, which is done in collaboration with the state laboratories oλ the cantons. In , the Federal “ssembly oλ the Swiss Conλederation enλorced the Radiological Protection Act [ ] alonμ with several Ordinances e.μ., the Radiological Protection Ordinance [ ]. The assessment oλ λood is reμulated in the Ordinance on Contaminants and Constituents in Food λrom Table [ ]. This ordinance reμulates the most important μroups oλ radionuclides in a special way. For artiλicial radionuclides, two limits are set. The tolerance values€ should not be exceeded when λood is μrown or produced with μood manuλacturinμ practise. When values are over the tolerance limit, the λood is considered as reduced in its value€. Limit values€ are oλ toxico‐ loμical concern. When they are exceeded, the consumption oλ this λood may lead to a dose oλ more than mSv/year. In emerμency situations, when radioactive contamination may occur, special limit values are λormulated. “λter the accident oλ Chernobyl, such special conditions were λormulated λor imports λrom East European countries [ ]. Each importation oλ wild μrown mushrooms has to be documented by an importation certiλicate, which documents a radiocaesium level below ”q/kμ. In , the Federal Food Saλety and Veterinary Oλλice enλorced precautions λor the importation oλ Japanese λood and λeed oriμin λrom animals. Importations λrom speciλic preλectures have to be accompanied by a certiλicate oλ a radiocaesium analysis oλ the λood [ , ]. The Federal Oλλice oλ Public Health will implement revised ordinances λor Japan and

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Chernobyl in the next λew years. Even, the Government intends to annul most oλ the limit values λor radionuclides in times oλ non-crisis but to implement special limit values λor crises. Radionuclides

Babyfood,

Liquid

Food of main

Food of minor

infant

food

importance

importance

formulas Radiostrontium

/

/

/

/

Sr

+

Radioiodine +

Radiocaesium +

/

/

/

/ ,

/

/

/

/ ,

. /

. /

. /

. /

«/

«/

«/

«/

«/

«/

«/

«/

I

+

Cs

Plutonium and trans-Pu-elements Natural radionuclides Σ

Ra,

Th,

+

+

U

Natural radionuclides Σ +

Pb,

Po,

Th,

Pa

+

Ra,

Tritium

/

Radiocarbon Others

/ /

/

/ ,

« /

/ , /

/ /

, ,

/ ,

Except λor ”razil nuts no limits . Special tolerance and limit values λor μame / ”q/kμ and wild berries / ”q/kμ. Special limit value λor Po in seaλood ”q/kμ. “ll values in ”q/kμ. First value oλ each row tolerance value second value limit value. Second line limits oλ the ordinance λor imports oλ λood λrom or oriμin oλ Japan [ ]. Table . Ordinance on contaminants and constituents in λood radionuclides€ [ ].

. “ppendix No.

List oλ limit values λor

. Radiation in the environment Radioactive sources are in our body and everywhere outside in the environment. They can be divided in two μroups oλ sources naturally occurrinμ radionuclides, which are part oλ naturally occurrinμ radioactive materials NORM , and technoloμically enhanced naturally occurrinμ radioactive materials TENORM . In addition, there are man-made artiλicially produced occurrinμ radioactive materials. Primordial radionuclides are radionuclides with lonμ halλ-lives, even lonμer than the earth’s aμe. They play an important role in the earth’s radioactivity. The three natural decay series oλ

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Uranium U, U and thorium Th belonμ to them. Secondary radioactive elements are built by the decay oλ these primordial radionuclides and belonμ to the inventory oλ our soils. Some dose-relevant radionuclides oλ these decay chains are radium Ra, Ra, and Ra , radon Rn and Rn , lead Pb , polonium Po , and thorium Th, Th, and Th . “nother ubiquitous radionuclide is potassiumK , Which is a larμe part to the annual received dose. Cosmoμenically produced radionuclides are, λor example, beryllium- ”e , tritium H , or radiocarbon C [ , ]. “rtiλicial radionuclides have been produced and released to the environment since the s, when nuclear weapons development and tests beμan in the United States. These tests oλ nuclear λission in the United States, USSR, China, G”, and France led to λallout with a μreat number oλ radioactive λission products and activated radionuclides. Over atmospheric bomb tests λrom to led to a contamination oλ the Northern Hemisphere with artiλicial radionu‐ clides such as C, H, radiocaesium Cs and Cs , radiostrontium Sr , and plutonium Pu . [ ]. It is because oλ scientists, such as Ernest Sternμlass, who investiμated and proved the neμative eλλects oλ the bomb λallout on childhood mortality. Their warninμs helped to enact the partial test ban treaty, which most nuclear powers ratiλied [ ]. “λter , the λallout clearly decreased. One can clearly see this in sediment proλiles oλ lakes e.μ., lake sediment investiμations in Switzerland [ ]. NPPs are also emitters oλ artiλicial radionuclides. Several accidents caused the release oλ larμe quantities oλ radioactive λallout to the environment. “ccidents were the burn oλ one pile at the Windscale reactor in Sellaλield in , the partial core meltinμ oλ the Three Mile Island reactor in Harrisburμ in , the nuclear catastrophe oλ the Chernobyl NPP in , and the core meltinμs oλ the NPPs oλ Fukushima-Daiji in Japan . The catastrophe oλ Chernobyl aλλected many European countries, many thousands oλ miles away λrom the NPP μround. The use oλ radionuclides in diaμnoses and therapies aμainst cancer leads to the release oλ shortlived radionuclides, such as iodine I , technetium mTc , indium In , lutetium Lu , yttrium Y , and others. They do not enter the λood chain because oλ their short halλ-lives and are thereλore oλ minor concern.

. Radiation detection The λollowinμ overview oλ radioactivity laboratory equipment λor λood control is only a brieλ summary oλ the required equipment. For inλormation about the theory oλ radiation detection and measurements, technical details, or special applications, we reλer to the standard literature [ – ]. . Dose rate monitors Measurement devices to count the dose rate oλ radioactive sources are not sensitive enouμh λor the precise contamination measurements oλ λood. However, they can be adequate λor Treaty banninμ oλ nuclear weapon tests in the atmosphere, in outer space, and under water.

“uμust

.

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident http://dx.doi.org/ 10.5772/62460

screeninμ analysis. In and , the State Laboratory Ticino and the Federal Oλλice oλ Public Health used dose rate monitors to screen wild boars shot in the southern parts oλ Switzerland. They only sampled animals over a certain dose rate λor precise γ-spectrometric analysis λor radiocaesium [ ]. This kind oλ measurement equipment is not sensitive enouμh to detect contamination in the case oλ λood imports λrom Ukraine, Japan, and other contami‐ nated countries. Thereλore, one cannot save the countinμ on a γ-spectrometer. . . γ-Spectrometry It is oλ primary importance to be equipped with a γ-ray detector. γ-Spectrometry can be operated with inorμanic scintillators, such as pure crystals oλ sodium iodide NaI and caesium iodide CsI or doped crystals, such as NaI Tl or CsI Tl . NaI Tl is the most used scintillator and has excellent liμht yield and a μood linear response, but enerμy resolution is quite limited. Today, the best choice is semiconductor detectors. Crystals oλ silicon, μermanium Ge , cadmium-telluride, and others are the detector materials. Ge detectors have been widespread since , when the production oλ hiμh-purity Ge monocrystals became possible. They have to be kept under vacuum and cooled with liquid nitroμen. The detectors have an excellent enerμy resolution. Thereλore, even complex spectra can be analysed without prior chemical separation steps. Two criteria are oλ importance resolution and sensitivity. Enerμy resolution oλ Ge detectors is excellent . to . keV at . MeV, below keV, less than keV FWHM λull width at halλ maximum . The eλλiciency oλ the detector relative eλλiciency compared to a NaI detector at . MeV and the relation oλ the peak to Compton backμround are the most important λactors λor the sensitivity. Today, Ge detectors with eλλiciencies oλ % and hiμher are available. The peak/Compton quotient is more than . In our laboratory, we use Ge detectors with % eλλiciency. Important λactors λor quantitative γ-spectrometry are the shieldinμ oλ the detector and the eλλicient suppression oλ the electronic noise oλ the ampliλier system. γ-Spectrometry has the advantaμe that γ-radiation can be measured without the elimination oλ the matrix. Thereλore, sample preparation takes only a short time. γ-Spectrom‐ eters need an exact calibration over the whole enerμy ranμe e.μ., – keV . Calibrations with certiλied radioactive sources are necessary λor every countinμ μeometry used volume and shape oλ the sample, and distance λrom the detector Calibration solutions consist oλ a mix oλ short-lived radionuclide with emission lines over the whole enerμy ranμe e.μ., Cd, Co, Sn, Cs, Y, and Co . “λter year, the short-lived radionuclides are partly disinteμrated thereλore, the calibration mix cannot be used anymore. This can be overcome usinμ mixtures oλ Eu halλ-liλe oλ . years in combination with a low-enerμy γ-nuclide, such as Pb or “m. When usinμ Eu, summation eλλects have to be corrected properly. There are other important λactors to consider besides the countinμ μeometry. The sample matrix itselλ absorbs γ-rays beλore they arrive at the detector. These selλ-absorption eλλects are a λunction oλ the sample μeometry and the elemental composition and the density oλ the sample matrix. Normally, calibrations and eλλiciency curves are produced with calibration standards in water or μels oλ density . Density corrections can be calculated λor every material and μeometry with means oλ a soλtware based on Monte Carlo simulations. The backμround radiation has to be considered. Some backμround radiation remains, even with μood shieldinμ

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Radiation Effects in Materials

with lead and copper. This backμround consists oλ radionuclides oλ the natural decay series, such as Pb and ”i and others. For every countinμ μeometry, the backμround has to be measured with water-λilled containers oλ the needed countinμ μeometries. The γ-spectra have to be subtracted by the speciλic backμround spectrum. Radionuclides with cascade emissions show coincidence summinμ eλλects e.μ., Cs and Eu . Spectra have to be corrected or the measurement must be repeated with a distance between sample and detector. For short-lived radionuclides, their partial decay has to be corrected to the reλerence date e.μ., the date oλ the samplinμ . Further advice and descriptions over quantitative γ-spectrometry are μiven in the literature [ ]. . . -Spectrometry For the countinμ oλ β-rays, the sample matrix has to be eliminated. “n exception is water samples e.μ., the measurement oλ H needs not much sample preparation, only the mix oλ the water sample with a scintillator cocktail . Some important β-nuclides, such as H, C, Sr, Sr, and Y, can be analysed with scintillation countinμ. Commercially available scintillation counters can detect α- and β-decays. This widens the spectrum oλ radionuclides e.μ., Rn can be analysed in water samples or in charcoal air samples . When samples are analysed directly, the sensitivity is μiven by the small sample amount oλ typically some millilitres. Radiostrontium, Sr and Sr, are important λission products. One possibility is to extract the Sr with the use oλ speciλic crown ethers λrom the sample. In our laboratory, we have developed a λast analysis scheme λor water samples [ ]. “nother possibility is to clean up extracts over a column λilled with crown ethers. These methods are suitable λor activity concentrations hiμher than ”q/kμ. For sensitive analyses, the β-spectrometers oλ choice are μas λlow proportional counters. We use this technique λor the analyses oλ Sr traces in λood, human, and environmental samples. The method is based on the countinμ oλ the dauμhter nuclide, Y. ”eλore the countinμ starts, a riμorous elimination oλ the matrix and disturbinμ β-nuclides, such as K, is necessary. With an oxalate precipitation step, most oλ the K is eliminated. Then, Y is separated λrom Sr by precipitation as hydroxide. The Y OH is dissolved and precipi‐ tated as Y oxalate . These β-sources are pure enouμh λor countinμ. Countinμ is perλormed in consecutive runs, as Y decays durinμ the countinμ halλ-liλe is h . “ μood-quality criterion λor the purity is the measured decay oλ the source. Decay should be near h. When decay is slower, impurities are present. The conserved Sr solution may be prepared and analysed aμain aλter days the built-up Y will then arrive equilibrium with Sr . Quite sensitive analyses may be perλormed down to m”q/kμ. Countinμ time is days. Thereλore, several detectors should be available. Our Canberra α/β-counter L” can take up to λour drawers with λour sample holders each [ ]. . . -Spectrometry Like β-spectrometry, α-spectrometry requires an elimination oλ the sample matrix. Only water samples need a minimal preparation. Two countinμ techniques are common today scintilla‐ tion countinμ and passivated implanted planar silicon PIPS detectors. We use liquid scintil‐ lation counters in our laboratory λor the analyses oλ uranium, thorium, radium, and polonium.

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident http://dx.doi.org/ 10.5772/62460

“ccordinμ to the methods published by W. Jack McDowell, the water sample is extracted once with some millilitres oλ a nuclide selective extractant, which contains the scintillator cocktail λor the α-analysis. Very low activity concentrations – m”q/L can be achieved [ ]. The disadvantaμe is the poor enerμy resolution. “lso, α/β-discrimination has to be set careλully. “nalysis time is hours λor water samples containinμ m”q. “nalyses with PIPS detectors show μood enerμy resolution and eλλiciencies λrom % to %. Countinμ has to be perλormed under vacuum and very thin layer α-sources are needed. The sample matrix has to be destroyed by ashinμ, etc. λollowinμ a clean-up speciλic nuclide extraction, scavenμinμ, etc. and a preparation oλ a thin-layer source by means oλ electroplat‐ inμ or coprecipitation. Many actinides, such as uranium, thorium, and plutonium, may be analysed well described in [ ] . Some elements such as Po and radium nuclides may be auto-deposited onto special surλaces. Po is auto-deposited under reductive conditions onto silver or copper disks aλter a microwave diμestion oλ the sample [ , ]. Radium nuclides Ra and Ra are auto-deposited onto MnO surλaces at pH as has been shown by Surbeck [ , ]. These methods are suitable λor drinkinμ water and mineral water analyses. Some new developments were done λor uranium and thorium analyses in honey and spices [ , ] Figure .

Figure . Equipment of a radioactivity laboratory: “ γ-spectrometry ” α-liquid scintillation PER“LS C α-Spec‐ trometry PIPS detectors and D β-spectrometry μas proportional counter , drawer with Y oxalate sources.

. . Neutron activation analysis NAA IN““ instrumental neutron activation analysis is based on the production oλ radionuclides by nuclear reactions. Thermal neutrons can activate many elements. The eλλiciency oλ this irradiation process depends on the λlux density oλ the neutrons and the cross-section oλ the nuclear reaction. The thermal neutrons are μenerated in a nuclear reactor, λor example, at the University oλ ”asel “GN-P, a liμht water moderated swimminμ pool reactor .

137

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Radiation Effects in Materials

The samples – μ material are inserted into the core over a cannula throuμh the so-called μlory hole and irradiated λor min with a power rate oλ kW. “λter a coolinμ time oλ some hours, the samples are counted on an HPGe detector. We used IN““ λor the analysis oλ total bromine content. ”romide is built by the decay oλ the λumiμant methyl bromide. We used this technique λor many years to determine the total bromine in spices, tea, and dried mushrooms. “nother application is the determination oλ the total bromine content as a screeninμ analysis λor λlame-retardants in plastic materials [ ]. U and Th can be determined by IN““ in suspended matter and sediments [ ]. In addition, total iodine content in iodine rich λood, such as alμae, can be determined over the activation oλ I to I, which decays to Xe [ ]. We mentioned the use oλ IN““ as a completion oλ the possibilities oλ γ-spectrometry. These applications will not be discussed λurther, because the analytes are not radionuclides.

. Results from

years of food control

In ”asel, the Government decided to buy the equipment λor the monitorinμ oλ β- and γ-nuclides in because oλ the NPP accident at Harrisburμ in . Thereλore, we were the only state laboratory that was prepared when the accident at Chernobyl happened. In and , thousands oλ samples were analysed. The λallout λrom bomb tests and the NPP accident oλ Chernobyl resulted in the ubiquitous contamination oλ the landscapes oλ the Northern Hemisphere. The core meltinμs at the NPP oλ Fukushima-Daiji also reached Europe, but the λallout was considerably lower than λrom Chernobyl. The situation aλter the Chernobyl λallout in Switzerland is well described in some papers [ – , ]. The contamination oλ λarmland leads to contaminated λood, such as milk or veμetables. These matrices are an important part oλ the Swiss survey proμramme. The λallout λrom Chernobyl aλλected the reμions oλ southern Switzerland the most total rain oλ mm . This has to be compared to the washout in eastern Switzerland with mm and the reμions oλ ”asel and Jura with mm rain. . . Milk and milk products In , the State Laboratory ”asel-City started the λirst reμular radioanalyses in ”asel. Milk samples λrom local milk production centres in northwest Switzerland oλ the states cantons oλ “arμau, ”asel-Campaiμn, ”asel-City, Solothurn, and Jura were analysed with β- and γspectrometry. On May , aλter the accident in Chernobyl, the λrequency oλ the survey was intensiλied. On and May, radioiodine activity concentrations between and ”q/L I were measured. The milk λrom the mountainous reμion oλ the state oλ Jura showed lower values than in the states localised in the plain ”q/L I May . In the milk distribution centres oλ ”asel-City, the milk λrom the diλλerent reμions had to be mixed in such a way that the population received milk with activities below ”q/L. Due to its short halλ-liλe, the

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident http://dx.doi.org/ 10.5772/62460

activity oλ radioiodine λell under the detection limit . ”q/L in July. The activities oλ caesium and strontium were quite lower but resisted lonμer. The activity line oλ total caesium in the milk oλ the state oλ Jura Figure shows a maximum value oλ ”q/L. In the λollowinμ years, smaller peak values could be observed due to the λact that the cows were λed with contaminated hay λrom the year beλore. “λter , the total caesium level λell below ”q/L, except λor some λarms in southern Switzerland, where, even in , the radiocaesium level oλ the milk oλ one λarm was over the tolerance limit oλ ”q/kμ.

Figure . Results of the monitoring of milk from northwest Switzerland. Notice the sharp peaks due to the Chernob‐ yl λallout. The Sr activity concentration shows a steady decline λrom to .

We λound much lower activity oλ Sr with a maximum value oλ . ”q/L on March in Jura. In the Swiss “lps, the level reached ”q/L. “λter , the contamination oλ the milk λrom the canton oλ Jura reached a value oλ approximately . ”q/L. The present contamination oλ Swiss milk is hiμhest in the “lpine reμions oλ the states oλ Grison and Ticino, where the radiostrontium level is a λactor hiμher than in the rest oλ Switzerland . – . ”q/L , and radiocaesium reaches ”q/L λor the hiμhest value . – ”q/L [ , ].

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Many milk products were analysed in Swiss cheese, milk powder, butter, yoμurt, and cream [ , ]. These investiμations showed the same trends in somewhat lower activity concentrations. Two drinks also showed hiμher levels oλ radiocaesium – ”q/L in , as they contained milk serum. The same contaminated milk λrom was used to produce milk powder. This milk powder was used λor the production oλ chocolates. Milk chocolate contains to μ milk powder – mL milk per μ chocolate. We analysed the λirst samples in autumn λor a local chocolate producer. Soon, we noticed hiμher levels when chocolates contained hazelnuts. These chocolate samples were in the ranμe oλ ± ”q/kμ radiocaesium. In contrast, chocolates without nut inμredients showed lower activities ± ”q/kμ . These investiμations showed that the contamination level oλ chocolates is even more λrom the use oλ hazelnuts % than λrom the milk ~ % . In the λollowinμ year, we λound even hiμher radiocaesium values ”q/kμ in chocolates without hazelnuts and . k”q/kμ in chocolates with hazelnuts. Even chocolates without hazelnuts showed hiμher values. We explained this with hiμher values in milk. Hence, we started a special survey proμramme λor hazelnuts. . . Wild-grown vegetables 5.2. . Hazelnuts and other nuts

Figure . Activity concentrations of radiocaesium in hazelnuts. Plots to the leλt Comparison oλ the radiocaesium lev‐ el in chocolates with and without hazelnuts . Plot to the riμht Development oλ the activity in hazelnuts λrom ”asel.

The investiμation oλ chocolates containinμ hazelnuts showed that the latter were part oλ the contamination. In and , more than hazelnut samples λrom a chocolate producer oλ the reμion were analysed λor radiocontaminants. In , the contamination level reached a total radiocaesium activity oλ up to k”q/kμ. Most hazelnuts were imported λrom Turkey, a country that was seriously contaminated with λallout λrom Chernobyl. Since , we also investiμated diλλerent nuts λrom other countries. Hazelnuts λrom Turkey remained the only contaminated nut species. Even in , years aλter the catastrophe oλ Chernobyl, one hazelnut sample had to be rejected. It did not reach the limit value but was over the tolerance

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident http://dx.doi.org/ 10.5772/62460

value oλ ”q/kμ. “λter , the contamination oλ hazelnuts in Switzerland and abroad remains under ”q/kμ meanwhile, in Turkey, the contamination level was reduced much more slowly due to the hiμher contaminated soils Figure . 5.2.2. Brazil nuts ”razil nuts Bertholletia excelsa are known to accumulate earth alkaline metals λrom soil. First, this was shown with barium. Then, Penna-Franca detected the radium nuclides Ra and Ra, both λrom the natural decay series oλ uranium and thorium, in amounts oλ ”q/kμ. In Switzerland, imported ”razil nuts showed to ”q/kμ total radium. This means -λold oλ the radium content oλ the total diet in Europe. The consummation oλ ”razil nuts is estimated to be . μ/day and person. Thereλore, the consummation oλ ”razil nuts is not relevant. In literature, it is advised to consume ”razil nuts to enhance the selenium level. Two ”razil nuts lead to a yearly dose oλ μSv, which is relevant [ ]. “nother important alkaline earth metal is strontium. Its most important radioactive nuclide is Sr. Froidevaux et al. [ ] measured to ”q/kμ in imported ”razil nuts. “s ”razil nuts are oλten part oλ nut mixtures, the measured natural radioactivity is mainly produced by the ”razil nuts contained in the mixture. 5.2. . Mushrooms Mushrooms are known to be orμanisms that can accumulate heavy metals λrom soil. Thereλore, mushrooms λrom abroad and λrom Switzerland were oλ concern in . More than samples were analysed in our laboratory λor radiocaesium. samples had to be rejected. They showed a contamination level oλ more than ”q/kμ. The ranμe oλ all analysed mushrooms was λrom to more than ”q/kμ. Swiss mushrooms and mushrooms λrom abroad then did not show any siμniλicant diλλerence in their contamination level [ ]. From on, mushrooms were reμularly analysed, but violations became rare. “ quite diλλerent situation could be observed in South ”avaria, Germany. “t the end oλ “pril , much Chernobyl λallout was washed out in southern ”avaria over several days. In Munich, the local dose rate increased up to . μSv/h -λold over the normal value . Thereλore, the contamination level in wild-μrown mushrooms and berries reached hiμh values λive-λold the normal radiocaesium activities due to the bomb λallout . Mushrooms with mycorrhiza, such as boletus species Hydnum repandum and Boletus badius , blueberries, mosses, and lichens, were most aλλected [ – ]. Other mushrooms, such as porcini, champiμnons, and chanterelles, did not show this eλλect. In , bay boletes B. badius showed radiocaesium levels oλ to , ”q/kμ and porcini λrom to , ”q/kμ. In , activities were reduced remarkably in boletes to ”q/kμ and porcini to ”q/kμ [ ]. Similar values were reported in “ustria [ ] and Switzerland [ ]. Even in , bay boletes were λound with maximum activities oλ more than ”q/kμ, whereas porcini showed a reduced contamination level with a maximum oλ ”q/kμ. The reduction was slow compared to West European countries. For example, in Spain, values ranμed λrom to ”q/kμ λor radiocaesium and λrom . to

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. ”q/kμ λor radiostrontium. Mushrooms oλ a special reμion in the canton oλ “arμau Swit‐ zerland show a continuous λall oλ the activity λrom to [ ]. Wood soils build their own biosphere dead leaves, pins, etc., build the humic λraction oλ the soil. The plants take up the radioactivity λrom the soil. The radioactivity is recycled to the soil throuμh the λall oλ the leaves and pins. 5.2. . Wild-grown berries In , the State Laboratory ”asel-City analysed approximately berry samples λrom Switzerland. Strawberries showed a quite low activity . ”q/kμ radiocaesium , whereas currants, raspberries, elderberries, and μooseberries showed siμniλicantly hiμher activities ± ”q/kμ . The reason is that strawberries are cultivated in μreenhouses, in the shelter. Only in was our λocus set on blueberries and other wild-μrown berries. These products are imported in biμ charμes oλ tons λrom East European countries, such as Ukraine, Poland, Russia or Hunμary. From analysed samples, we reμistered eiμht violations because oλ too hiμh activities oλ radiostrontium. In the λollowinμ years, we analysed more than samples with λurther violations λor products λrom “ustria, Ukraine, or Poland. The products were blueberries and blueberry products, such as marmalades. Violations were mostly because oλ radiostrontium > ”q/kμ and radiocaesium > ”q/kμ [ ]. Wild berries μrow in woods. The soil is more acid and promotes the uptake oλ the contaminants. ”ecause oλ the cycle soilplant-soil, the residues in the plants are reduced only slowly compared to berries μrown on λarmland. . . Vegetables and fruit 5. . . Vegetables Leaλy veμetables were, besides milk, the most contaminated λood. Depositions λrom washouts on spinach and salad cultures happened just beλore harvest. Radioiodine level reached almost ”q/kμ in spinach. Thereλore, it was advised that small children, preμnant women, and nursinμ women should not consume this kind oλ λood. The investiμation oλ mother’s milk showed considerable amounts oλ radioiodine up to ”q/L . We tried to reduce the contam‐ ination on salads with washinμs but with only poor success. In May , leaλy veμetables were most aλλected by radioiodine I and I radioiodine was % oλ the measured total dose. Radiocaesium Cs and Cs was % and other short-lived radionuclides, such as Ru, ”a, La, and Mo, μave approximately % to the total dose. We noticed many violations oλ the limit values λor radioiodine and radiocaesium and violations λor baby λood λrom a total oλ samples analysed . This survey λocused on λood with hiμher radiation levels as a screeninμ beλore the γ-analyses were done. The investiμation oλ deep-λrozen veμetables did not show any elevated radiation. These products were produced beλore [ ]. “λter , we started up aμain with controls oλ leaλy and root veμetables. The contami‐ nation level was low and caused by the λallout λrom the bombs. Radiocaesium is normally below the detection limit oλ . ”q/kμ. Radiostrontium is detectable in small amounts oλ . to . ”q/kμ [ ].

Radioactivity in Food: Experiences of the Food Control Authority of Basel-City since the Chernobyl Accident http://dx.doi.org/ 10.5772/62460

5. .2. Herbs Herbs oλ / showed the hiμhest contamination with radiocaesium oλ all investiμated λood. In , oλ herbs contained up to . ”q/kμ. In the λollowinμ year, the contami‐ nation level was even hiμher . ± . ”q/kμ [ ]. 5. . . Fruit In , λruit was less contaminated than veμetables. When harvestinμ time arrived, the radioiodine had already disinteμrated. The radiocaesium level was below ”q/kμ. In , no more contamination was λound < ”q/kμ radiocaesium in dried λruit [ ]. 5. . . Chestnuts Chestnuts, the λruits λrom the chestnut tree, Castanea sativa, are cultivated in northern Italy and southern Switzerland. “t harvest time, in autumn, they are roasted and eaten or processed to crèmes or purees. These were also the reμions with hiμh λallout and washout λrom Chernobyl. The soils and veμetation had elevated activities oλ radiocaesium. “s a consequence, chestnuts contained elevated radiocaesium levels. In , a level oλ ”q/kμ was reached. In the λollowinμ years, the contamination was reduced but only slowly. Even in , one sample violated the tolerance value oλ ”q/kμ. In and , we aμain investiμated chestnuts and chestnut products. The radiocaesium level was reduced by a λactor oλ . The resultinμ level was approximately to ”q/kμ. No more violations were noticed [ ]. . . Flour, bread, and biscuits One year aλter Chernobyl, corn, μrains, bread, shortbreads, and pasta were seriously conta‐ minated with radiocaesium. In , cereals λrom were taken into production. Seven oλ breads and shortbreads and one pasta were over the limit value oλ ”q/kμ and had to be withdrawn. Twenty-one more samples were over the tolerance level oλ ”q/kμ. “s a consequence, the control oλ λlour and λlour products was intensiλied over the next years. However, with the exception oλ one sample in , no more violations oλ the tolerance value were noticed. In , the radiation level λell down to approximately . ”q/kμ radiocaesium in cereals. Natural radionuclides are present in cereals radium – ”q/kμ and thorium . – ”q/kμ . The levels oλ radium are near the limit value oλ ”q/kμ. . . Meat Our own γ-analyses oλ meat in showed values in two cateμories λor cows and calves, the level was low ± ”q/kμ , whereas meat λrom sheep and lamb was quite hiμher contami‐ nated ± ”q/kμ radiocaesium . In the λollowinμ year, the radiocaesium levels were elevated to the same level sheep and lamb ± ”q/kμ and cow and calλ ± ”q/kμ. Durinμ , the Federal Food Saλety and Veterinary Oλλice λormer Federal Oλλice λor Veterinary “λλairs analysed more than meat samples oλ sheep, μoat, cow, piμ, and μame

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mainly λrom eastern and southern Switzerland. The contamination levels in the meat were hiμher in reμions with hiμher depositions oλ λallout. In southern Switzerland, the radiocaesium activity concentrations varied λrom to ”q/kμ. The hiμhest value was λound in a μoat. In contrast to this, in eastern Switzerland, values were λrom to ”q/kμ. In the other parts oλ Switzerland, even lower values were λound. “lmost samples λrom imported meat were analysed. Here, samples had to be rejected due to values more than ”q/kμ. Durinμ the year , a reduction oλ the contamination level was observed, with the exception oλ southern Switzerland cantons oλ Ticino and Grison . The bioloμical halλ-liλe λor radiocaesium was calculated to be approximately days λor sheep and μoat and approximately days λor μame. Piμs showed a halλ-liλe oλ days [ ]. . . Game Game became oλ interest when hiμh radioactive contaminations oλ reindeer were reported in Norway and Sweden. The northern European countries were more hiμhly contaminated with radioactive λallout λrom Chernobyl than other European countries. Wild berries, mushrooms, and lichens are the main λood oλ reindeers. These were seriously contaminated with this λallout. Thousands oλ animals had to be burnt because oλ a violation oλ radiocaesium values that were too hiμh. The survey oλ μame in Switzerland beμan in autumn . We analysed meat λrom λive roe deer and deer with γ-ray spectrometry. The activities were not hiμh. Nevertheless, in , the contamination oλ the μame meat showed hiμher values up to k”q/kμ radiocaesium. From on, μame was investiμated yearly. In , λour objections had to be executed accordinμ to our measurements. It seemed that chamois were the most contaminated μame in Switzerland. “λter , the monitorinμ proμramme was reduced. The detected radioactivity was under the tolerance limit oλ ”q/kμ. Wild boars are an exception. The southern parts oλ Switzerland, such as in ”avaria Germany , are more contaminated landscapes. Here, the contamination oλ wild boar remains a problem up to today. Wild boars search λor their λood on the μround. Elaphomyces, a truλλle species, μrow underμround and are able to enrich radiocaesium λrom soil. It is estimated that these λunμi can be up to % to % oλ the λood oλ wild boars. In , in southern ”avaria and the ”avarian Wood, the contamination levels were up to . k”q/kμ wild boar and up to ”q/kμ in roe deer [ ]. In Switzerland, the State oλ Ticino, in collaboration with the Federal Oλλice oλ Public Health, investiμated wild boars in and . In , wild boars oλ a total oλ animals violated the limit value oλ ”q/kμ. In , they λound such contaminated animals. These animals had to be conλiscated [ ]. In contrast, in the State oλ Zurich, the State Laboratory Zurich λound no violations when they analysed wild boars. The mean activity was low with ”q/kμ radiocaesium [ ]. In , the Umweltinstitut M(nchen reported λrom their monitorinμ proμrammes λor wild-μrown veμetables and μame. More than samples showed contamination levels over the limit value oλ ”q/kμ, and samples showed radiocaesium activities oλ more than , ”q/kμ. Ten samples contained more than , ”q/kμ. The maximum value was , ”q/kμ [ ]. Thereλore, the serious contamination rests a problem in ”avaria.

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Wild boars have to be surveyed over the cominμ years. Fortunately, they are not a widely consumed μame. More important are deer and roe deer, which show considerably lower contaminations [ , ]. . . Seafood and fish 5.7. . Fish In Switzerland, we analysed λish λrom the Rhine River at ”asel λor radioactive contamination in . Fiλteen species cauμht by local λishermen contained to ”q/kμ radiocaesium. These activities were not alarminμ, as λish are not an important part oλ the daily λood con‐ sumption in Switzerland. “μain, the most aλλected reμion was the southern part oλ Switzerland. The mean activity oλ λish species cauμht in the lake oλ Luμano was . ± . k”q/kμ radio‐ caesium with a maximum value oλ more than . k”q/kμ, approximately λive times hiμher than in λish λrom other lakes oλ Switzerland. This lake has no major conλluences and eλλluents such as the lake oλ Maμμiore where the contamination level oλ λish was quite lower [ , ]. “λter , the contamination with radiocaesium λrom the Chernobyl λallout was reduced and reached a level oλ approximately . ”q/kμ λor Cs [ ]. The accidents at the Fukushima-Daiji NPPs μave us cause to investiμate λish importation λrom the Paciλic Ocean. “pproximately % oλ the released λallout reached the sea – P”q Cs . Radiocaesium levels in λish reached k”q/kμ. In , the Japanese Government banned λishinμ in the coastal waters near Fukushima NPP and the λishinμ oλ λish species in some preλectures, which are severely contaminated. Local, private associations oλ λishermen voluntarily imposed a limit value λor radiocaesium oλ ”q/kμ [ ]. “lso in territorial waters, such as lakes, ponds, and rivers, λish accumulated radioactivity λrom λallout. Here, radioac‐ tivity levels reached approximately k”q/kμ λish. In , an intensiλied monitorinμ pro‐ μramme oλ Paciλic blue tunas oλλ the Caliλornian coast showed a sliμht contamination oλ the λish . ± . ”q/kμ Cs and . ± . ”q/kμ Cs . The presence oλ the short-lived Cs proves the contamination λrom the Fukushima λallout [ – ]. “ received dose oλ mSv/year was estimated λrom the consumption oλ kμ λish cauμht within a zone km away λrom the Fukushima NPP. Our own investiμations oλ imported λish λrom the Paciλic show a relatively low contamination level below ”q/kμ radiocaesium, with a mean value oλ approximately . ”q/kμ. Some λish samples also contained the short-lived caesium-nuclide Cs [ ]. Only % oλ the total dose oλ the consumption oλ λish and sea λood oriμinates λrom artiλicial radionuclides, and % is λrom natural radionuclides, such as polonium Po . 5.7.2. Natural radionuclides Natural radionuclides cause the main radiocontamination oλ λish and seaλood. Mussels and molluscs are known to enrich Po in the intestinal tract, whereas the mother nuclide leadPb is not enriched. Cherry and Shannon [ ] published an excellent review. ”oth radionu‐ clides are part oλ the natural decay series oλ uranium and are built at the end oλ the decay chain. Po is a powerλul α-emitter with an enerμy oλ , keV and a halλ-liλe oλ days. Pb is a

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β-emitter with a halλ-liλe oλ years and acts as a reservoir λor Po. “ctivity concentrations ranμe λrom to ”q/kμ. In λish, the Po level is much lower – ”q/kμ [ ]. Our own investiμations on imported seaλood in resulted in objections in mussels and objections in sardines concerninμ too hiμh levels oλ Po. For λood producers and λood distribution aμents, this was surprisinμ. Po was never seen as a problem. One consumes sardines as a whole λish, the intestinal tract included [ , ]. This explains the hiμher con‐ tamination level oλ sardines and anchovies. “ second survey in showed values equal to those in . Since , the limit value λor Po in λish was raised λrom to ”q/kμ the rate oλ λish and seaλood consumed in Switzerland is oλ minor relevance . Thereλore, since , no more objections had to be raised [ ]. “ survey oλ the Pb and Po contamination oλ seaλood in France over the last years reports the same contamination levels [ ]. Even hiμher Po levels were λound in anchovy λrom local λishers at the Turkish coast oλ the “eμean Sea. The annual dose by inμestion was calculated to be μSv [ ]. Low activity concentrations were λound in λish cauμht in Swiss lakes. “ mean value oλ samples was . ± . m”q/kμ Po. Such low values are not astonishinμ. Only the edible parts oλ the λish, without the intestinal tract and entrails, were analysed. Measurements oλ entrails oλ λish samples showed a mean activity concentration oλ ”q/kμ [ ]. . . Baby food ”aby λood is inλant λollow-on λormula that is industrially produced λrom cow’s milk or soybeans. It is μiven to children up to months aλter birth. For this kind oλ λood, more restricted limit values are reμulated concerninμ radionuclides. The μiven limit values are calculated to the λinal reconstructed constitution oλ the λood table . Radioactive contaminants are introduced throuμh the milk into the products. Thereλore, radiostrontium and radium are oλ special interest. In , an investiμation oλ samples oλ λollow-on λormulas showed a severe contamination with radiocaesium. Four samples exceeded the limit value oλ ”q/kμ the hiμhest value was more than . ”q/kμ. Ten λurther samples contained radiocaesium in amounts μreater than today’s tolerance limit oλ ”q/kμ. However, no radiostrontium was analysed, so it is unknown how more violations were present concerninμ too hiμh activities oλ Sr. In and , we analysed baby λood λor both radionuclides. Whereas radiocaesium levels were quite low < . up to . ”q/kμ , the radiostrontium contamination reached almost the same values . ”q/kμ . Radium belonμs to the same element μroup oλ the earth alkaline metals as calcium and strontium. Thereλore, it is not surprisinμ to λind contaminations with radium Ra and Ra in inλant λormulas . – . ”q/kμ [ , ]. . . Spices and salt In / , spices were oλ no special concern. They λiμure as a λood oλ minor relevance, because the consumption rate oλ spices is relatively low in Switzerland. “ second reason is the λact that spices are imported λrom the Middle and Far East, where they were not at all aλλected by the λallout λrom Chernobyl. Over the last years, the radiocaesium content in spices was

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stable to ”q/kμ λor samples analysed. Hiμher activity concentrations were λound λor natural radionuclides λrom the uranium and thorium decay series. For example, white and black pepper and cinnamon contain considerable amounts oλ thorium and radium up to ”q/ kμ . This is near the Swiss limit value oλ ”q/kμ [ ]. Salts belonμ to the spices. Either they are produced λrom evaporation oλ seawater or are yielded λrom mines or salt λields. “ survey oλ products μave the λollowinμ results artiλicial radio‐ nuclides, such as radiocaesium, are not present. “ major contaminant oλ salts is potassium chloride. Thereλore, it is not surprisinμ that K activity concentrations are relatively hiμh in salts ± ”q/kμ. One salt λrom Persia contained k”q/kμ K. Some radionuclides λrom the decay series, such as radium, are present in small amounts . ± . ”q/kμ + Ra [ ]. .

. Honey

In , Swiss honey samples were investiμated with γ-spectrometry. They contained I with a mean oλ . ”q/kμ samples and radiocaesium with ± ”q/kμ samples . The hiμhest value was ”q/kμ oλ Cs. Six samples contained radioiodine over the tolerance limit oλ ”q/kμ, and six samples were over the tolerance level λor radiocaesium oλ ”q/kμ. No violation oλ the limit values was observed [ ]. Honey is considered as λood oλ minor importance. Thereλore, its survey was stopped in . From on, we analysed more than honey samples. They can be divided into two μroups honey λrom λlowers and λorest honeys included chestnut honeys . Honey λrom λlowers show only small amounts oλ contamination . to ”q/kμ radiocaesium. In λorest honey, one can λind up to ”q/kμ Cs. Sporadically, we λound violation oλ the tolerance values λor radio‐ caesium and radiostrontium. One honey λrom “ustria contained . ”q/kμ Sr and ”q/kμ Cs. These products, and especially products λrom East European countries, contain elevated contaminations even years aλter the accident at Chernobyl [ , ]. .

. Tea

“λter the Chernobyl accident, we analysed tea with γ-ray spectrometry. From samples, teas exceeded the tolerance value oλ ”q/kμ. The mean activity λound was . ± k”q/kμ radiocaesium. One tea showed ”q/kμ, a clearly elevated contamination. In the λollowinμ year, no sample exceeded ”q/kμ radiocaesium. “λter some years, the contamination levels were reduced to below ”q Cs/kμ with one exception. Contamination in black tea λrom Turkey was only slowly declininμ. Even in , almost years aλter the Chernobyl accident, the radiocaesium level reached ”q/kμ, and we λound radiostrontium in amounts oλ ”q/kμ maximum. In , our λocus was set on imported tea λrom Japan. Until the end oλ , we analysed more than tea samples cominμ λrom diλλerent preλectures in Japan. The γ-analyses proved the contamination oλ μreen tea λrom the Fukushima-Daiji NPP’s accident. “t least, part oλ the measured radiocaesium oriμinates λrom the λallout oλ the NPP’s accident. This is proven by the presence oλ the short-lived radionuclide Cs . years . In oλ investiμated tea samples, Cs was present in amounts oλ . ± . ”q/kμ. ”esides tea, other λood cateμories that are imported λrom Japan were analysed. Over the last years, we analysed more than

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λood samples Table . “s can be noticed, the radiostrontium level oλ tea is approximately ± ”q/kμ and could be λound in every tea sample analysed. This contamination mainly comes λrom the bomb’s λallout. Teas λrom other countries oλ the Far East also contain radiostrontium [ , ]. Food category

Cs

Tea

. ± < . –

Soups, miso,

“lμae

Rice and rice

< .

< .

< .

products Soja and soja

Cs .

. ±

.

. ±

< . – .

Cs

+

< . –

± .

.

Sr . ± .

± .

< . – N/“

< . – .

< . – .

. ± .

. ± .

.

< . – .

< . – .

< .

.

± .

.

± .

± . – .

N/“

< . – .

< . – .

< .

. ± .

. ± .

N/“

< .

. ± .

. ± .

N/“

< . –

< . –

. ± .

. ± .

products Cereals and cereal products Veμetables, λruits

. < . – .

Fish and λish

< .

products Divers

< .

< . – .

< . –

. ± .

. ± .

< . – .

< . – .

.

. ± .

± .

.

< . – .

± .

N/“

N/“

< . – .

“ll values in ”q/kμ. First line mean ± standard deviation oλ the activity concentrations the number oλ samples with values over the detection limit is bracketed. The total oλ analysed samples per λood cateμory is set in brackets aλter the λood cateμory name. Second line activity concentration ranμe oλ all samples. N/“, not analysed. Table . Overview oλ investiμated λood imports λrom Japan λrom

.

to

.

. Mineral and tap waters

5. 2. . Artificial radionuclides , when our laboratory started with the radioactivity survey oλ λood, water, besides milk, was the λirst λood cateμory to be monitored. ”eλore , no bomb λallout was detectable in the drinkinμ water oλ ”asel < . ”q/L radiocaesium . Just aλter the accident at Chernobyl, radioiodine and radiocaesium were detectable in small amounts oλ ± and ± ”q/L in some drinkinμ water reservoirs oλ the state oλ Jura. The production oλ drinkinμ water oλ the city oλ ”asel was never aλλected.

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5. 2.2. Natural radionuclides “λter , the λocus was set on the natural radionuclides λrom the uranium and thorium decay series. First, uranium and radium were analysed in tap and mineral waters oλ Switzerland and oλ abroad. Uranium and radium were λound in activity concentrations λrom < to m”q/L and λrom < to m”q/L, respectively. In , the Federal Oλλice oλ Health analysed more than , water samples λor their uranium content [ ]. The World Health Orμanisation WHO considers uranium as relevant in drinkinμ water because oλ its toxicity as a heavy metal. The WHO recommends a limit value oλ μμ/L m”q/L λor drinkinμ water [ ]. In Germany, the tap water λrom more than drinkinμ water plants were analysed λor their natural radionuclides. “ccordinμ to this study, the drinkinμ water oλ % oλ all plants was over the limit dose oλ . mSv/year [ ]. One possible input oλ uranium is supposed to come λrom the use oλ phosphate λertilisers in aμriculture. These λertilisers may contain uranium up to mμ U/kμ P O , which was shown by a market survey in ”asel [ ]. Our investiμation μave cause λor a national investiμation oλ the Federal Oλλice oλ “μriculture. The uranium is relatively soluble and washed λrom the λertiliser into the soil. From there, it is transλerred into μround‐ water. Surbeck [ ] estimated that the use oλ λertilisers results in the increase oλ the uranium concentration in μroundwater λrom < . to μμ/kμ. In , we analysed the tap water oλ all villaμes oλ the states oλ ”asel-Campaiμn and ”asel-City. The spectrum oλ the relevant radio‐ nuclides was expanded with Rn and Po. For uranium and radium, we λound ± m”q/ L n= and ± m”q/L n= . Radon was present in all samples in the ”ecquerel ranμe ± ”q/L . “lso, Po was present in samples in the low m”q ranμe oλ ± m”q/L [ ]. In the alpine reμions oλ southern Switzerland, the activity concentrations were somewhat hiμher due to the μeoloμical underμround [ ]. .

. Healing earths

Minerals and sediments consistinμ mainly oλ silicon dioxide quartz are known as siliceous earths. These λine, λloury mineral mixtures are deposits oλ the silica shells oλ diatoms, the main constituent oλ marine phytoplankton. The dead cells sink to the ocean λloor and λorm sedi‐ ments. These layers oλ sediment are extracted in numerous mines all over the world. Siliceous earths have a wide variety oλ uses in, λor example, the pharmaceutical and λood industries e.μ., as a λood supplement . Due to their special structural properties, λoreiμn atoms and ions are incorporated durinμ sediment λormation, such as radionuclides oλ the natural decay series oλ uranium and thorium [ ]. In , we collected some siliceous earth products on the Swiss market and analysed them with γ-spectrometry. In two products, the limit value λor natural radionuclides was exceeded ”q/kμ . Furthermore, the annual dose by reμular consumption oλ one product reached halλ oλ the permitted yearly dose oλ mSv. The Federal Oλλice λor Health Products Control, Swiss Medic, complained about these products. The company involved then withdrew the product λrom the market [ ]. “n inspection oλ the products in showed that two products λrom one producer in Germany sliμhtly exceeded the limit value. Hiμher levels oλ Ra and Ra were the reason λor this. The estimation oλ the received annual dose λrom the consumption oλ the product accordinμ to recommended amount per day as advised on the inλormation leaλlet

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enclosed would lead to . mSv/year. Healinμ earths, and also silica-based chemicals oλ chemical laboratories, remain a source λor natural radionuclides [ ]. .

. Charcoal and briquettes

In , more than , tons oλ wood pellets had to be withdrawn λrom the Italian market. The product was λrom Lithuania and was contaminated with radiocaesium ”q/kμ . The λact that such products and barbecue coals are imported λrom countries such as Ukraine or Poland motivated us to conduct this investiμation. Charcoal is produced either by charcoal burninμ oλ wood possibly contaminated by the λallout oλ Chernobyl or λrom coal mininμ. The survey oλ barbecue coals over the last years showed that there is some contamination with radiocaesium ± ”q/kμ . We could not veriλy the hiμh values λrom Italy instead, one also has to consider some radiation oλ the coals derived λrom natural radionuclides, such as radium, uranium, thorium, and lead Pb . The latter is present in activities oλ around ± ”q/kμ, which is over the limit oλ ”q/kμ oλ the ordinance oλ radioprotection. The thorium activity concentrations also reach the permitted limit oλ ”q/kμ [ , ]. ”arbeque experiments with steaks μrilled over charcoal showed only a sliμhtly contamination oλ the meat. The main activity remains in the barbeque ashes [ ]. .

. Estimation of internal doses by the consumption of contaminated food in

/

”ased on the results presented λrom our own investiμations in / , we estimated a received dose by inμestion oλ . mSv. “ main contribution came λrom contaminated veμeta‐ bles. It is not clear iλ the population λollowed an appeal and the recommendations by the μovernment to avoid the consumption oλ such contaminated veμetables. Iλ so, the dose would have been reduced to approximately . mSv. Our estimations seem to be too hiμh. The basis oλ our calculations was dominantly on the λirst months aλter the Chernobyl accident. Thus, our mean values are not representative oλ the whole years and . Table μives an overview oλ these investiμations. Origin

Activity levels +

Milk, CH

I

/ Cs

+

Activity levels Sr

+

Cow

<

Reindeer imp.


H• < / i > . This dehydroμenation process depends on the site λrom which the H atom is removed. Experimental studies with partially deuterated thymine, in which the deuterium is at either nitroμen or carbon sites, showed that hydroμen loss occurs exclusively λrom the N sites. H loss λrom the C sites is thermodynamically accessible within this enerμy ranμe, but has not been observed experimentally. Moreover, in employinμ methylated thymine and uracil, it has been shown that by adjustinμ the electron enerμy, the loss oλ H can be made even site‐selective with respect to the N and N positions. “lthouμh eV electrons induce H loss at the N position N ‐H , the process can be switched at . eV to N ‐H Figure b . These results have siμniλicant consequences λor the molecular mechanism oλ DN“ strand breaks induced by LEEs. Within DN“, the N position oλ thymine is coupled with the suμar moiety and thus λorms thymidine, which is one oλ the nucleosides. ”ecause the shapes oλ the siμnals λrom thymine and the more complex thymidine resemble each other, it can be concluded that H abstraction in thymidine predominantly occurs at the thymine moiety and, more precisely, at the N position Figure b [ ]. In addition to the detection oλ anions and the enerμies at which they are λormed, much eλλort has been expended to matchinμ particular types oλ DE“ process to speciλic resonant peaks observed in DE“ ion yields. In the case oλ the most abundant anion λormed λor all nucleobases,

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it has been proposed that these resonant peaks can be assiμned to vibrational Feshbach resonances VFRs [ , ]. VFRs usually occur at low enerμies, when vibrational levels oλ the transient anion lie below the correspondinμ vibrational states oλ the neutral, and are more expected in μreatly polarized molecules with very larμe dipole moment, which leads to a lonμ‐ ranμe attractive interaction. They may serve as a μateway λor dissociation at low enerμies iλ they are coupled with a dissociative valence state. This can be the case λor the λormation oλ dehydroμenated ions λrom nucleobases, where resonances arise λrom couplinμ between the dipole bound state and the transient anion state associated with the occupation oλ the lowest σ* orbital. Recently, the nucleobase λraμmentation oλ N–H bonds induced by LEEs was studied by employinμ the C“SPT //C“SSCF computational approach [ ]. These calculations showed that the two lowest lyinμ π* states can be determined at enerμies below . eV and above . eV λor pyrimidines, whereas λor purines, this enerμy μap between the two anionic states was less pronounced. These calculations also suμμested the possibility oλ coexistence oλ dipole‐ bound and valence‐bound processes in the low‐electron enerμy ranμe. Further to the observations oλ site selectivity in DE“ processes leadinμ to sinμle‐bond cleavaμe within a nucleobase, site selectivity also occurred in multiple‐bond cleavaμe. “s in the cases oλ both dehydroμenation oλ nucleobases and its complementary channels, which resulted in the Hˉ λormation, site selectivity was demonstrated when multiple‐bond cleavaμe was involved, λor example, λor the λormation oλ NCO‾ λrom thymine and its derivatives [ ]. This anionic λraμment was λormed in a sequential decay reaction, in which the dehydroμenated anionic nucleobase acts as an intermediate product. In this case, the remarkable resonances, which were observed λor dehydroμenation and λor H reaction channels in nucleobases, were preserved λor the subsequent decay reaction, leadinμ to the λormation oλ NCO‾ as the λinal product. In μeneral, the total cross sections λor DE“ to nucleobases exhibited comparable maμnitudes in the enerμy ranμe λor TM“ λormation [ ]. However, these cross sections were up to times smaller than those λor the λormation oλ sinμle‐strand breaks, while the cross sections λor suμar and phosphate μroup analoμs see Section . were even smaller in maμnitude. . . Sugar and phosphate group The hiμh λraμility oλ the DN“ backbone with respect to the impact oλ LEEs with low kinetic enerμy was observed λor ‐deoxy‐D‐ribose and its RN“ equivalent i.e., ribose , alonμ with their analoμs [ ]. In principle, the dissociation oλ any oλ P–O–C bonds in the suμar–phosphate backbone or C–C bond within the suμar could result in a DN“ strand break. Iλ such breakaμes were to occur via the DE“ process in DN“, then DE“ would represent an important pathway throuμh which the direct interaction oλ LEEs could aλλect bioloμically siμniλicant damaμe. The DE“ to ‐deoxy‐D‐ribose results in a stronμ decomposition oλ the suμar at electron enerμies near eV, indicatinμ the loss oλ one or more molecules oλ water [ ]. Similar λindinμs were observed λor D‐ribose and other suμars [ ], indicatinμ that DE“ at eV is a common property oλ all monosaccharides. However, the mechanisms λor DE“ reactions leadinμ to loss oλ neutral water are more complex in comparison to the dehydroμenation oλ the nucleobases, because they involve the dissociation oλ multiple bonds and/or atom rearranμement with

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simultaneous λormation oλ new bonds. Thereλore, the mechanism oλ DE“ to suμars near eV is not λully understood. It is however proposed to occur via the λormation oλ a shape€ resonance. In a suμar molecule, the extra orbital can be a σ* orbital oλ the O–H bond. “s was observed λor alcohols [ ], the σ* orbital oλ the hydroxyl μroup λor the dehydroμenation channels appears at hiμher enerμy λor simple alcohols than λor cyclic alcohols. Moreover, it was λound that larμer numbers oλ hydroxyl μroups present in a molecule could enhance the dissociation oλ an O–H bond, by decreasinμ the enerμy oλ the thermodynamic threshold. This mechanism has been suμμested λor ‐deoxy‐D‐ribose and D‐ribose, which contain three and λour hydroxyl μroups, respectively [ ]. In addition, experiments with the ribose analoμs tetrahydroλuran and ‐hydroxytetrahydroλuran showed that DE“ cross sections were μreatly enhanced by the presence oλ OH μroups [ ]. However, λor alcohols, their molecular dissoci‐ ation involved simple bond cleavaμe, while in suμars, λraμmentation oλ several diλλerent bonds occurs. One oλ the proposed models λor suμar dissociation was provided λrom ab initio calculations oλ VFRs λormed initially by a dipole‐bound state oλ suμar due to a larμe dipole moment [ ]. Other quantum chemical calculations conλirmed this model, showinμ that the suμar rinμ can convert into an open chain by intramolecular charμe transλer. This mechanism can lead to dissociation by loss oλ a water molecule, assuminμ that the barrier λor such a transλer is suλλiciently low [ ]. It was also calculated throuμh quantum dynamics scatterinμ theory that the λormation oλ shape resonances λor D‐ribose is excluded at low enerμies, but they can be λormed at hiμher enerμies [ ]. In the case oλ thymidine, in which suμar is covalently bound to thymine, the DE“ study showed two resonant structures Figure b [ ]. The one at lower enerμy was associated with a reaction in which the excess electron is initially localized in the suμar moiety, leadinμ to the μlycosidic bond cleavaμe. The second resonance was attributed to a reaction in which the excess electron was localized on the thymine moiety, resultinμ in the loss oλ a neutral H atom λrom the N site, as was mentioned λor thymine. Since nucleosides can be easily decomposed due to the elevated temperatures necessary λor evaporatinμ samples, no experimental data λor other μas‐phase nucleosides or nucleotides are reported, besides those λor thymidine [ ], cytidine [ ], and ‐deoxycytidine ‐monophosphate [ ]. Similarly, due to experimental diλλiculties, the phosphate μroup in the μas phase could not easily be investiμated as an isolated compound. Its simplest analoμ, H PO phosphoric acid , is not easily vaporized λor μas‐phase experiments or molecular deposition λor thin λilm experiments [ ]. Thereλore, to understand the DE“ process within the phosphate μroup, several compounds involvinμ phosphoric acid derivatives, λor example, dibutylphosphate and triethylphosphate [ ], were examined. DE“ to these compounds lead to P–O and C–O bond cleavaμes, which correspond to a direct sinμle‐strand break. “s λor suμars, many λraμmentation channels occurred close to eV however, these low‐enerμy channels are most likely driven by the larμe electron aλλinity oλ PO . eV . The cross sections λor DE“ to the suμar and phosphate μroup analoμs were relatively small, that is, about one maμnitude lower than those λor nucleobases [ ]. These μas‐phase results on suμars and phosphate units revealed that LEE attachment can induce sinμle‐strand breaks by electron localization either on the suμar moiety λollowed by the electron transλer to the backbone or directly on the phosphate μroup.

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. . Radiosensitizers “n important characteristic oλ many current and potential radiosensitizers used in radiother‐ apy or potential ones is a hiμh cross section λor DE“. Since haloμenated pyrimidines, mainly substituted uracil derivatives, exhibit hiμh sensitivity to electron attachment and a rich λraμmentation pattern λrom DE“, they have attracted considerable interest as radiosensitizers. From a medical point oλ view, the substitution oλ pyrimidines in the μenetic sequence oλ cellular DN“ does not aλλect the μene expression, and additionally enhances the sensitivity oλ livinμ cells to radiation. “ larμe number oλ μas‐phase experimental and theoretical studies oλ several haloμenated pyrimidines e.μ., ‐bromouracil [ – ], ‐chlorouracil [ , , , , ], ‐ λluorouracil [ , , , ], ‐iodouracil [ , ], ‐chlorouracil [ , ] were perλormed in recent years and report orders oλ maμnitude oλ hiμher cross sections λor DE“ relative to their nonsubstituted precursors. Further to the DE“ studies, other electron spectroscopic techniques and theoretical calculations at the ab initio and density λunctional theory levels were utilized to characterize electronic structure and reveal the λraμmentation mechanisms oλ haloμenated pyrimidines [ ]. These studies elucidated the enerμies oλ vertical transitions to π* and σ* orbitals, showinμ that the μround TM“ state oλ pyrimidine with the additional π* electron is a λew tens oλ eV more unstable than the neutral μround state, whereas the vertical electron aλλnities oλ the haloμenated derivatives were λound to lie close to eV. Moreover, DE“ studies revealed that the lowest π* anion states oλ the haloμenated pyrimidines λollow similar λraμmentation channels, resultinμ in the λormation oλ the halide λraμment anion. These studies also revealed that the total anion yields λor bromopyrimidine were much larμer than those measured λor the chloro‐derivatives. These results indicate that bromopyrimidines carry the μreatest potential as radiosensitizers λor damaμe by SEs, which, via DE“ to bromo‐substituted DN“, will enhance radiation‐induced damaμe to the cell. Recently, μas‐phase DE“ studies on haloμenated purines e.μ., chloroadenine [ ] and λluorinated nucleosides ‐deoxy‐ ‐ λluorocytidine and , ‐diλluorocytidine μemcitabine [ ] have been initiated to determine in what ways their radiosensitizinμ properties are derived λrom LEE‐driven chemistry. In addition to the haloμenated nucleobases, several aromatic compounds containinμ nitro μroups have been recently investiμated in the μas phase. For instance, DE“ studies perλormed λor ‐nitrouracil showed the λormation oλ a lonμ‐lived parent anion, as well as a rich λraμmen‐ tation pattern via λormation oλ either shape€ or core‐excited€ resonances at low electron enerμies [ , ]. The properties oλ ‐nitrouracil showed a radiosensitizinμ nature similar to that oλ the haloμenated pyrimidines. Interestinμly, while in the case oλ haloμenated pyrimi‐ dines, the most dominant λraμment λormed was a halide anion, that λor ‐nitrouracil is an anion oλ the pyrimidine without a nitro μroup. Thereλore, the counterpart λraμment oλ this dissoci‐ ation channel is the λormation oλ the NO radical, which is λormed in close vicinity to DN“ and can lead to the activation oλ lethal cluster damaμe in livinμ cells. There is also a μreat potential λor other nitro‐containinμ compounds such as nitroimidazolic compounds to be used in radiotherapy, since LEEs eλλectively induce their dissociation [ , ]. Similarly, their decomposition via DE“ involves a ranμe oλ unimolecular λraμmentation channels λrom simμle‐bond cleavaμes to complex reactions, possibly leadinμ to a complete deμradation oλ the tarμet molecule. However, these studies revealed that the entire rich

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chemistry induced by DE“ was completely suppressed by methylation in the electron enerμy ranμe below eV. In recent years, platinum‐based druμs were also investiμated reμardinμ their decomposition by LEEs. It was suμμested that in concomitant treatment in which chemotherapeutic druμs and radiotherapy are combined, one possible mechanism responsible λor the observed synerμy between treatments is the enhancement in the number oλ secondary species induced by primary radiation in the vicinity oλ the bindinμ site oλ the platinum compounds in DN“ see Section . The μas‐phase DE“ studies oλ Pt”r in the electron enerμy ranμe between and eV showed the λormation oλ the ”r anion via two possible channels. The most dominant channels were assiμned to the ”r‾ + Pt”r dissociation limit reached at ∼ eV and the hiμher enerμy channel to ”r‾ + Pt + ”r [ ]. The observation that all these radiosenisitizers exhibit DE“ with hiμh eλλciency, even close to eV, may have siμniλicant implications λor the development and use oλ these druμs in tumor radiation therapy. Considerinμ their use as radiosensitizers, their λraμmentation and the resultinμ μeneration oλ radicals at very low electron enerμies may be a key in understandinμ their action and the molecular mechanisms necessary to improve radiotherapy.

. Electron attachment to short single‐stranded and plasmid DNA Cellular DN“ consists oλ a double‐stranded helical structure, composed oλ two lonμ polynu‐ cleotide chains [ ]. Thus, as already mentioned in the Introduction section, in order to systematically understand LEE damaμe mechanisms and their role in radiation DN“ damaμe, molecular tarμets oλ increasinμ complexity were studied, λrom simple molecules containinμ just two oλ the basic subunits e.μ., a phosphate μroup coupled with a suμar or a nucleoside havinμ a DN“ base + suμar , via synthetic, sinμle‐ and double‐stranded oliμonucleotides, containinμ multiple nucleotides to plasmid and other cellular DN“ with many thousands oλ base pairs. Even thouμh most simple DN“ components may be easily vaporized λor experimental investiμation in the μas phase, the larμer units such as nucleosides and nucleotides usually decompose durinμ evaporation [ ]. In any case, the condensed phase is certainly the more appropriate environment to study problems relevant to radiation damaμe in biomolecular systems. The experimental methods and techniques, used in the condensed phase, diλλer λrom those in the μas phase. Most condensed phase experiments are achieved by bombardinμ thin λilms – nm oλ oliμonucleotides or plasmid DN“ with an enerμy‐selected beam oλ LEEs λrom an electron μun or an electron monochromator. To prevent excessive charμinμ, these thin‐ λilm bioloμical samples are deposited onto a metal substrate by spin‐coatinμ, lyophilisation λreeze‐dryinμ , or molecular selλ‐assembly, as in the case oλ thiolated DN“ on μold substrates [ ] and , ‐diaminopropane layer plasmid on μraphite [ ]. The LEE‐induced damaμe to plasmid and linear DN“ λilms has then been investiμated by measurinμ electron‐stimulated desorption ESD oλ anions, imaμinμ the breaks by atomic λorce and scanninμ tunnelinμ microscopies, and analyzinμ, aλter bombardment, the chanμe oλ DN“ topoloμy by μel

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electrophoresis or the molecular content by hiμh‐ perλormance liquid chromatoμraphy HPLC and mass spectroscopy [ , ]. Oliμomers oλ sinμle‐stranded DN“ containinμ the λour bases e.μ., G, C, “, and T , which are amonμ the simplest λorms oλ DN“, have made the analysis oλ deμradation products much simpler than would be the case λor lonμer sinμle‐ and double‐stranded conλiμurations. Short oliμomers deposited onto metal surλaces e.μ., tantalum, platinum, and μold as λilms oλ diλλerent thicknesses – ML were bombarded with LEEs and produced λraμments analyzed by HPLC [ ]. The results λor the GC“T oliμonucleotide indicated that strand breaks occur preλerentially by cleavaμe oλ the C–O bond rather than the P–O bond, with two maxima at electron enerμies oλ and eV [ , ]. Recently, ”ald and co‐workers demonstrated the visualization oλ LEE‐induced bond cleavaμe in DN“ oriμami‐based DN“ nanoarrays on the sinμle‐molecule level usinμ atomic λorce microscopy “FM [ – ]. This novel method has a number oλ advantaμes only miniscule amounts oλ material are required to create submonolayer surλace coveraμe, because oλ the λacility to detect the DN“ strand breaks at a sinμle‐molecule level within a sinμle experi‐ ment, more than one oliμonucleotide sequence with various arranμements can be irradiated to eλλiciently compare a number oλ diλλerent DN“ structures the method represents a simple way to obtain absolute strand break cross sections, thus providinμ benchmark values λor λurther experimental and theoretical studies, and λinally this technique is not limited to sinμle strands, but can be extended to quantiλy DS”s and to investiμate hiμher order DN“ structures. “pplyinμ this technique, ”ald and coworkers compared the absolute strand break cross sections oλ diλλerent ‐mer oliμonucleotide sequences i.e., '‐TT XTX TT, with X = “, C, or G to evaluate the role oλ the diλλerent DN“ nucleobases in DN“ strand breakaμe. They also studied the sensitizinμ eλλect oλ incorporation oλ ‐bromouracil ”rU by comparinμ the absolute strand break cross sections λor the sequences '‐TT X”rUX TT, with X = “, C, or G. The observed trend in the absolute strand break cross sections aμrees qualitatively with the previous HPLC studies investiμatinμ the λraμmentation oλ oliμonucleotide trimers oλ the sequence TXT, with X = “, C, G, irradiated with eV electrons [ ]. “dditionally, the cross sections measured with this method are comparable in maμnitude with the cross sections λor strand breaks in diλλerent plasmid DN“ molecules induced by – eV electrons, as deter‐ mined by aμarose μel electrophoresis [ , ]. The DN“ nanoarray technique thus bridμes the μap between very larμe μenomic double‐stranded DN“ and very short oliμonucleotides, and enables the detailed investiμation oλ sequence‐dependent processes in DN“ radiation damaμe. Further experimental and theoretical studies are carried out coverinμ a broad ranμe oλ electron enerμies and DN“ sequences to elucidate the most relevant damaμe mechanisms [ ]. In order to increase the complexity oλ tarμeted biomolecules, several studies have investiμated the damaμe induced by LEEs in double‐stranded plasmid DN“. Due to the supercoiled arranμement oλ plasmid DN“, a sinμle‐bond rupture in a DN“ with a λew thousand base pairs can produce a conλormational chanμe in the topoloμy oλ the entire molecule. These chanμes include base alterations, abasic sites, intra‐ and inter‐strand base cross‐links, DN“ adducts, and SS”s or DS”s hence, these can be detected eλλiciently by techniques such as μel electro‐

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phoresis. This technique can identiλy supercoiled SC , nicked circular C , λull‐lenμth linear L , cross‐linked CL , and short linear λorms oλ DN“, which can be assiμned to undamaμed DN“, SS”s, DS”s, several types oλ cross‐linked DN“, and multiple double‐strand breaks MDS”s , respectively [ ]. Thouμh it has been established that most oλ the strand breaks induced by ionizinμ radiation have been repaired by a DN“ liμation step, a DS” represents a particularly detrimental lesion that poses a serious threat to the cell, since it usually cannot be easily repaired [ ]. Indeed, even a sinμle DS” can lead to cell death iλ leλt unrepaired or, more worryinμly, it can cause mutaμenesis and cancer iλ repaired improperly [ ]. The results obtained λor LEE‐irradiated supercoiled plasmid DN“ in several investiμations are well described in the literature and summarized in authoritative review articles [ , , ]. These studies have shown that SS”s can occur as a result oλ DE“ at electron enerμies well below electronic excitation and ionization thresholds . – eV [ , ]. The results oλ Martin et al. [ ] reveal two resonant peaks at . and . eV in the SS” yield λunction i.e., the number oλ strand breaks versus the incident electron enerμy via the λormation oλ TM“s. These λindinμs are consistent with theoretical calculations indicatinμ that SS”s induced by near‐zero enerμy electrons are thermodynamically λeasible [ – ]. Theoretical simulations oλ electron scatter‐ inμ and electron capture via shape€ resonances support the role oλ LEEs in DN“ strand breaks [ ]. Theoretical calculations on scatterinμ and attachment oλ LEEs to DN“ components up to supercoiled plasmid DN“ have been intensively reviewed in recent years [ , ]. “nother spatially resolved technique that exploits the use oλ μraphene‐coated “u thin λilms and surλace‐enhanced Raman spectroscopy SERS has recently emerμed. Utilizinμ this technique, the sequence dependence oλ DN“ damaμe at excitation enerμies < eV can be studied [ ]. Currently, Ptasińska and coworkers are perλorminμ a quantitative and qualitative investiμation oλ the various types oλ damaμes to dry and hydrated DN“ induced by exposure to helium and nitroμen atmospheric pressure plasma jets “PPJs . Since an “PPJ contains multiple reactive species, includinμ LEEs, also λound in radiation chemistry, exposure to these plasma jets provides inλormation on both the direct and indirect pathways to damaμinμ DN“. Ptasińska and coworkers have employed nitroμen “PPJ to induce DN“ damaμe in SCC‐ oral cancer cells, and have thus provided new insiμht into radiation damaμe to a cellular system [ ].

. LEEs interaction with protein building blocks It is well known that within the cells, DN“ is in close contact with, and packed by, chromo‐ somal proteins histones . The attachment oλ proteins protects DN“ λrom damaμe by com‐ paction e.μ., which restricts easy access by λree radicals to DN“ and repairs some oλ the damaμe oλ electron/hydroμen donation [ ]. LEE damaμe to proteins within cells should not, by itselλ, cause siμniλicant lonμ‐term bioloμical damaμes, because proteins can be replaced. However, due to the presence oλ histones and other chromosomal proteins in the vicinity oλ DN“, reactive species produced λrom LEE interactions with protein constituents e.μ., nearby

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amino acids may in turn interact with DN“, causinμ indirect damaμe. Thus, λrom a radio‐ bioloμical point oλ view, there is considerable interest in studyinμ the action oλ LEEs on this important class oλ biomolecules [ ]. Recent work has λocused on the buildinμ blocks oλ proteins, that is, amino acids and small peptides, since the size and complexity oλ chromosomal proteins prevent direct detailed analysis oλ the λraμmentation processes induced by LEEs [ , ]. Indeed, measurinμ the λraμmentation oλ amino acids and their analoμs is no more complex than it is λor DN“ constituents see Sections and [ – ], and can help elucidate the eλλects oλ electron irradiation in larμer more complex proteins [ ]. In the recent years, several investiμations have employed soλt ionization techniques, such as matrix‐assisted laser desorption ionization M“LDI [ – ], electrospray ionization ESI [ , ], and collision‐induced dissociation CID [ – ], to study the ionization and λraμmentation oλ diλλerent amino acids and small peptides in the μas phase. Gas‐phase investiμations oλ LEE‐induced damaμe to protein subunits have been reported λor the amino acids alanine [ ], tyrosine [ ], μlycine [ , ], proline [ , ], cysteine [ ], and serine [ , ], as well as small peptides, such as dialanine [ ] and amino acid esters [ ]. For all cases, the anion yield λunctions i.e., ion yields measured as a λunction oλ electron enerμy exhibited localized maxima at enerμies below eV, indicatinμ the λormation oλ TM“s. It has been established that no intact parent anion is observable on mass spectrometric timescales aλter capture oλ a λree electron, and that the most probable reaction corresponds to the loss oλ a hydroμen atom λrom a carboxyl μroup to λorm λor a molecule M,€ the dehydro‐ μenated anion M–H ‾ at enerμies oλ around . eV [ , , , ]. Early DE“ studies ascribed this process to initial electron attachment into a π* orbital oλ the C=O bond in the COOH μroup, which couples to the repulsive σ* O–H orbital [ ]. However, recent calcu‐ lations questioned this DE“ mechanism [ ] instead, it was suμμested that direct electron capture into the purely repulsive short‐lived σ* O–H orbital, which is a very broad resonance oλ more than eV width, could be responsible λor the loss oλ the hydroμen [ ]. In the condensed phase, analyzinμ LEE‐stimulated desorption oλ anions λrom physisorbed thin λilms oλ μlycine, alanine, cysteine, tryptophan, histidine, and proline [ , ] indicated that H‾ was the major desorption λraμment, as CH ‾, O‾, and OH‾ were the λraμments produced with lower siμnals in all named amino acids. Similar results were observed in ESD experiments λrom LEE‐bombarded chemisorbed λilms, prepared by selλ‐assembled monolayers S“Ms oλ two diλλerent chains oλ Lys amide molecules [ ]. For this model oλ a seμment oλ a peptide backbone, the desorbed siμnals were dependent on the lenμth oλ the amino acid sequence. “mino acids are also suitable model molecules λor investiμatinμ the interactions oλ biomole‐ cules with metallic surλaces, particularly silver and μold. Oλ the naturally occurrinμ amino acids, only cysteine contains a thiol -SH μroup, which allows it to bind to the metal by λorminμ a S-Metal bond [ , ]. This characteristic makes cysteine an ideal model to investiμate protein interactions with μold surλaces includinμ those oλ μold nanoparticles [ , ]. “ detailed study on electron attachment to L‐cysteine/“u was recently reported by “lizadeh et al. [ , ] who measured anion yields desorbed λrom chemisorbed S“Ms and physi‐ sorbed thin λilms bombarded with sub‐ eV enerμy electrons. These ESD measurements

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showed that LEEs are able to eλλciently decompose this amino acid via DE“ and dipolar dissociation DD , when the molecule is chemisorbed via the SH μroup to a μold surλace. Reμardinμ the protective eλλect oλ amino acids on DN“ aμainst LEEs, Solomun et al. [ ] reported that the sinμle‐strand DN“‐bindinμ E. coli protein can eλλectively inhibit the λorma‐ tion oλ SS”s by ‐eV electrons in oliμonucleotides. Ptasińska et al. [ ] subsequently investi‐ μated by post‐irradiation analysis with HPLC‐UV, the molecular λraμmentation induced by ‐ eV electrons in λilms comprisinμ the GC“T tetramer and one oλ the two amino acids, μlycine and arμinine. “t low ratios R oλ amino acid to GC“T i.e., R < , particularly λor μlycine, the total oliμonucleotide λraμmentation yield unexpectedly increased. “t hiμher ratios ≤ R ≤ , protection oλ DN“ λrom damaμe by electrons was observed λor both μlycine and arμinine. Thereλore, the amino acid probably reduced electron capture by GC“T and/or the liλetime oλ the TM“ that initiates DE“ process. “ similar conclusion reμardinμ the stability oλ the amino acid side chain–nucleobase complexes can be deduced λrom the theoretical studies oλ Wanμ et al. [ ]. Wanμ and coworkers perλormed calculations at the ” LYP/ ‐ G d,p ‐level anionic hydroμen‐bonded complexes λormed between the amino acid side chains and the nucleobase μuanine. Furthermore, by studyinμ via λirst‐principles molecular dynamics simulations a model system composed oλ thymine and μlycine, Kohanoλλ et al. [ ] recently investiμated the protection oλ DN“ by amino acids aμainst the eλλects oλ LEEs. They considered thymine–μlycine dimers and a condensed‐phase model consistinμ oλ one thymine molecule solvated in amorphous μlycine. These results indicated that at room temperature, the amino acid chemically and physically perλorms the role oλ a protective aμent λor the nucleobase. In a chemical mechanism, the excess electron is λirst captured by the thymine then, a proton is transλerred in a barrierless way λrom a neiμhborinμ hydroμen‐bonded μlycine. Reducinμ the net partial charμe on the thymine molecule stabilizes the excess electron. In the physical mechanism, μlycine molecule acts as an electron scavenμer to capture the excess electron directly, which prevents the electron to be localized in DN“. Protectinμ the nucleobase via the latter mechanism requires a predisposition λor proton transλer to the oxyμen in the carboxylic acid μroup oλ one oλ the involved amino acids. Consequently, raisinμ the λree‐enerμy barrier associated with strand breaks, prompted by these mechanisms, can halt λurther reactions oλ the excess electron within the strand oλ DN“, λor instance, transλerrinμ the electron to the backbone which leads to induce a strand break in DN“. Increasinμ the ratio oλ amino acid to nucleic acid will enhance the protectinμ role oλ amino acids, and accordinμly will decrease the induction oλ DN“ strand breaks by LEEs, as shown experimentally [ , ].

. LEEs interaction and induced damage under cellular conditions The μas‐ and condensed‐phase experiments with DN“ and its constituents discussed previ‐ ously were perλormed under ultrahiμh vacuum UHV conditions to permit use oλ electron beams and mass spectrometry, and to better control the molecular environment. While such experiments provide inλormation on the direct eλλects oλ LEEs, they do not reveal how LEEs

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can indirectly damaμe DN“. Comparatively, due to the experimental diλλiculties related to the production and observation oλ LEEs in aqueous media, studies on the indirect damaμe oλ LEEs to DN“ have not been μreatly developed. Ideally, to understand how the λundamental mechanisms in LEE–DN“ interactions are adapted in livinμ cells, the experimental studies should be extended to the more complex dynamic molecular environment oλ the cell, or more realistic ones, λor the DN“ molecule that contains essentially water, oxyμen, histones, and DN“‐bindinμ proteins [ ]. For instance, in the work oλ Ptasińska and Sanche [ ], the ESD yields oλ diλλerent anions desorbed by – eV electron impact on GC“T λilms were measured under an aqueous condition, correspondinμ to . molecules oλ water per nucleotide. Their experiments demonstrated that addinμ water to dry DN“ results in the bindinμ oλ the molecule to the phosphate μroup at the neμatively charμed oxyμen [ ], and then λormation oλ a complex oλ tetramer and a water molecule DN“•H O . This complex permits the λormation oλ a new type oλ dissociative core‐excited TM“ located on the phosphate μroup, which decays by O‾ desorption under electron impact via a resonance at – eV and by OH‾ desorption λrom breakinμ the P–O bond. H‾ also desorbs by dissociation oλ a TM“ oλ the complex which causes bond cleavaμe on the H O portion. Moreover, LEE‐induced damaμe to DN“ via DE“ enhances by a λactor oλ about . when an amount oλ water correspondinμ to % oλ the λirst hydration layer is added to vacuum‐ dried DN“. “lthouμh the maμnitude oλ this enhancement is considerable, it is still much smaller than the modiλication in yields oλ products produced by the λirst hydration layer surroundinμ the DN“ durinμ the radiochemical events that λollow the deposition oλ the enerμy oλ LEE in irradiated cells. Theoretical and experimental studies were concurrently carried out on the diλλraction oλ – eV electrons in hydrated ”‐DN“ '‐CCGGCGCCGG‐ ’ and “‐DN“ '‐CGCG““TTCGCG‐ ’ sequences by Orlando et al. [ ]. They postulated that compound H O•DN“ states may contribute to the modiλication oλ strand breaks yield λunctions [ , ]. Furthermore, Orlando et al. noted that lowerinμ oλ the threshold enerμy λor DS”s below eV may be correlated with the presence oλ these compound states. In this case, an initial core‐ excited€ resonance would autoionize, yieldinμ electronically excited water‐derived states and a low‐enerμy electron. The electronically excited state dissociates λorminμ reactive O, OH, and H, which can lead to suμar–phosphate bond breakaμe. The slow electron could moreover scatter inelastically within a limited mean λree path and excite a shape€ resonance oλ a base on the opposite strand. The combination oλ these two enerμy‐loss channels could lead to a DS”. This type oλ DS” requires the presence oλ water and is diλλicult to be repaired due to the close proximity oλ damaμe sites. Recent work usinμ μraphene‐coated μold thin λilms also siμnaled the siμniλicance oλ the existence oλ water molecules in DN“ damaμe mediated by shape€ resonances [ ]. This is likely due to the inλluence oλ water on lowerinμ the barrier λor charμe transλer λrom the base to the suμar–phosphate bond. In addition, the bindinμ interaction oλ DN“ with μraphene allows direct couplinμ to the phosphates as well as more direct scatterinμ with the μuanine and adenine bases. Electrons that have not been captured by DN“ bases can be captured by μraphene and immediately transλerred over nm within < . ps. The environmental or μraphene substrate interactions are critical, and at least two mechanisms occur simultaneously

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durinμ DN“ damaμe on monolayer μraphene direct base capture and ballistic transλer λrom the μraphene. “n alternative approach to simulate cellular conditions has been recently developed by “lizadeh et al. [ ] to investiμate LEE‐induced DN“ damaμe under atmospheric conditions and at various levels oλ humidity and oxyμen. Thin λilms oλ plasmid DN“ deposited on tantalum and μlass substrates were exposed to “l Kα X‐rays oλ . keV. The μeneral λeatures oλ the photo‐ejected SE λrom the metallic surλaces exposed by primary X‐ray photons are well understood in particular, more than % oλ SEs emitted λrom tantalum lie below eV and the enerμy distribution peaks around . eV, with an averaμe enerμy oλ . eV [ ]. Whereas the damaμes induced in DN“ deposited on μlass are due to soλt X‐rays, those arisinμ λrom DN“ deposited on tantalum result λrom the interaction oλ X‐rays + LEEs. The diλλerence in the damaμe yields measured in the samples deposited on two diλλerent substrates is ascribed to the interaction oλ LEEs with the DN“ and its nearby atmosphere. “lizadeh and Sanche [ ] employed this technique to examine how the presence oλ several cellular components such as, O , H O and O /H O modulates the LEE‐induced damaμe to DN“ molecules. They observed that λor hydrated DN“ λilms in an oxyμenated environment, the additional LEE‐induced damaμe that results λrom the combination oλ water and oxyμen exhibits a super‐additive eλλect, which produces a yield oλ DS” almost seven times hiμher than that obtained by X‐ray photons. More recently, they reported the λormation oλ λour radiation‐ induced products λrom thymidine by soλt X‐rays and LEEs, speciλically base release, and base modiλication includinμ ‐HMdUrd, ‐FordUrd, and , ‐DHT [ ]. Oλ the products analyzed, thymine release was the dominant channel arisinμ λrom N‐μlycosidic bond cleavaμe involvinμ π* low‐lyinμ TM“. “ LEE‐mediated mechanism was proposed to explain observation oλ ‐ HMdUrd and ‐FordUrd products, which involve loss oλ hydride ‐H‾ λrom the methyl μroup site via DE“. G‐values derived λrom the yield λunctions indicate that λormation oλ λree thymine, ‐HMdUrd, and ‐FordUrd are promoted by an oxyμen environment rather than a nitroμenous atmosphere, since the numbers and reactivity oλ radicals and ions are λormed via interactions oλ radiation with O , and are considerably larμer than under N . Moreover, O can additionally react with C‐centered radicals, thereby λixinμ€ or renderinμ the damaμe permanent. In contrast, no , ‐DHT was detected when samples were irradiated under an O atmosphere, indicatinμ that O molecules react with an intermediate radical compound, thereby inhibitinμ the pathway λor , ‐DHT λormation [ ]. Recently, novel decay mechanisms λor electronic excitations and correlated electron interac‐ tions have become subjects oλ intense study. Just over a decade aμo, Cederbaum et al. [ – ] proposed an ultraλast relaxation process in inner valence levels, which occurs in molecular systems with weakly bound λorces, such as van der Waals λorces or hydroμen bondinμ. This mechanism reλerred to as intermolecular Coulomb decay ICD is possible mainly due to the couplinμs and interactions induced by the local environment. Unlike most ionization proc‐ esses, ICD results in the ejection oλ an electron λrom the neiμhbor oλ an initially ionized atom, molecule, or cluster [ ]. The enerμy oλ the ICD electron is low, typically less than eV. ICD is expected to be a universal phenomenon in weakly bound aμμreμates that contain liμht atoms and may represent a hitherto unappreciated source oλ LEEs. Thouμh most ICD measurements

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have concentrated on rare μas clusters, new sophisticated experimental approaches have detected ICD in larμe water clusters [ ] or at condensed‐phase interλaces containinμ water dimers and clusters [ ]. Random damaμe to cellular biomolecules such as DN“ is associated with the onset oλ cancer, whereas the controlled tarμeted local release and interactions oλ LEEs can be used as eλλective therapeutic cancer treatment aμents. Since ICD is a source λor the ejection oλ slow electrons, it has been proposed that ICD could play a role in the induction oλ SS” and DS” in DN“ [ ]. Estimation by Grieves and Orlando [ ] indicated that ICD may represent up to % oλ the SS” probability λor enerμy depositions > eV and ionization events directly at the DN“–water interλace. Since the λormation oλ DS”s requires excitation enerμies > eV, the impact on DS”s is expected to be much lower. Iλ ICD contributes siμniλicantly to DN“ damaμe, this could be exploited durinμ X‐ray treatment oλ cancer. Figure schematically shows that how utilizinμ oλ X‐ray interactions with μold nanoclusters within livinμ cells, which subsequently results in releasinμ both “uμer and ICD electrons, has been suμμested as a potential strateμy λor tarμeted cancer treatment [ ].

Figure . a Resonant “uμer decay process λollowinμ X‐ray excitation. “ second process known as interatomic or in‐ termolecular Coulomb decay ICD can also occur, leadinμ to the ejection oλ slow electrons and adjacent holes. b Pos‐ sible exploitation oλ “u nanoparticles and ICD in the controlled radiation damaμe oλ cells [ ].

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“λter such extensive studies on LEE‐induced damaμe under near€‐cellular conditions, it was only very recently that the lethal eλλects oλ LEEs in cells have been demonstrated by Sahbani et al. [ ], who investiμated the bioloμical λunctionality oλ DN“, via a simple model system comprisinμ E. coli bacteria and plasmid DN“ bombarded by LEEs. In these experiments, hiμhly ordered DN“ λilms were arranμed on pyrolytic μraphite surλace by molecular selλ‐assembly technique usinμ , ‐diaminopropane ions to bind toμether the plasmid DN“s [ ]. This assembly technique mimics somewhat the action oλ amino μroups oλ the lysine and arμinine amino acids within the histone proteins. These authors measured the transλormation eλλiciency

Figure . a Variation oλ transλormation eλλiciency oλ E coli by pGEM Zλ ‐ plasmids irradiated by . – eV electrons at a λluence oλ × electrons/cm . The vertical axis is inverted. Eλλective yield λunctions λor b sinμle‐strand breaks SS”s , c double‐strand breaks DS”s , and d DN“ cross‐links [ ].

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oλ E. coli JM bacteria essentially the number oλ bacterial colonies μrown in an antibiotic environment aλter insertion into the cells oλ [pGEM‐ Zλ ‐ ] plasmid, which when undamaμed, can conλer resistance to the antibiotic ampicillin. ”eλore transλormation, the plasmids were irradiated with electrons oλ speciλic enerμies in the enerμy ranμe . – eV [ ]. Cells receivinμ severely damaμed plasmids will not μrow, and the transλormation eλλiciency will be reduced. The loss oλ transλormation eλλiciency plotted as a λunction oλ electron enerμy is shown in Figure . It reveals maxima at . and . eV, coincident with the maxima observed in the yields oλ DN“ DS”s, which were attributed to the λormation oλ core‐excited TM“s. These results indicated that the eλλects oλ TM“s are observable in the electron‐enerμy dependence oλ bioloμical processes with neμative consequences λor cell viability. The result provides λurther evidence that LEEs play important roles in cell mutaμenesis and death durinμ radiotherapeutic cancer treatment [ ].

. Role of LEEs in radiosensitization and radiation therapy “ major impetus λor achievinμ a better understandinμ oλ the action oλ ionizinμ radiation in bioloμical systems relates to applications in radioprotection and radiotherapy. Since LEEs play a major role in transλerrinμ the enerμy oλ the initial hiμh‐enerμy particle or photon to initiate all subsequent chemistry in irradiated media, understandinμ their interaction with biomole‐ cules is now beinμ recoμnized as a crucial and essential step toward such applications. “s seen λrom Section , in the last decades, our expandinμ knowledμe oλ LEE–DN“ interactions has been applied to experiments involvinμ known radiosensitizers. ”oth at the theoretical and experimental levels, this work served to suμμest new compounds havinμ radiation‐damaμe enhancinμ properties and to explain the details oλ their response to hiμh‐enerμy radiation either alone or when bound to DN“ i.e., the main tarμet λor cell killinμ in radiotherapy . . . Transient anions in halogen compounds ”romouracil, which can replace thymine in DN“ durinμ cell replication, and bromouridine were the λirst radiosensitizinμ candidates to be investiμated theoretically and experimentally with LEEs. The studies [ – ] conλirmed the prediction oλ Zimbrick and coworkers [ ] that the radiosensitizinμ properties oλ these compounds arose λrom DE“ oλ solvated electrons, and λurther showed that DE“ oλ hiμher enerμy – eV electrons was also involved in radiosensitization. Platinum bromide, aromatic compounds containinμ nitro μroup and other haloμenated thymidine derivatives were λound to play similar roles [ , , , – , , ]. Followinμ early investiμations with solvated electrons [ ], a relatively larμe number oλ experiments have been perλormed both in the μas see Section . and condensed phases [ , , ] to study electron scatterinμ λrom––and attachment to––haloμenated pyrimidines. Several experiments were perλormed usinμ S“Ms oλ ”rdU‐containinμ oliμonucleotides [ , , ]. These included the detection oλ the electron‐stimulated desorption oλ ion and neutral species and HPLC analysis oλ damaμed λilms, as well as electronic and vibrational electron‐ enerμy loss spectra λor μaseous bromouracil [ ]. These studies revealed that the radiosensi‐

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tization properties oλ haloμen compounds are more complicated than previously anticipated [ ]. Within the – eV enerμy ranμe, resonant electron scatterinμ mechanisms with halour‐ acils lead to more complex molecular λraμmentation than that occurs with thymine, which produces a diλλerent ranμe oλ anionic and neutral radical λraμments. When λormed within DN“, such λraμments could react with local subunits, and thus lead to lethal clustered damaμe, λurther to that already occurrinμ in unsensitized DN“. The most strikinμ evidence oλ a huμe enhancement oλ LEE damaμe obtained upon ”r substitution in thymine is seen in the early results oλ Klyachko et al. [ ], who λound that, in the presence oλ water, DE“ to bromouracil could be enhanced by orders oλ maμnitude compared to the dry compound. Diλλerences between wet and dry TM“ states oλ haloμenated pyrimidines have recently been investiμated by Chenμ et al. [ ]. They applied Koopman's theorem in the λramework oλ lonμ‐ranμe corrected density λunctional theory λor calculation oλ the TM“ states and selλ‐consistent reaction λield methods in a polarized continuum to account λor the solvent. Their results indicate that the TM“s oλ these molecules are more stable in water, but to diλλerinμ deμrees. The radiosensitization properties oλ halouracils depend not only on hydrated electrons, but also on LEEs and on DE“. However, the hiμh propensity oλ LEEs oλ very low enerμies i.e., < eV to λraμment bromouracil and deoxybromouridine ”rUdR may, accordinμ to the theory, exist only in sinμle‐stranded DN“ [ ]. This important prediction was conλirmed by Cecchini et al. [ ] λor the case oλ solvated electrons and was commented upon by Sevilla [ ]. Solutions oλ sinμle‐ and double‐stranded oliμonucleotides, and oλ double‐stranded oliμos containinμ mismatched bubble reμions, were irradiated with γ‐rays, and the concentrations oλ various reactive species produced, includinμ solvated electrons, were controlled with scav‐ enμers. When in the absence oλ oxyμen, OH radicals were scavenμed, ”rUdR was shown to sensitize sinμle‐stranded DN“, but could not sensitize complementary double‐stranded DN“. However, when ”rUdR was incorporated in one strand within a mismatch bubble, the nonbase‐paired nucleotides adjacent to the ”rUdR, as well as several unpaired sites on the opposite unsubstituted strand, were hiμhly sensitive to γ‐irradiation. Since LEEs and solvated electrons λraμment ”rUdR by the same DE“ mechanism [ – , ], these results imply that the stronμ sensitizinμ action oλ ”rUdR to electron‐induced damaμe is limited to sinμle‐ stranded DN“, which can be λound in transcription bubbles, replication λorks, DN“ bulμes, and the loop reμion oλ telomeres. These results are clinically relevant since they suμμest that ”rUdR sensitization should be μreatest λor rapidly proliλeratinμ cells [ , ]. When injected into a patient beinμ treated λor cancer, ”rUdR quickly replaces a portion oλ the thymidine in the DN“ oλ the λast‐μrowinμ maliμnant cells, but radiosensitization occurs only when DN“ is in a sinμle‐stranded conλiμuration e.μ., at the replication λorks durinμ irradiation . From this conclusion, it appears advantaμeous to administer to patients receivinμ ”rUdR, another approved druμ, such as hydroxyurea, to increase the duration oλ the S‐phase oλ cancer cells i.e., the replication cycle . This addition would increase the probability that SEs would interact with bromouracil while bound to DN“ in its sinμle‐strand λorm. Such a modality provides an example oλ how our understandinμ the mechanisms oλ LEE‐induced damaμe can help to improve radiotherapy [ ].

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. . Transient anions in DNA bound to platinum chemotherapeutic agents Considerinμ that it can oλten take years, iλ not decades, beλore potential new radiosensitizers arrive in the clinic, Zhenμ et al. [ ] hypothesized that present clinical protocols involvinμ hiμh‐enerμy radiation and platinum Pt chemotherapeutic aμents could be improved by considerinμ the λundamental principles oλ enerμy disposition, includinμ the results oλ LEE experiments. Their initial μoal was to explain the superadditive eλλect occurrinμ in tumor treatments, when cisplatin and radiation were administered in concomitance [ , ]. Zhenμ et al. [ ] λound that, with cisplatin bound to DN“ as in the cancer cells, damaμe to the molecule increases by λactors varyinμ λrom . λor hiμh‐enerμy electrons to . at eV. Considerinμ the much hiμher enhancement λactor EFs at eV, the increase in bond disso‐ ciation was interpreted as beinμ triμμered by an increase in DN“ damaμe induced by LEEs. In their experiments, Zhenμ et al. [ ] deposited lyophilized λilms oλ pure plasmid and plasmid–cisplatin complexes on a clean tantalum λoil. The λilms were bombarded under UHV with electrons oλ – keV. Under these conditions, % oλ the plasmid–cisplatin complexes consisted oλ a cisplatin molecule chemically bound to DN“, preλerentially at the N atom oλ two μuanines producinμ an interstrand adduct. The λilms had the necessary thickness to absorb most oλ the enerμy oλ the electrons. The diλλerent λorms oλ DN“ correspondinμ to SS”s and DS”s were separated by μel electrophoresis, and the percentaμe oλ each λorm quantiλied by λluorescence. Exposure response curves were obtained λor several incident electron enerμies λor cisplatin bound or not to plasmid DN“. Table μives the results λor exposure to , , , and , eV electrons oλ λilms oλ pure DN“ and cisplatin/plasmid complexes with a ratio R oλ and . For both R values, cisplatin bindinμ to DN“ increases the production oλ SS”s and DS”s, but in quite diλλerent proportions dependinμ on electron enerμy. Considerinμ that it takes about eV to produce a DS” with electrons [ ], the most strikinμ result oλ Table is clearly the production oλ DS”s by eV electrons. Later, Rezaee et al. [ ] demonstrated that even . eV electrons could induce DS”s in DN“ containinμ Pt adducts in similar proportions and more eλλiciently than other types oλ radiation, includinμ X‐rays and hiμh‐enerμy electrons. The λormation oλ DS”s by . eV electrons resulted λrom a sinμle‐hit process. Gamma radiolysis experiments with plasmid DN“ dissolved in water, λurther demonstrated that even solvated electrons could react with cisplatin–DN“ complexes to induce DS”s [ ]. The results oλ Zhenμ et al. [ ] at hiμher enerμy were later conλirmed by those oλ Rezaee et al. [ ], who showed that increased damaμe via the λormation oλ TM“ could explain, at least partially, the concom‐ itance eλλect in chemoradiation therapy λor cisplatin, as well as λor the other platinated chemotherapeutic druμs such as oxaliplatin and carboplatin. This type oλ radiosensitization was investiμated in more detail by irradiatinμ with a γ source the oliμonucleotide TTTTTGTTGTTT with or without cisplatin bound to the μuanines [ ]. Usinμ scavenμers and by eliminatinμ oxyμen, the oliμonucleotide was shown to react with hydrated electrons. Prior to irradiation, the structure oλ the initial cisplatin adduct was identiλied by mass spectrometry as G‐cisplatin‐G. Radiation damaμe to DN“ bases was quantiλied by HPLC, aλter enzymatic diμestion oλ the TTTTTGTGTTT–cisplatin complex to deoxyribonucleosides. Platinum adducts were λollowinμ diμestion and separation by HPLC, quantiλied by mass spectrometry. The results demonstrated that hydrated electrons induce

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damaμe to thymines as well as detachment oλ the cisplatin moiety λrom both μuanines in the oliμonucleotide. The amount oλ λree cisplatin i.e., the cleavaμe oλ two Pt–G bonds was λound to be much larμer than that oλ the products resultinμ λrom the cleavaμe oλ a sinμle bond [ , ]. Form of damage

SSB

DSB

Energy eV

,

,

Thickness

ML

nm

DNA

±

± .

. ± .

ND

±

±

. ± .

Cisplatin:DNA = :

±

±

±

. ± .

±

±

±

. ± .

Cisplatin:DNA = :

±

±

±

. ± .

±

±

±

. ± .

±

ML

nm

ND, Not detected. The errors represent the deviation oλ three identical measurements. Table . Yields in ‐ electron‐ molecule‐ λor the λormation oλ SS” and DS” induced by , , and eV electron impact on ML DN“ λilms and keV electron impact on nm DN“ λilms deposited on a tantalum substrate.

These results suμμest two major pathways by which hydrated electrons interact destructively with TTTTTGTGTTT–cisplatin [ , ]. First, the hydrated electron is captured initially on a thymine base and is transλerred to the μuanine site by base to base electron hoppinμ, where DE“ detaches the cisplatin moiety λrom the oliμonucleotide. “lternatively, the hydrated electron interacts directly with the platinum–μuanine adduct, and cisplatin is detached via DE“. These hypotheses were consistent with those proposed by Rezaee et al. [ ] λor LEE‐ induced damaμe to plasmid DN“. “dditionally, Rezaee et al. suμμested that in the double‐ stranded conλiμuration, the cisplatin molecule weakens many oλ the DN“ chemical bonds and chanμes the topoloμy oλ the molecule these modiλications render DN“ much more sensitive to damaμe over larμe distances [ ]. Oλ course, under hiμh‐enerμy irradiation conditions, the increase in ionization cross section, due to the presence oλ the Pt atom, also increases the quantity oλ LEEs near cisplatin and thereλore may indirectly contribute to the increase in damaμe. More recently, the enerμy dependence oλ conλormational damaμe induced to pure plasmid DN“ [ ] and cisplatin–plasmid DN“ complexes [ ] was investiμated in the ranμe – eV. In addition to the stronμ resonances i.e., TM“s in pure DN“ around and eV, λurther TM“ speciλic to cisplatin‐modiλied DN“ were observed in the yield λunction oλ SS”s at . and . eV. Moreover, the presence oλ cisplatin lowered the threshold enerμy λor the λormation oλ DS”s to . eV, considerably below that observed with electrons in pure DN“ λilms. In all cases, the measured yields were larμer than those measured with nonmodiλied DN“. To reconcile all existinμ results startinμ λrom those obtained with hydrated electrons to those μenerated up to eV, ”ao et al. [ ] suμμested a sinμle mechanism that could apply to shape and core‐excited resonances, dependinμ or not iλ electronic excitation oλ the Pt or μuanines was involved in TM“ λormation. This mechanism, previously proposed λor shape resonances by

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Rezaee et al. [ ], can be explained with reλerence to Figure . When the TM“ is λormed on the Pt adduct, the extra electron is delocalized and occupies simultaneously, with identical wave λunctions, the two bonds linkinμ the Pt atom to μuanine bases on opposite strands. Occupancy oλ the dissociative σ* orbitals induces equal repulsive impulses on the two bonds between platinum and μuanines Pt–G , due to the symmetrical delocalization oλ the excess electron. Iλ the extra electron autodetaches when the μained kinetic enerμy is larμer than the enerμy barrier to dissociate the Pt–G bonds, both bonds can be simultaneously broken. The extra enerμy λor dissociation is supplied to the complex by autodetachment λrom the σ* bond, leavinμ the additional electron stabilized at the bottom oλ the potential well oλ the Pt. The simultaneous cleavaμe oλ two Pt–G bonds and λormation oλ two μuanine radicals are λollowed

Figure . Possible mechanism λor the λormation oλ a DS” by a sinμle electron, when cisplatin links two μuanine G bases on opposite strands. a Electron capture into two identical dissociative orbitals between Pt and two Gs. b The transient anion thus λormed dissociates, leavinμ the electron on the NH Pt moiety and causinμ simultaneous cleav‐ aμe oλ the two symmetrical Pt–G bonds. The resultinμ two μuanine radicals G● abstract hydroμen λrom the back‐ bones, causinμ cleavaμe oλ phosphodiester bonds on opposite strands. c Resultinμ DS” [ ].

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by hydroμen abstraction λrom the backbone. This abstraction cleaves the phosphodiester bonds in opposite strands, λorminμ a DS”. Considerinμ the results obtained with carboplatin and oxaliplatin [ ], which are similar to those obtained with cisplatin, the mechanism depicted in the diaμram oλ Figure is likely to apply also to these chemotherapeutic druμs. Since these latter behave as cisplatin and bind similarly to DN“, we can replace cisplatin by carboplatin in Figure to represent oxaliplatin in the λiμure, NH has to be replaced by C H NH . The LEE enhancement mechanism oλ damaμe in DN“–Pt druμ complexes acts on a λemtosec‐ ond timescale, which quite unlike other bioloμical mechanisms oλ radiosensitization, act over macroscopic times that can ranμe λrom hours to days. These considerations imply that the mechanism e.μ., physicochemical vs bioloμical oλ radiosensitization by Pt aμents in concom‐ itant chemoradiation therapy may be sensitive to the timinμ between the injection oλ the druμ to the patient and the irradiation. Thus, iλ TM“ λormation in DN“ plays a major role in radiosentization by Pt druμs, maximal cancer cell killinμ should be achieved, iλ these cells are irradiated when the maximum amount oλ Pt is bound to their nuclear DN“. Led by this hypothesis, Tippayamontri et al. [ , ] determined the optimal conditions λor concomitant chemoradiation treatment oλ colorectal cancer with cisplatin, oxaliplatin, and their liposomal λormulations Lipoplatin and Lipoxal [ , ]. Usinμ an animal model oλ human colorectal cancer, they determined the time window λor maximum radiosensitization and synerμy with irradiation, by studyinμ the pharmacokinetics and time‐dependent intra‐ cellular distribution oλ the Pt druμs. This, in turn, is determined by the reaction kinetics oλ the druμ with DN“ and the DN“ repair kinetics. In nude mice bearinμ HCT colorectal carcinoma, treated with the Pt druμs, they measured by inductively coupled plasma mass spectrometry, the platinum accumulation in blood, serum, diλλerent normal tissues, tumor, and diλλerent tumor cell compartments, includinμ the amount oλ Pt bound to nuclear DN“ [ , ] Figure a indicates the positions oλ bindinμ oλ cispelatin to DN“. Examples oλ the amount oλ cisplatin and Lipoplatin bindinμ to the DN“ oλ HCT colorectal cancer cells in mice are shown in Figure b as a λunction oλ time aλter injection oλ the druμ. Radiation treatment Gy was μiven , , and h aλter druμ admin‐ istration. The resultinμ tumor μrowth delay was reported and correlated with apoptosis analyses. Optimal survival oλ the mice and hiμhest apoptosis were observed when radiation was μiven at or h aλter druμ injection. These times corresponded to the times oλ maximal platinum bindinμ to tumor DN“, as shown in Figure b λor cisplatin and Lipoplatin. When tumor irradiation was perλormed at h, the ratio oλ tumor μrowth delay λor the μroup havinμ the combined treatment compared to delay λor the μroup treated with chemotherapy alone varied λrom . to . , dependinμ on the druμ. The most eλλicient combination treatment was observed when the amount oλ Pt druμ bindinμ to DN“ was hiμhest, as predicted λrom λundamental considerations [ – ]. Such results testiλy our λundamental understandinμ oλ the mechanisms oλ platinum‐induced radiosensitization and should have siμniλicant impact on the desiμn oλ more eλλicient treatment protocols.

Transient Anions in Radiobiology and Radiotherapy: From Gaseous Biomolecules to Condensed Organic and Biomolecular Solids http://dx.doi.org/10.5772/63293

Figure . a Diverse sites oλ intrastrand and interstrand bindinμ oλ cisplatin to cellular DN“. b Concentration oλ Pt– DN“ adducts in the nucleus oλ human colorectal cancer cells oλ mice bearinμ HCT xenoμraλts, as a λunction oλ time aλter administration oλ cisplatin and LipoplatinTM. The mice were irradiated at , , and h aλter injection oλ the che‐ motherapeutic aμents.

. . Interaction of LEEs with DNA bound to gold nanoparticles So λar in this section, we have shown that cancer cells can be made more sensitive to hiμh‐ enerμy radiation by chemically modiλyinμ their nuclear DN“ with small molecules. These latter provide at least some oλ their radiosensitizinμ action, by increasinμ the interaction oλ LEEs with DN“, the products oλ DE“, and the resultinμ induced damaμe. “nother approach consists oλ simply increasinμ the numbers oλ LEEs near the DN“ oλ cancer cells. The best examples oλ this type oλ radiosensitization have been provided by the numerous λundamental, in vitro, and in vivo investiμations oλ enhanced radiation absorption by μold nanoparticles GNPs . ”oth in vitro and in vivo experiments [ – ] have shown radiation enhancement eλλects due to the presence oλ GNPs. Several models have been developed to account λor dose enhancement in cells by considerinμ the increase in radiation enerμy deposition [ – ], due to additional enerμy absorption by the GNPs, as a λunction oλ their size. “s expected, the enerμy oλ electrons emanatinμ λrom the GNPs is inversely proportional to their diameter. Many models [ – ] take into account localized eλλects oλ “uμer‐electron cascades. They consider the huμe enhancement oλ enerμy deposited in the vicinity oλ GNPs, as arisinμ λrom the considerable increase in photoelectric absorption cross section oλ μold in comparison to that oλ tissue [ , , , ]. The increase in this cross section produces an additional local μeneration oλ photoelectrons, “uμer electrons, and characteristic X‐rays [ , ]. The major portion oλ the enerμy absorbed by the GNPs is converted into electrons, most oλ which escapes the GNPs with low enerμy – eV [ – ].

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The indirect eλλect oλ emitted electrons was investiμated in water solutions containinμ GNPs, where the nanoparticle‐induced OH concentration λrom radiolysis was measured. Relevant literature and details can be λound in the paper oλ Sicard‐Roselli et al. [ ], who also proposed a new mechanism λor hydroxyl radical production in irradiated GNP solutions. The direct eλλect oλ hiμh‐enerμy radiation on DN“, resultinμ λrom the presence oλ GNPs, was λirst investiμated by Zhenμ and coworkers [ , – ]. Relatively thick ~ . and . μm λilms oλ plasmid DN“ with or without electrostatically bound GNPs were bombarded with keV electrons. The probabilities oλ λormation oλ SS”s and DS”s λrom the exposure oλ and GNP–plasmid mixtures to λast electrons increased by a λactor oλ about . , compared to DN“ alone. It was suμμested that the additional damaμe in the presence oλ GNPs was μenerated by LEEs escapinμ the nanoparticles. This hypothesis was later veriλied experimen‐ tally by the work oλ Xiao et al. [ ]. These authors investiμated the radiosensitization eλλiciency in terms oλ DN“ damaμe as a λunction oλ the lenμth oλ a liμand bound at one end to the surλace oλ the GNP and at the other to DN“. They used the same DN“ λilm preparation as in the experiments oλ Zhenμ et al. [ ] and measured the ratio oλ induced damaμe with GNPs to that without GNPs i.e., the enhancement λactor, EF λor diλλerent lenμths oλ the liμand. “s indicated in Figure λrom their work, the correspondinμ EFs induced by keV electrons on plasmid DN“ bound to GNPs oλ various coatinμs ranμe λrom . to . and . , dependinμ on the lenμth oλ liμand separatinμ the μold surλace λrom the plasmid. This lenμth ranμed λrom to . and nm, respectively. The attenuation by the coatinμ oλ short‐ranμe LEEs emitted λrom the GNPs could explain the decrease in radiosensitization with increasinμ lenμth oλ the liμand [ ]. Since the attenuation ranμe oλ LEEs is shorter than about nm, it is obvious that the emission oλ LEEs λrom the GNPs and LEE‐interaction with DN“ plays a major role in the mechanism oλ GNP radiosensitization. Later, similar DN“–GNP λilms were bombarded with electrons oλ enerμies below the ioniza‐ tion potential oλ DN“. In this case, essentially no secondary LEEs were emitted λrom the DN“ and the μold surλace, so that Yao et al. [ ] could investiμate the purely chemical radiosensi‐ tization induced by GNPs. They showed that even without the emission oλ photoelectrons, direct electrostatic bindinμ oλ an averaμe oλ . – GNPs to DN“ could increase sensitization to LEEs by λactors varyinμ λrom . to . Since GNPs increase the local density oλ LEEs and cisplatin enhances LEE interactions with DN“ and damaμe to the molecule, it seemed likely that bindinμ GNPs to a cisplatin–DN“ complex would λurther boost radiosensitization and DN“ damaμe induced by cisplatin [ ]. This hypothesis was veriλied by irradiatinμ with keV electrons, GNPs electrostatically bound to a cisplatin–DN“ complex [ ]. Dry λilms oλ bare plasmid DN“ and DN“–cisplatin, DN“–GNP, and DN“–cisplatin–GNP complexes were irradiated [ ]. The yields oλ SS”s and DS”s were measured as described in the protocol established by Zhenμ et al. [ ]. When the ratio oλ GNP to DN“ was and that λor cisplatin to DN“ was , the EFs λor SS”s were between and . . With a cisplatin to GNP to plasmid ratio oλ , the EF increased to . This small increase could only be additive and unrelated to the interaction oλ additional LEEs with cisplatin. For DS” λormation, however, the bindinμ oλ both GNPs and cisplatin to a DN“ molecule produced an impressive increase in the EF, that is, DS”s were increased by a λactor

Transient Anions in Radiobiology and Radiotherapy: From Gaseous Biomolecules to Condensed Organic and Biomolecular Solids http://dx.doi.org/10.5772/63293

oλ . with respect to pure DN“. It appeared quite obvious that the additional DS”s in the cisplatin–DN“–GNP complex arose λrom the μeneration oλ additional secondary electrons λrom the GNPs. The synerμy between GNPs and cisplatin could arise λrom a number oλ basic phenomena, includinμ the possibility oλ two or multiple event processes triμμered by the interaction oλ a sinμle keV electron with a GNP. Within nm oλ its location, a sinμle μold atom increases the density oλ LEEs by a larμe λactor [ , ], and hence, a GNP that contains thousands oλ μold atoms is expected to μenerate a dramatic increase in this density [ ]. Combined with the λact that cisplatin considerably lowers the enerμy threshold λor DS” λormation, a sinμle or multiple LEE interactions on opposite strands within a distance oλ base pairs could increase considerably the number oλ DS”s λormed in GNP–cisplatin–DN“ complexes.

Figure . Enhancement λactors EFs λor the λormation oλ SS”, DS”, and loss oλ supercoiled DN“ induced by keV electrons, obtained with GNP–DN“ complexes oλ ratio . The μroups oλ three histoμrams represent the respective damaμes. In each μroup, the EF corresponds to the damaμe when the GNP alone is bound to DN“ or when the GNP has been coated with liμands . and nm in lenμths correspondinμ to GNP@C H or GNP@DTDTP“ i.e., dithiolat‐ ed diethylenetriaminepentaacetic acid , respectively in the λiμure.

“s shown by Zhenμ et al., only one GNP per DN“ molecule is on averaμe necessary to increase DN“ damaμe considerably [ ]. Thus, as lonμ as the nanoparticles reach the DN“ oλ cancer cells, the amount to be administered to patients to obtain siμniλicant radiosensitization should be at most the same as that oλ the Pt‐druμs routinely administered in chemotherapy [ , ]. In recent in vitro experiments, GNPs were tarμeted to the DN“ in the cell nucleus by linkinμ peptides to the μold surλace [ , ]. Such vectored GNPs, tarμetinμ the DN“ oλ cancer cells, should be applicable in the clinic and may accordinμly oλλer a new approach to radiotherapy treatments. However, this type oλ radiotherapy is expected to be limited to

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superλicial tumors, owinμ to the requirement λor that low‐enerμy < keV X‐rays be used to optimize LEE production and hence radiosensitization by the photoelectric eλλect. To treat deep tumors, a radioactive source may have to be encapsulated inside a μold nanoparticle i.e., in a μold nanocaμe [ ]. Furthermore, iλ DN“ speciλicity cannot be achieved in patients, suc‐ cessλul treatment may still be possible by intratumor injection oλ GNPs, as recently shown by Shi et al. [ ] and ”obyk et al. [ ].

. Summary and Conclusions The experimental and theoretical results oλ LEE impact on sinμle‐ and double‐stranded DN“, its basic constituents, protein subunits, as well as radiosensitizers and chemotherapeutic aμents alone or bound to DN“ were reviewed. Experimental details oλ LEE interactions with these biomolecules were obtained in both the condensed and μas phases. The condensed‐phase experiments were conducted in UHV and at atmospheric pressure under environments closer to those oλ the cell. From these studies, which provide a λundamental comprehension oλ the role oλ TM“s in irradiated bioloμical systems, we can arrive with considerable certainty at the λollowinμ conclusions on LEE‐induced damaμe to biomolecules. In the low‐enerμy ranμe i.e., below the threshold λor dipolar dissociation ~ eV , bond rupture in biomolecules occurs essentially via the λormation oλ TM“s that decay either via autoionization with the accompa‐ nied production oλ dissociative electronically excited states, or into the DE“ channel. The induced damaμe depends on a larμe number oλ λactors, includinμ electron enerμy, the environment and topoloμy oλ the molecule, and the electrostatic or chemical bindinμ oλ small radiosensitizinμ molecules. Such λactors inevitably modiλy the liλetime and decay channels oλ transient anions, which oλten increase the damaμe cross sections. Since secondary electrons oλ low enerμy possess a larμe portion oλ the enerμy deposited by hiμh‐enerμy radiation, any modiλication oλ how their enerμy deposits at crucial cellular sites is expected to have a stronμ radioprotective or radiosensitizinμ action. With DN“ beinμ the main tarμet in radiotherapy, parameters that aλλect LEE‐induced DN“ damaμe are necessarily oλ relevance to radiosensitivity, and the mechanisms involved must be well understood to control and modulate the bioloμical eλλects oλ ionizinμ radiation. Many oλ these mechanisms are now well established as seen λrom the experiments and theoretical treatments reviewed in this chapter. Moreover, it has been shown that applyinμ λundamental principles oλ action oλ LEEs to radiosensitizers or chemotherapeutic aμents can lead to new strateμies on how to improve radiotherapy outcomes. In particular, the role oλ LEEs in radiation damaμe was related to enhancement oλ the destruction oλ cancer cells by Pt‐ druμs and μold nanoparticles. LEEs were λound to play an important role in providinμ μuidelines in chemoradiation cancer treatment, as well as in the development oλ more eλλicient clinical protocols. Such applications point out the need λor multidisciplinary studies in this λield, where LEE–biomolecule interactions have become an area oλ intensive investiμation that encompasses many aspects oλ cancer therapy.

Transient Anions in Radiobiology and Radiotherapy: From Gaseous Biomolecules to Condensed Organic and Biomolecular Solids http://dx.doi.org/10.5772/63293

Acknowledgements The authors μrateλully express thanks λor helpλul comments oλ Dr. “ndrew D. ”ass and Dr. Darel J. Huntinμ. LS acknowledμes the λinancial support λrom Canadian Institute oλ Health Research CIHR, via MOP and and λrom Natural Sciences and Enμineerinμ Research Council oλ Canada NSERC . S.P. acknowledμes the λinancial support λrom the U.S. Department oλ Enerμy Oλλice oλ Science, Oλλice oλ ”asic Enerμy Sciences under award number DE‐FC ‐ ER . Abbreviations “

adenine

“FM

atomic λorce microscopy

“PPJ

atmospheric pressure plasma jet

C

cytosine

C

circular

CL

cross‐link

CRT

chemoradiation therapy

DD

dipolar dissociation

DE“

dissociative electron attachment

DN“

deoxyribonucleic acid

DS”

double‐strand break

EF

enhancement λactor

ESD

electron‐stimulated desorption

ESI

electrospray ionization

eV

electron volt

F–C

Franck–Condon

G

μuanine

GNP

μold nanoparticle

HPLC

hiμh‐perλormance liquid chromatoμraphy

ICD

intermolecular Coulombic decay

keV

kilo electron volt

Kr

krypton

L

linear

LEE

low‐enerμy electron

M“LDI

matrix‐assisted laser desorption ionization

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MDS”

multiple double‐strand break

MeV

meμa electron volt

ML

monolayer

nm

nanometer

ps

picosecond

Pt

platinum

S“M

selλ‐assembled monolayer

SC

supercoiled

SE

secondary electron

SERS

surλace‐enhanced Raman spectroscopy

SS”

sinμle‐strand break

T

thymine

TM“

transient molecular anion

U

uracil

UHV

ultrahiμh vacuum

UV

ultraviolet

VFR

vibrational Feshbach resonance

Author details Elahe “lizadeh *, Sylwia Ptasińska and Léon Sanche *“ddress all correspondence to ealizade@uoμuelph.ca Department oλ Chemistry and ”iochemistry, University oλ Guelph, Guelph, ON, Canada Radiation Laboratory and Department oλ Physics, University oλ Notre Dame, Notre Dame, IN, US“ Groupe en Sciences des Radiations, Département de Médecine Nucléaire et Radiobioloμie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, QC, Canada

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] Sevilla M. Research breakthrouμh DN“ strandedness controls halouracil radiosensi‐ tization. Radiat. Res. – . DOI . /epjd/e ‐ ‐

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] Zhenμ Y, Huntinμ DJ, “yotte P, Sanche L. Role oλ secondary low‐enerμy electrons in the concomitant chemoradiation therapy oλ cancer. Phys. Rev. Lett. . DOI . /PhysRevLett. .

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] Tannock IF. Treatment oλ cancer with radiation and druμs. J. Clin. Oncol. . DOI . /JCO. .

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] Prestwich RJ, Shaakespeare D, Waters S. The rationale λor and the current role oλ chemoradiotherapy. J. Radiother. Pract. – . DOI . /CND. b e

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] Rezaee M, “lizadeh E, Cloutier P, Huntinμ DJ, Sanche L. “ sinμle subexcitation‐enerμy electron can induce a double strand break in DN“ modiλied by platinum chemother‐ apeutic druμs. Chem. Med. Chem. – . DOI . /cmdc.

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] Rezaee M, Sanche L, Huntinμ DJ. Cisplatin enhances the λormation oλ DN“ sinμle and double strand breaks by hydrated electrons and hydroxyl radicals. Radiat. Res. – . DOI . /RR .

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] Rezaee M, Huntinμ DJ, Sanche L. New insiμhts into the mechanism underlyinμ the synerμistic action oλ ionizinμ radiation with platinum chemotherapeutic druμs the role oλ low‐enerμy electrons. Int. J. Radiat. Oncol. ”iol. Phys. – . DOI . / j.ijrobp. . .

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] ”ehmand ”, Waμner JR, Sanche L, Huntinμ DJ. Cisplatin intrastrand adducts sensitive DN“ to base by hydrated electrons. J. Phys. Chem. ”. – . DOI . /jp

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] ”ehmand ”, Waμner J. R, Huntinμ D, Mariμnier JL, Mostaλavi M, Sanche L. Rate constant oλ reaction between the GTG‐cisplatin complex and hydrated electrons. J. Phys. Chem. ”. – . DOI . /acs.jpcb. b

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] Luo X, Zhenμ Y, Sanche L. DN“ strand breaks and crosslinks induced by transient anions in the electron‐enerμy ranμe ‐ eV. J. Chem. Phys. . DOI . / .

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] ”ao Q, Chen Y, Zhenμ Y, Sanche L. Cisplatin radiosensitization oλ DN“ irradiated with ‐ eV electrons role oλ transient anions. J. Phys. Chem. C. – . DOI . /jp h

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] Tippayamontri T, Kotb R, Paquette ”, Sanche L. Optimal timinμ in concomitant chemoradiation therapy oλ colorectal tumors in nude mouse treated with Cisplatin and LipoplatinTM. “nticancer Res. – . DOI . / /

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] Tippayamontri T, Kotb R, Sanche L, Paquette ”. New therapeutic possibilities oλ combined treatment oλ radiotherapy with oxaliplatin and its liposomal λormulations Lipoxal™ in rectal cancer usinμ nude mouse xenoμraλt. “nticancer Res. – .

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] ”oulikas T, Vouμiouka M. Cisplatin and platinum druμs at the molecular level. Oncol. Rep. – . DOI . /or. . .

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] “ndre N, Schmieμel W. Chemoradiotherapy λor colorectal cancer. Gut. . DOI . /μut. .

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] Sicard‐Roselli C, ”run E, Gilles M, ”aldacchino G, Kelsey C, McQuaid H, Polin C, Wardlow N, Currell F. “ new mechanism λor hydroxyl radical production in irradiated nanoparticle solutions. Small . DOI . /smll. .

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] Coulter J“, Jain S, Forker J, McMahon SJ, Schettino G, Prise KM, Currell FJ, Hirst DG. Evaluation oλ cytotoxicity and radiation enhancement usinμ . nm μold particles

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potential application λor cancer therapy. Nanotechnoloμy. . / ‐ / / /

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] ”utterworth KT, Wyer J“, ”rennan‐Fournet M, Latimer CJ, Shah M”, Currell FJ, Hirst DG. Variation oλ strand break yield λor plasmid DN“ irradiated with hiμh‐Z metal nanoparticles. Radiat. Res. – . DOI . /RR .

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] Chanμ MY, Shiau “L, Chen YH, Chanμ CJ, Chen HH, Wu CL. Increased apoptotic potential and dose‐enhancinμ eλλect oλ μold nanoparticles in combination with sinμle‐ dose clinical electron beams on tumor‐bearinμ mice. Cancer Sci. – . DOI . /j. ‐ . . .x

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] Coulter J“, Hyland W”, Nicol J, Currell FJ. Radiosensitisinμ nanoparticles as novel cancer therapeutics––Pipe dream or realistic prospect? Clin. Oncol. – . DOI . /j.clon. . .

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] Hainλeld JF, Slatkin DN, Smilowitz HM. The use oλ μold nanoparticles to enhance radiotherapy in mice. Phys. Med. ”iol. N –N . DOI . / ‐ / / /N

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] Jain S, Coulter J“, Hounsell “R, ”utterworth KT, McMahon SJ, Hyland W”, Muir MF, Dickson GR, Prise KM, Currell FJ, O'Sullivan JM, Hirst DG. Cell‐speciλic radiosensiti‐ zation by μold nanoparticles at meμavoltaμe radiation enerμies. Int. J. Radiat. Oncol. ”iol. Phys. – . DOI . /j.ijrobp. . .

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] Chithrani ”D, Stewart J, “llen C, Jaλλray D“. Intracellular uptake, transport, and processinμ oλ nanostructures in cancer cells. Nanomed. Nanotechnol. ”iol. Med. – . DOI . /j.nano. . .

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] Chithrani D”. Nanoparticles λor improved therapeutics and imaμinμ in cancer therapy. Recent Patents Nanotechnol. – . DOI . /

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] Chithrani D”. Gold nanoparticles as radiation sensitizers in cancer therapy. Radiat. Res. – . DOI . /RR .

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] Liu CJ. Enhancement oλ cell radiation sensitivity by peμylated μold nanoparticles. Phys. Med. ”iol. – . DOI . / ‐ / / /

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] Hainλeld JF, Slatkin DN, Focella TM, Smilowitz HM. Gold nanoparticles a new X‐ray contrast aμent. ”r. J. Radiol. – . DOI . /bjr/

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] ”run E, Duchambon P, ”louquit Y, Keller G, Sanche L, Sicard-Roselli C. Gold nano‐ particles enhance the X-ray-induced deμradation oλ human centrin protein. Radiation Physics and Chemistry. – . DOI . /j.radphyschem. . .

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] Kanμ ”, Mackey M“, El‐Sayed M“. Nuclear tarμetinμ oλ μold nanoparticles in cancer cells induces DN“ damaμe, causinμ cytokinesis arrest and apoptosis. J. “m. Chem. Soc. – . DOI . /ja

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] Hébert E, Debouttière P‐J, Lepaμe M, Sanche L, Huntinμ DJ. Preλerential tumor accumulation oλ μold nanoparticles, visualized by maμnetic resonance imaμinμ

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] ”obyk L, Edouard M, Deman P, Vautrin M, Pernet‐Gallay K, Delaroche J, “dam JF, Estève F, Ravanat JL, Elleaume H. Photoactivation oλ μold nanoparticles λor μlioma treatment. Nanomedicine. – . DOI . /j.nano. . .

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] Hyun Cho S, Jones ”L, Krishnan S. The dosimetric λeasibility oλ μold nanoparticle‐aided radiation therapy GNRT via brachytherapy usinμ low‐enerμy μamma‐/x‐ray sources. Phys. Med. ”iol. – . DOI . / ‐ / / /

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] Lechtman E, Mashouλ S, Chattopadhyay N, Keller ”M, Lai P, Cai Z, Reilly RM, Piμnol JP. “ Monte Carlo‐based model oλ μold nanoparticle radiosensitization accountinμ λor increased radiobioloμical eλλectiveness. Phys. Med. ”iol. – . DOI . / ‐ / / /

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] McMahon SJ, Mendenhall, MH, Jain S, Currell F. Radiotherapy in the presence oλ contrast aμents a μeneral λiμure oλ merit and its application to μold nanoparticles. Phys. Med. ”iol. – . DOI . / ‐ / / /

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] McQuaid HN, Muir MF, Taμμart LE, McMahon SJ, Coulter J“, Hyland W”, Jain S, ”utterworth KT, Schettino G, Prise KM, Hirst DJ, ”otchway SW, Currell FJ. Imaμinμ and radiation eλλects oλ μold nanoparticles in tumour cells. Sci. Rep. . DOI . /srep

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] Cho S. Estimation oλ tumour dose enhancement due to μold nanoparticles durinμ typical radiation treatments a preliminary Monte Carlo study. Phys. Med. ”iol. N – . DOI . / ‐ / / /N

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] Rahman WN. Enhancement oλ radiation eλλects by μold nanoparticles λor superλicial radiation therapy. Nanomedicine. – . DOI . /j.nano. . .

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] Casta R, Champeaux J‐P, Moretto‐Capelle P, Sence M, Caλarelli P. Electron and photon emissions λrom μold nanoparticles irradiated by X‐ray photons. J. Nanoparticle Res. – . DOI . /s ‐ ‐ ‐

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] Casta R, Champeaux JP, Sence M, Moretto‐Capelle P, Caλarelli P. Comparison between μold nanoparticle and μold plane electron emissions a way to identiλy secondary electron emission. Phys. Med. ”iol. – . DOI . / ‐ / / /

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] Xiao F, Zhenμ Y, Cloutier P, He Y, Huntinμ DJ, Sanche L. On the role oλ low‐enerμy electrons in the radiosensitization oλ DN“ by μold nanoparticles. Nanotechnoloμy. . DOI . / ‐ / / /

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] Zhenμ Y, Huntinμ DJ, “yotte P, Sanche L. Radiosensitization oλ DN“ by μold nano‐ particles irradiated with hiμh‐enerμy electrons. Radiat. Res. . DOI . / RR .

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] Zhenμ Y, Sanche L. Gold nanoparticles enhance DN“ damaμe induced by anti‐cancer druμs and radiation. Radiat. Res. – . DOI . /RR . .

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] Zhenμ Y, Cloutier P, Huntinμ D. J, Sanche L. Radiosensitization by μold nanoparticles comparison oλ DN“ damaμe induced by low and hiμh‐enerμy electrons. J. ”iomed. Nanotechnol. – . DOI . /jbn. .

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] Yao X, Huanμ C, Chen X, Zhenμ Y, Sanche L. Chemical radiosensitivity oλ DN“ induced by μold nanoparticles. J. ”iomed. Nanotechnol. – . DOI . /jbn. .

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] Sanche L. Cancer treatment low‐enerμy electron therapy. Nat. Mater. . DOI . /nmat

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] Shi M, Thippayamontri T, Gendron L, Guérin ”, Paquette ”, Sanche L. Increased radiosensitivity oλ colorectal tumor with intra‐tumoral injection oλ low dose oλ μold nanoparticles. in press .

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Chapter 9

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation Jean Engohang-Ndong and Roberto M. Uribe Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62705

Abstract Microbioloμical analyses on municipal sewaμe sludμe sample treated in a pilot plant process utilizinμ an electron accelerator with a beam enerμy oλ MeV were conducted as a way to show the potential oλ this technoloμy to decontaminate sludμe containinμ % solids. ”acterial counts includinμ total heterotrophic bacterial, total coliλorm, and λecal coliλorm counts were perλormed on sewaμe sludμe samples pre- and postirradiation with the electron beam at doses ranμinμ between . and . kGy. “t each irradiation dose, bacterial and Ascaris ova counts and survival were measured in triplicate as colony λorminμ units CFUs per milliliter ml oλ sewaμe sludμe. Experimental results obtained revealed that a dose oλ . kGy is enouμh to reduce bacterial load to consider the treated sewaμe sludμe saλe λor both the environment and human accordinμ to the Environmental Protection “μency standards. However, a dose oλ . kGy was needed to reduce the concentration oλ Ascaris ova at levels deemed saλe λor land applications. This study also showed that electron beam treatment is less enerμy consuminμ with shorter processinμ times than conventional techniques used to decontaminate sludμe. Taken altoμether, these observations open new avenues λor larμe urban aμμlomerations to save money on sewaμe sludμe treatment. Keywords: Electron beam, Irradiation, Microorμanisms, Sewaμe sludμe, Decontami‐ nation

. Introduction Radiation processinμ has been used in biotechnoloμical applications λor more than years. The eλλect oλ radiation on pathoμenic microorμanisms was λirst initiated in by Ethicon Inc. a

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subsidiary oλ Johnson and Johnson toμether with Hiμh Voltaμe Enμineerinμ Corp. a manu‐ λacturer oλ accelerators in order to sterilize sinμle-use medical devices such as μloves, hypo‐ dermic needles, sutures, surμical drapes. Nowadays, it is worldwide used, not only λor medical devices, but also λor cosmetics. The exact mechanism by which radiation kills microorμan‐ isms is not very well understood, but it is certainly related to the damaμe caused by the radiation to the DN“ molecule oλ the microorμanisms. “lso it is μenerally accepted that the smaller the microorμanism the larμer the dose oλ radiation needed to kill it. So, the radiation dose needed to kill bacteria will be larμer than the dose needed to kill human cells, and it will be smaller than the dose needed to kill a virus. Sterilization is not the only area in which radiation can be used in biotechnoloμical applica‐ tions. Radiation is beinμ used to develop new implant materials which are biocompatible. “n example oλ this is the irradiation oλ water-soluble polymers in aqueous solutions, with or without the addition oλ another monomer which μives rise to a variety oλ cross-linked μels which can be used in the biomedical λield. Some oλ these hydroμels can be used to hydrate the skin oλ patients with severe burns. Radiation is also used in the area oλ λood preservation. Dependinμ on the dose used on a λood commodity, the radiation can either sterilize e.μ., in meat products , kill bacteria includinμ Salmonella and Streptococcus species, disinλest e.μ., in λruits and μrains , kill insects in adult, larvae, or pupae staμes, or delay maturation e.μ., in some λruits and veμetables by decomposinμ the enzymes responsible λor ripeninμ.

. Application of electron beam technology The commercial use oλ irradiation to disinλect sludμe started in when an industrial μamma ray λacility λrom Geiselbullach near Munich Germany used Co- and Cssources [ ]. The λacility used , Ci oλ Co- and , Ci oλ Csand treated up to m /day oλ sludμe. More recently, a new technoloμy usinμ electron beam accelerators was developed in Miami, Florida where a . MeV m“ accelerator with a throuμhput oλ m /day, and in ”razil where a . MeV . kW accelerator, with a maximum throuμhput oλ l/min were described [ ]. However, these two studies only addressed the enμineerinμ aspects oλ the λacilities and the possibilities to use electron beam irradiation λor environmental applications. The radiation eλλects on the bacterial load and removal oλ noxious chemical compounds have been perλormed mostly in small samples oλ sludμe irradiated under laboratory conditions and mainly address either only the microbioloμical or the chemical eλλect oλ radiation in a sample oλ sludμe [ – ]. Processinμ and disposal oλ wastewater sludμe are a critical problem worldwide [ ] thereλore, new technoloμies to solve this problem are constantly beinμ souμht. Sludμe is commonly used as a soil amendment and λertilizer but must be treated in order to remove various bacteria, toxic compounds, parasites, and viruses. Many researchers have shown that exposinμ sludμe to hiμh-enerμy radiation successλully removes all the bacteria and other orμanisms λrom the sludμe. Thus, the riμht dose oλ radiation will ensure proper sludμe

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

disinλection. It has been shown that even a small dose oλ radiation will remove . % oλ all bacteria in sludμe [ ]. In addition to disinλection, irradiation oλ sludμe oλten accelerates sedimentation and λiltration, which helps λacilitate removal oλ water λrom the sludμe. Even while chanμinμ the physical makeup oλ sludμe, this does not aλλect the ability oλ usinμ sludμe as a μood λertilizer. The μeneration oλ oλλensive odors λrom sewaμe sludμe is also a concern in the subsequent disposal and/or use oλ sludμe. Volatile sulλur-containinμ compounds carbon disulλide CS , dimethylsulλide [ CH S], dimethyldisulλide [ CH S ] and volatile carboxylic acids acetic acid, propanoic acid, butanoic acid have been identiλied as odor causinμ compounds in sewaμe sludμe [ ].

. Sludge irradiation dosimetry . . Dose mapping: experimental procedure Prior to the determination oλ the dose usinμ diλλerent accelerator parameters, the scanned beam on top oλ the sludμe delivery system needed to be mapped in order to veriλy that all the water cominμ throuμh the weir lenμth oλ the sludμe delivery system would be exposed to the electron beam. The delivery system consists oλ a stainless steel box cm . in lonμ with two compartments, one λor the incominμ sludμe and the other one to drain the irradiated sludμe. The sludμe is transλerred λrom one compartment to the other throuμh a weir located in the center oλ the box. Irradiation takes place at the top oλ the weir Figure .

Figure . Irradiation dispositive used to irradiate sludμe. a Overall view oλ the system, showinμ the accelerator scan‐ ner , the window blower , the electron beam shutter , the sludμe delivery system , and the pipes deliverinμ the sludμe to the system . b Simulation oλ the process usinμ tap water. Lower portion oλ the accelerator scanner, beam shutter, weir, and incominμ water. The depth oλ the sludμe layer at the top oλ the weir was about . – . cm. c sludμe sample adapted λrom [ ] .

To map the extent oλ the irradiation zone alonμ the weir, a CT“ λilm was taped to the top oλ the delivery system just underneath the scanner system oλ the accelerator and irradiated λor s usinμ the λollowinμ accelerator conditions E = MeV, I = m“, and S = %. “λter irradiation, the optical absorption at nm was measured alonμ the λilm usinμ a Genesys

233

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spectrophotometer λitted with a drivinμ mechanism to measure λilm strips. “erial™ soλtware determined the dose λrom the absorbance measurements. . . Dose mapping: results and discussion Figure shows a μraph oλ the dose alonμ the top surλace oλ the weir to treat the sludμe. The μraph shows two λeatures, the extent oλ the irradiation zone on top oλ the weir system and the dose uniλormity alonμ the weir. The μraph shows an eλλective irradiation lenμth oλ . cm which is shorter than the lenμth oλ the weir itselλ cm . In order to ensure that all sludμe λallinμ over the weir was irradiated, two pieces oλ aluminum tabs cm lonμ were λastened to each edμe oλ the weir usinμ C-clamps. These tabs shortened the eλλective weir by a total oλ cm and allowed λor all the sludμe λallinμ over the weir to be irradiated by the electron beam μiven the λact that the scanninμ anμle oλ the electron beam is . °. The μraph also μives inλormation about the uniλormity oλ the electron beam on top oλ the weir and shows that the dose at the two ends oλ the weir is about % lower than the dose in the idle section oλ the weir. However, this measurement was taken under static conditions, and in the case oλ water or sludμe, the liquid will not move on a laminar λlow λashion and miμht have been receivinμ an averaμe dose with variations oλ up to ± . % assuminμ that part oλ the liquid moved on the middle section and another part on the extreme end oλ the weir. So, then it is reasonable to assume that with the movement oλ the sludμe as well as with its mixinμ, this miμht be the maximum diλλerence in dose achieved by the sludμe.

Figure . Dose alonμ the sludμe delivery system. The measurements were taken usinμ cellulose triacetate λilm irradiat‐ ed with MeV electrons, m“ oλ current, s oλ exposure time and % scanninμ aperture [ ].

. . Dose measurements: experimental procedure The dose delivered to the sludμe was determined λrom temperature measurements made on the sludμe beλore and aλter irradiation, aλter calibration in terms oλ dose with alanine pellets

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

and λilms. The irradiation oλ alanine dosimeters produces λree radicals that become trapped inside the solid matrix oλ the dosimeter and can be measured by electron spin resonance ESR spectrometry. The trapped radicals are stable over lonμ periods oλ time, and their concentration can be directly related to the absorbed dose as determined λrom a calibration curve. For the experiments described in this chapter, a ”ruker eScan ESR spectrometer usinμ an insert FL to measure the alanine λilms and an insert PH to measure the alanine pellets were used to measure the λree radicals. In a λirst experiment, alanine pellets and alanine λilm strips were randomly selected and irradiated in order to make a calibration curve oλ the pellets. The pellets would be used to measure the dose in sludμe once they were calibrated with the alanine λilms. The alanine pellets were divided into ten μroups oλ λour and were placed in small plastic baμs . cm lonμ and . cm wide, and sealed with heat. The baμs with the pellets were placed on a piece oλ cardboard, one at a time, on top oλ one oλ the carts that would be conveyed throuμh the electron beam. On the side oλ the individual baμs, λour alanine λilm strips were placed, to measure the dose. The cardboard was irradiated in the cart conveyor system oλ the NEO ”eam λacility Dynamitron electron accelerator and irradiated usinμ the λollowinμ beam parameters MeV electron enerμy and % scanninμ anμle the dosimeters were movinμ under the beam at a constant speed oλ . cm/s, and the current chanμed to μive diλλerent dose values ranμinμ λrom to kGy, accordinμ to Table . Once all the dosimeters were irradiated, the alanine λilms were measured to determine the dose in each run, and with this inλormation and the measurement oλ the intensity oλ the ESR siμnal oλ the irradiated pellets, a calibration curve was constructed. Dose kGy

Beam current mA . . . . . . . . . .

Table . Electron beam current values needed to produce the selected doses λor alanine pellets runninμ under the beam at . cm/s.

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“ second experiment consisted in irradiatinμ a set oλ pellets in a pyrex bakinμ dish containinμ cold tap water at a depth oλ . cm / in . The purpose oλ this experiment was to simulate the accelerator conditions needed to irradiate the sludμe. Four vials per run were used, each containinμ three alanine pellets. These vials were placed into the bakinμ dish and λloated on top oλ the water. The electron beam parameters were set up such that the electron enerμy was MeV and λive runs were conducted underneath the electron beam. Each run had a constant speed oλ the samples equal to . cm/s and the λollowinμ beam currents . , . , . , . , and . m“. “λter irradiations, the dose λrom the ESR intensity oλ each alanine pellet usinμ the ”ruker eScan instrument was determined. The next experiment measured the dose λor a sample oλ water runninμ throuμh the delivery system to irradiate sludμe and to relate those measurements to the temperature oλ the water cominμ in and μoinμ out oλ the system as measured by a set oλ thermocouples installed near the sludμe delivery system in the inλluent and eλλluent pipes. Small sealed plastic baμs containinμ two alanine pellets were introduced into the system throuμh a Tee€ connection into the pipe where the water λlowed and sent them throuμh the irradiation zone. “t this point, μallons oλ water was beinμ recirculated throuμh the system at GPM. Two sets oλ λive runs were conducted. ”eam conditions λor each set were as λollows λor each run E = MeV, S = %, I = . , . , . , . , and . m“, respectively. “λter irradiation, the plastic baμs with the alanine pellets were collected in a catch basket that would separate the sealed baμs λrom the water. Some oλ the baμs leaked water when they passed throuμh the water pump that removed the irradiated water λrom the system. The baμs that did not show water leaks were used to measure the dose. Dose measurements were then related to the temperature meas‐ urements λrom the thermocouples. Finally, the dose in the sludμe was determined λrom the temperature measurements with the thermocouples, aλter correctinμ λor the dose measured by the alanine pellets.

. . Dose measurements: results and discussion “s mentioned earlier, the dose absorbed by the sludμe was determined λrom temperature measurements in the sludμe aλter a calibration with alanine pellets was perλormed. Figure shows the result oλ the dose calibration oλ the pellets when irradiated with alanine λilms in the cart conveyor system oλ the NEO ”eam λacility. “s stated in the experimental section, the pellets were calibrated usinμ alanine λilms calibrat‐ ed at Risø National Laboratory and then used to calibrate the in-house ”ruker eScan spec‐ trometer that measured the doses. “λter this, the calibrated pellets were used to determine the dose in the experimental setup to irradiate the sludμe with the electron accelerator usinμ diλλerent beam currents. Thus, the μraph in Figure shows the dose recorded by the pellets run throuμh the irradiation dispositive usinμ water at diλλerent beam currents oλ the electron accelerator.

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

Figure . Calibration curve λor the alanine pellets used to measure dose in this experiment. The dose was measured by alanine λilms and the response oλ the pellets as the ratio oλ the ESR intensity oλ the alanine to the internal marker oλ the pellet holder. The eScan instrument perλormed a trendline analysis on the experimental data obtaininμ a ° polynomial as the best λit to the experimental data with a standard error oλ . and an R = . .

Figure . Doses oλ electron beam irradiation in water. Doses were measured by alanine pellets as a λunction oλ the elec‐ tron beam current oλ the accelerator. Water was runninμ in the system at a rate oλ μpm, and the electron enerμy was . MeV [ ].

“t the same time, the increase in temperature oλ the water runninμ throuμh the sludμe delivery system at constant λlow rate oλ μpm and diλλerent beam currents was recorded and com‐ pared with the dose μiven by the alanine pellets. This relationship was later used to determine the dose absorbed by the sludμe when irradiated with the electron beam. The λlow rate durinμ the irradiation oλ the sludμe sample was μpm instead oλ the μpm oriμinally selected λor this experiment. In order to keep the doses within the interval selected λor this experiment, it was decided to run the experiment at a reduced level oλ electron beam

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currents to compensate λor this eλλect. The dose was determined then λrom temperature increase oλ the sludμe by measurinμ the temperatures at the input and exit ports oλ the irradiation setup. Table presents results oλ the temperature increments and dose measure‐ ments as a λunction oλ the beam currents λor the sludμe sample runninμ throuμh the delivery system. Beam current mA

Temperature increase °c

Dose kGy

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Table . Irradiation conditions used to achieve tarμeted doses. Sludμe samples were λlowinμ at a rate oλ

μpm [ ].

. Elimination of potential pathogenic bacteria in municipal sludge . . Sampling: experimental procedure Sample collection, transport, and storaμe are crucial when studyinμ the eλλect oλ electron beam irradiation on microbial population λound in municipal sewaμe sludμe. In these experiments, sewaμe sludμe samples were collected in two separate batches. First batch contains pretreated municipal sewaμe sludμe or inλluent samples, and a second batch is made oλ municipal sewaμe sludμe treated with electron beam irradiation or eλλluent samples. In the case reported here, since the sludμe was treated with diλλerent doses oλ electron beam irradiation, samples were collected prior to inλluent and aλter eλλluent irradiation oλ sludμe at each dose. Several ml inλluent and eλλluent samples oλ sewaμe sludμe were harvested in sterile-caped plastic vials λor bacterial count and survival. Each sample was then placed on ice immediately aλter collection and transported in an isotherm ice container a cooler λrom the electron beam irradiation λacility to the microbioloμy laboratory λor microbial analysis. For accurate obser‐ vation oλ the direct eλλect oλ electron beam irradiation on bacterial population, samples should be analyzed as soon as possible aλter treatment. . . Sample analysis using membrane filtration method: experimental procedure Each sample was thorouμhly mixed, and serial dilutions were perλormed in × phosphatebuλλered saline. Inλluent samples were diluted up to − , while eλλluent samples were diluted up to − . Diluted samples were λiltered usinμ disposable λilter λunnels. For λiltration, ml oλ the diluted sample was transλerred with a sterile pipette into the middle oλ a sterile mm diameter and . μm pore size μridded membrane λilter. “λter λiltration, the λilter was washed with three volumes oλ × phosphate-buλλered saline. The λilter was then removed and transλerred on a -mm diameter -padded Petri dish plate containinμ ml oλ culture medium

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

λor total heterotrophic bacterial TH” , total coliλorm TC , and λecal coliλorm FC counts. In order to perλorm TH” counts, mHPC Heterotrophic medium was used and λor TC counts, mEndo medium was used, while m-FC medium supplemented with Rosolic acid was used λor FC counts. Plates were placed in plastic baμs containinμ moistened paper towels and trans‐ λerred in an incubator. Heterotrophic plates were placed in an incubator λor h at ± . °C, and TC plates were incubated λor – h at ± . °C, while FC were incubated at . ± . °C. Known positive and neμative controls were used in order to veriλy accuracy oλ analytical procedures λor identiλication and counts oλ heterotrophic, TCs, and FCs. Thus, λor TC media, Escherichia coli and Enterobacter aerogenes were used as positive controls, while Staphylococcus aureus and Pseudomonas aeruginosa were used as neμative controls. The positive control λor the FC media was E. coli, and the neμative control was E. aerogenes. Prior to testinμ, test orμanisms were μrown in tryptone soy broth and incubated overniμht at °C. “λter μrowth, these cultures were treated accordinμ to the procedure used λor sewaμe sludμe samples. Only dilution plates with a density oλ – colonies were counted. FC colonies appeared as diλλerent shades oλ blue, while other non-FC colonies appeared as μray or cream-colored. ”acterial counts were perλormed in triplicate to veriλy the reproducibility oλ results λor total heterotrophic counts, TC counts, and FC counts. . . Results and discussion ”acterial counts beλore and aλter irradiation were perλormed with the electron beam at doses . , . , . , . , and . kGy. The counts were done speciλically λor TH”, TC, and FC. Figure shows the eλλect oλ electron beam irradiation on bacterial survival in municipal sewaμe sludμe aλter treatment. It appears that TH”, TC, and FC counts decreased in a dose-dependent manner. This decrease in bacterial population is directly associated with the ionizinμ eλλect oλ electron beam irradiation that damaμes bacterial DN“ and biomembranes, and the production oλ reactive oxyμen species which also damaμe cell components. “ similar observation was recently made by Cao and Wanμ [ ] when they treated municipal sludμe with electron beam irradiation. However, these authors did not count speciλic types oλ bacteria.

Figure . Eλλect oλ electron beam irradiation on bacterial survival in municipal sewaμe sludμe samples. a Survival oλ total heterotrophic bacteria, b survival oλ total coliλorms, and c survival oλ λecal coliλorms [ ].

Lookinμ more into details, it was shown that when irradiatinμ sludμe with electron beam, a dose oλ . kGy, . ± . % TH” survived the treatment, while only . ± . % oλ TC and . ± . % oλ FC survived at the same irradiation dose. “t a dose oλ . kGy, while ± %

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oλ TH” survived the treatment, only . ± . % and . ± . % oλ the initial populations oλ TC and FC survived, respectively. “t doses oλ . kGy and above, neither TC bacteria nor FC were detected. Nevertheless, at a . kGy irradiation dose, . ± . % oλ TH” λrom the initial population survived the treatment. “t a dose oλ . kGy and above, no siμniλicant TH” λrom the initial population were leλt in treated sewaμe sludμe samples [ ]. Table summarizes bacterial counts per μram oλ sludμe dry weiμht at diλλerent electron beam doses. From these results, D -values were determined as . , . , and . kGy λor TH”, TC, and FC respec‐ tively. D -values are deλined as doses necessary to kill % oλ the bacterial populations in the sample λor irradiation conditions applied, or the dose needed to reduce the bacterial popula‐ tion by a λactor oλ . “ close look at Table shows that dose . kGy reduces the FC counts to colony λorminμ unit CFU per μram oλ sludμe dry weiμht, a count that is within the Environmental Protection “μency EP“ norm to classiλy such treated municipal sewaμe sludμe as class “ sludμe utilizable λor land application in aμriculture [ ]. However, λrom the D -value determined λor FC, based on initial population oλ FC in inλluent samples, the dose required to convert this sludμe to class “ was estimated to be . kGy. “lthouμh no previous work similar to this one is known to perλorm a comparison with our estimated D -value, nevertheless, water-based and surλace membrane Bacillus spore killinμ D -values were reported to be . and . kGy, respectively [ , ]. These values are about twice lower than the . kGy determined in our case. This diλλerence could be attributed to the presence oλ a larμe amount oλ orμanic and inorμanic materials that make our sample relatively thick and sliμhtly viscous compared to water and a surλace membrane. Dose kGy

Sluge dry

Total

Total

weight gram

heterotrophic

coliforms

percent

bacteria

Fecal coliforms

Counts CFU per μram oλ dry weiμht .

.

%

. ×

. ×

. ×

.

.

%

. ×

. ×

. ×

.

.

%

. ×

. ×

. ×

.

%

. ×

.

.

. .

.

%

. ×

.

.

.

.

%

. ×

.

.

Table . ”acterial counts in sludμe samples at diλλerent irradiation doses [ ].

. Elimination of Ascaris ova in municipal sludge . . Sampling: experimental procedure Compared to bacterial analyses oλ inλluent and eλλluent sewaμe sludμe samples, Ascaris ova analyses required much larμer volumes oλ biosolids sewaμe sludμe . Thus, several l samples

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

oλ sludμe were collected in sterile μlass bottles. Some samples were obtained as inλluent samples, while others were obtained as eλλluent samples, transλerred on ice immediately aλter collection, and transported to the microbioloμy laboratory λor prompt Ascaris ova counts. . . Sample analysis: experimental procedure From each l sample, ml oλ well-mixed sludμe was transλerred in a blender, then ml oλ sterile water was added, and the mixture was blended λor min at hiμh speed. The blended mixture was transλerred to a -l tall beaker to which % × deterμent was added in order to reach ml λinal volume. The same procedure was repeated λor the second halλ the sludμe sample, and the homoμenized mixtures were combined and allowed to settle overniμht in a cold °C room or in a reλriμerator. “t this staμe, some λloatinμ materials may be observed thereλore, stirrinμ occasionally the mixture with a wooden applicator has shown to help settle the material. The supernatant was discarded by vacuum aspiratinμ it to riμht above the layer oλ biosolids. The settled sediments were then transλerred into a blender to which ml oλ sterile water, blended aμain λor min at hiμh speed, and transλerred to a beaker. The blender was rinsed, and % × deterμent was added to reach ml λinal volume. Samples were allowed to settle λor h at °C aλter which the supernatant was discarded by vacuum aspiratinμ it to riμht above the layer oλ biosolids. The biosolids were resuspended into ml oλ % × deterμent and stirred λor min usinμ a maμnetic stirrer. Homoμenized sample was then strained throuμh a mesh μm sieve placed in a λunnel over a beaker. Samples were washed throuμh the sieve with a spray oλ % × deterμent λrom a spray bottle. The sample volume in the beaker was adjusted to ml by addinμ the necessary amount oλ % × deterμent and allowed to settle λor h at °C. The supernatant was discarded usinμ a vacuum, while the sediments were mixed and equally distributed in -ml centriλuμe sterile tubes. In each tube, the sample volumes were adjusted to ml with sterile water and centriλuμed λor min at ×μ. The supernatant was then discarded, and the pellet biosolids that should not exceed ml was resuspend in ml oλ MμSO speciλic μravity . . Each tube was vortexed λor min, and more MμSO was added to each tube to reach a volume oλ ml. The tubes were then centriλuμed λor min at ×μ. The top – ml oλ supernatant oλ each tube was poured throuμh a mesh μm sieve supported in a λunnel over a beaker. ”iosolids retained on the sieve were washed, rinsed, and collected into a ml beaker. The suspension oλ biosolids was then transλerred into ml centriλuμe tubes. Tubes were centriλuμed λor min at ×μ, and supernatants were discarded. Iλ the previous step μenerated more than one tube λor one initial sample, the sediments should be transλerred into one sinμle ml tube and the centri‐ λuμation step repeated. Finally, aλter discardinμ the supernatant, the biosolids were resus‐ pended in ml . N H SO . The vials were incubated at °C λor weeks. “λter days oλ incubation, when the majority oλ the controls were λully embryonated, samples were ready to be examined microscopically × usinμ a Sedμwick Raλter cell to enumerate the detected ova. Ova were classiλied as either nonviable unembryonated or viable embryonated to the λirst, second, or third larval staμe, those with the potential to become adult Ascaris . The percent moisture oλ the sample was determined by analyzinμ a separate portion oλ the sample, so that the λinal calculation oλ ova per μram dry weiμht could be determined. This was done by measurinμ the weiμht oλ the sludμe samples beλore and aλter incubatinμ at °C λor days,

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until dry by observation. Cateμories oλ ova per λollowinμ manner

μrams per weiμht were calculated in the

Ova/μ dry wt = NO × CV × FV / SP × TS where NO = no ova, CV = chamber volume = ml , FV = λinal volume in ml, SP = sample processed in ml or μ, TS = % total solids. . . Results and discussion In order to determine Ascaris ova viability per λour μrams oλ sludμe dry weiμht, the averaμe dry weiμht oλ untreated sewaμe sludμe samples was λirst determined. Hence, the dry weiμht oλ untreated sewaμe sludμe samples was ± % total solids. On averaμe, untreated sewaμe sludμe contained ± Ascaris ova per λour μrams oλ dry weiμht. Figure shows percentaμes oλ Ascaris ova viability aλter treatment oλ sewaμe sludμe samples with electron-beam doses oλ . , . , . , and . kGy.

Figure . Eλλect oλ electron beam irradiation on Ascaris ova survival in municipal sewaμe sludμe. Percentaμes oλ Ascaris ova survival aλter irradiation oλ samples [ ].

Similar to bacterial counts, the results indicate that the viability oλ Ascaris ova decreases in a dose-dependent manner [ ] with a D -value oλ . kGy. “t dose . kGy, ± % ± Ascaris ova per λour μrams oλ dry weiμht oλ viable ova survived the treatment, while only ± . % ± Ascaris ova per λour μrams oλ dry weiμht ova survived at dose . kGy. “t dose . kGy, the survival rate dropped to ± . % ± Ascaris ova per λour μrams oλ dry weiμht . No Ascaris ova were detected in sewaμe sludμe samples irradiated at . kGy. However λrom

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

our counts, we estimated the electron-beam dose . kGy to be necessary to obtain a sewaμe sludμe containinμ less than one Ascaris ova per λour μrams oλ sludμe dry weiμht, meaninμ that the dose oλ . kGy applied durinμ our experiments was hiμh enouμh to achieve a class “ sludμe. Indeed, accordinμ to EP“ standards, to be considered class “, sewaμe sludμe must contain less than one Ascaris ovum per λour μrams oλ sludμe dry weiμht [ ].

. Economic benefits of using electron beam irradiation for the treatment of municipal sewage sludge “n important aspect in the implementation oλ a new technoloμy such as an electron accelerator in a wastewater treatment plant is to anticipate its impact on the operation costs oλ the λacility and on the environment. In a recent investiμation, the number oλ kWh used durinμ the irradiation process oλ the sewaμe sludμe was considered. Data were obtained λrom the electrical supply company deliverinμ power to the NEO ”eam accelerator λacility Toledo Edison, Toledo, Ohio on the day oλ the experiment. Enerμy consumed by the electron accelerator recorded in Figure shows a relatively stable plateau in the power consumed at the λacility prior to sample irradiation. The dosimetry calibration oλ the irradiation setup started at am with an increase oλ the beam current λrom to . m“ in equal time intervals. From am until the end oλ the irradiation procedure, we observed a constant increase in power consumption. However, the μraph only shows electricity consumption λrom am until am.

Figure . “veraμe power consumed at the NEO ”eam electron λacility on the day oλ the experiment inλormation pro‐ vided by Toledo Edison, Ohio, US“ [ ].

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The power consumed at a speciλic irradiation dose was obtained in terms oλ the beam current used, and the cost was determined to be $ . /kWh. Thereλore, at irradiation doses . and . kGy, the costs were $ . and $ . per m oλ sludμe, respectively. This represents only % oλ increase oλ the cost when quadruplinμ the dose oλ irradiation to achieve the required Ascaris ova reduction to a class “ biosolids, suμμestinμ that when selectinμ a hiμher dose oλ irradiation oλ sludμe, the increase in cost due to the use oλ hiμher beam currents should not be a concern [ ]. Similar results were obtained by other authors who estimated the cost oλ usinμ electron beam and μamma radiation λor the disinλection oλ sludμe. However, experiments developed were perλormed under diλλerent considerations. Indeed, a team in Florida reported a cost oλ $ . per μallons oλ sludμe λor a . MeV electron irradiation λacility runninμ at μallons per minute, while another μroup compared μamma and electron beam irradiations λor a sample oλ activated sludμe and obtained treatment costs oλ $ . /m λor μamma irradiation and $ . /m λor electron beam irradiation, which are lower compared with $ . –$ . when usinμ conventional technoloμy at the Central District Wastewater Treatment Facility in Miami Dade County [ ]. Furthermore, a comparison was made between irradiation at dose kGy and incineration oλ sludμe samples and showed a cost oλ $ . /m λor this latter compared with $ . /m when usinμ μamma radiation. In both instances, μamma and electron beam irradiations prove to be more economic than incineration [ ]. Taken altoμether, these observations show that electron beam irradiation oλ sludμe is less enerμy consuminμ, with shorter processinμ times, and a more environmental λriendly technoloμy compared to methods such as incineration.

. Conclusion Electron beam irradiation technoloμy is able to decrease microbial populations in a dosedependent manner. In the experiments described in this chapter, it has been estimated that . kGy oλ irradiation is suλλicient to reduce bacterial populations to saλe levels λor aμricultural use. However, a dose oλ . kGy is required to eliminate risks oλ inλection by helminths. “ltoμether, these observations suμμest that irradiation oλ municipal sludμe with electron beam requires at least a dose oλ . kGy to eliminate risks oλ microbial inλection. Furthermore, electron beam technoloμy is more cost-eλλective and less time-consuminμ than incineration in order to achieve a class “ sludμe accordinμ to EP“ standards.

Author details Jean Enμohanμ-Ndonμ * and Roberto M. Uribe *“ddress all correspondence to jenμ[email protected] Kent State University at Tuscarawas,, New Philadelphia, Ohio, US“ Kent State University, Kent, Ohio, US“

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705

References [ ] Lessel T. and Suess “., Ten year experience in operation of a sewage sludge treatment plant using gamma irradiation. Radiation Physics and Chemistry , . pp. – . doi . / / [ ] ”orrely S.I., et al., Radiation processing of sewage and sludge. A review. Proμress in Nuclear Enerμy, . – pp. – . doi . /S [ ] Reinthaler F.F., et al., Resistance patterns of Escherichia coli isolated from sewage sludge in comparison with those isolated from human patients in 2000 and 2009. Journal oλ Water and Health, . pp. – . doi . /wh. . [ ] Younμ S., Juhl “., and O'Mullan G.D., Antibiotic-resistant bacteria in the Hudson River Estuary linked to wet weather sewage contamination. Journal oλ Water and Health, . pp. – . doi . /wh. . [ ] Zhou ”.W., et al., Effect of microwave irradiation on cellular disintegration of Gram positive and negative cells. “pplied Microbioloμy and ”iotechnoloμy, . pp. – . doi . /s [ ] Pikaev “.K. and WoodsR.J., ed. Applied Radiation Chemistry: Radiation Processing. New York, United States oλ “merica, , Wiley. pp. . [ ] Enμohanμ-Ndonμ J., et al., Effect of electron beam irradiation on bacterial and Ascaris ova loads and volatile organic compounds in municipal sewage sludge. Radiation Physics and Chemistry, . pp. – . doi . /j.radphyschem. . . [ ] Cao C. and Wanμ M., Treatment of municipal sludge by electron beam irradiation. Nuclear Science and Techniques, . pp. – . doi . /j. /nst. . [ ] US EP“. 0 CFR Part 50 —Standards for the Use or Disposal of Sewage Sludge. Environmental Protection “μency. Washinμton, D.C.

.

[

] Fiester S.E., et al., Electron beam irradiation dose dependently damages the bacillus spore coat and spore membrane. International Journal oλ Microbioloμy, . p. . doi . / /

[

] Helλinstine S.L., et al., Inactivation of Bacillus endospores in envelopes by electron beam irradiation. “pplied and Environmental Microbioloμy, . pp. – . doi . /“EM. . . .

[

] Meeroλλ D., et al., Radiation-assisted process enhancement in wastewater treatment. Journal oλ Environmental Enμineerinμ, . pp. – . doi . / “SCE -

[

] Swinwood J.F. and Kotler J., Sewage sludge pasteurization by gamma radiation: Financial viability case studies. Radiation Physics and Chemistry, . – pp. – . doi . / -

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Chapter 10

Radiation Effects in Polyamides Mária Porubská Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62464

Abstract Polyamides P“s are larμely used either as enμineerinμ materials in virμin λorm or as composites and a component oλ polymer blends. Various processes have been used to modiλy some properties oλ polymers to improve their utility. For this purpose, radiation technoloμies present clear, one-step procedures and oλλer improvement to the perλormance oλ P“ materials. Irradiation by accelerated electron beams, γ-rays, and accelerated protons is applied on P“s, particularly P“- , as well as P“ composites. Variations oλ important characteristics, such as chemical structure, supermolecular structure, mechanical properties, thermal resistance, water absorption, and other parameters, are analyzed involvinμ results obtained by other authors. The application oλ irradiation on incompatible polymer blends involvinμ P“ is presented as well. The selection oλ radiation treatment oλ P“s has to be considered to obtain optimal results. Keywords: Polyamide, Properties, Electron beam, γ-rays, Proton beam

. Introduction Polyamides P“s are linear semicrystalline polymers containinμ amide μroups -CO-NH- in the chains. The nomenclature applied λor P“ uses numbers to describe the number oλ carbons between acid and amine λunction μroups includinμ the carbon oλ the carboxylic acid. Two types oλ polyreactions are used λor their preparation. The λirst, polyaddition, is based on a lactam as the startinμ reactant. “λter openinμ the lactam rinμ breakinμ peptide bond, the created end μroups -C O - and -N H - are coupled with -N H - and -C O - μroups oriμinatinμ λrom other cleaved molecules oλ the lactam. This is the case oλ P“- when ε-caprolactam is used.

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Radiation Effects in Materials

n [ (CH 2 )5 - CO - N H ] ® éë -HN - ( CH 2 )5 - CO - ùû H2 O

n

The same result can be reached usinμ the correspondinμ amino acid. However, the cleavaμe oλ water molecules is required, which is the characteristic λor a polycondensation mechanism. Thereλore, polycondensation is the second polyreaction used to prepare P“s. The most commonly applied reaction is the polycondensation oλ dicarboxylic acids with diamines e.μ., adipic acid with hexamethylene diamine μivinμ P“- . H 2 N - (CH 2 )6 - NH 2 + HOOC - (CH 2 ) 4 - COOH ® [-HN - (CH 2 )6 - NH - OC - (CH 2 ) 4 - CO -]n

In such a case, the structure oλ the P“ corresponds to the repetition oλ structure unit consistinμ oλ one oλ each monomer, so that they alternate in the chain unlike λor a P“ chain synthesized λrom a monomer as sinμle startinμ reactant. Many demandinμ applications require a careλul control oλ the synthesis as well as processinμ conditions considerinμ the resultinμ molecular mass. Variation oλ the startinμ reactants enables a larμe scale oλ P“s diλλerinμ in properties λrom hard and touμh P“ to soλt and λlexible to be acquired. Dependinμ on the type, P“s absorb diλλerent amounts oλ moisture, which aλλect the mechanical as well as dimensional characteristics. In μeneral, P“s are characterized by hiμh riμidity, hardness, abrasion resistance, thermal stability, μood slidinμ properties, stress crackinμ resistance, barrier properties aμainst oxyμen, smells, and oils. The disadvantaμes oλ P“ types involve a weak stability in the presence oλ UV radiation, oxidizinμ aμents, stronμ acids, and bases, hiμh shrinkaμe in molten section, deμra‐ dation in electrical and mechanical properties due to hiμh moisture absorptivity, and hiμh notch sensitivity. The various particular properties oλ P“s enable various P“s to be processed into various items. They are most λrequently used in the textile industry, electrotechnics, and automotive industry as enμineerinμ plastics either virμin or composites with modiλyinμ λillers. Dependinμ on the type oλ the product application, the manuλacturers can adjust the properties oλ initial materials to some extent. ”esides physical modiλication, involvinμ admixture oλ proper additives, the chemical modiλication oλ P“ can also be applied. “ccordinμ to P“ type, a hiμh meltinμ temperature within °C up to °C occurs. Thereλore, the homoμenous admixture oλ intended aμents into the melt is possible only λor suλλiciently thermally stable substances. When the chemical modiλication oλ P“ requires the μeneration oλ radicals e.μ., μraλtinμ various λunctional μroups or crosslinkinμ initiated by orμanic peroxides , then this modiλication cannot be always carried out in melt due to a weak thermal stability oλ some substances participatinμ in the process. In particular, peroxides will be thermally destroyed well beλore the P“ is melted. This handicap can be overcome usinμ a proper radiation technoloμy enablinμ such a modiλyinμ process in the solid state. Presentinμ a technoloμy oλ one step, the radiation technoloμies have been larμely applied durinμ the last decades and have brouμht a wider spectrum oλ properties or desiμn variations.

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

”ecause P“- and P“- comprise most oλ the world’s market ~ % [ ], the eλλects oλ radiation modiλication involvinμ them have been λrequently investiμated. Concerninμ some conλlictinμ reports on electron beam eλλect on polymers λound in scientiλic sources, in μeneral, it could be said that variations in μel content in P“s irradiated with identical doses may not be the same. The reason is that the competinμ reactions, chain scission and recombination, can be aλλected by several λactors, amonμ others polymer type with its molecular characteristics. However, under irradiation, the most decisive λactors are time and dose rate. The presence oλ oxyμen provokes some side reactions and the consequence is a complex process. The oxyμen eλλect can be hardly eliminated completely even iλ the irradiation is carried out in an inert atmosphere. Within the simultaneous process oλ recombination and scission macroradicals, the most important λactor is the stationary concentration oλ the macroradicals. Thereλore, althouμh the doses are the same, the results may diλλer iλ diλλerent electron beam sources and P“ types are used. From this aspect, every comparison can be oλ λraminμ character only. The same can be said reμardinμ γ or proton exposure.

. Electron beam irradiation of PAs The eλλect oλ electron beam on P“s depends on several λactors, such as installed parameters oλ the accelerator, absorbed dose, rate oλ the dose, environment oλ irradiation, μeometry oλ irradiated object, temperature, and postradiation treatment. Concerninμ the environment, air is used mostly and an inert atmosphere is less common but more thriλty towards the polymer. Under irradiation oλ polymers, λree radicals are created. Subsequently, two main actions take place, that is, recombination oλ the radicals resultinμ in crosslinkinμ and oxidation resultinμ in polymer deμradation. ”oth processes run in parallel [ ], competinμ mutually, and the results depend on concrete conditions. What exactly occurs when a P“ is irradiated with an electron beam? “n interaction occurs primarily in hydrocarbon sequences R . The complete action involves three basic steps initiation μeneration oλ λree radicals , propaμation, and termination. In μeneral, the λollowinμ scheme can describe such processes. Initiation R Î R * ® R ° + H° Propaμation R ° + O 2 ® ROOo ROOo + RH ® R ° + ROOH

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Radiation Effects in Materials

D

ROOH ® ROo + HOo D

ROOR ® 2ROo

The μenerated radicals can take part in the destruction oλ the next hydrocarbon sequences, and hydroperoxides start the λormation oλ new radicals and intermediates. In the presence oλ oxyμen, the creation oλ carbonyl and aldehyde μroups is siμniλicant as well. Termination ROOo + H o ® ROOH ROOo + R o ® ROOR In the case oλ P“- , the splittinμ oλ H λrom ethylene μroup occurs most probably in the vicinity oλ the –NH–CO– sequence - NH - éëCO - ( CH 2 )4 - CH 2 - NH ùû - Î - NH - éëCO - ( CH 2 )4 - C° H - NH ùû - + H ° n

n

However, abstraction oλ hydroμen can occur in any other place within the hydrocarbon sequence as well. Propaμation takes place accordinμ to the above-mentioned steps. Termination oλ the radicals can occur as λollows a Crosslinkinμ 2 - NH - [CO - (CH 2 ) 4 - C° H - NH]n - ® - NH - [CO - (CH 2 ) 4 - CH - NH]n | - NH - [CO - (CH 2 ) 4 - CH - NH]n b Disproportionation 2 - NH - [CO - (CH 2 ) 4 - C° H - NH]n - ®

® NH - [CO - (CH 2 )5 - NH]x - + - NH - [CO - (CH 2 ) 4 - CH = N]n - x c Oxidation and λollowinμ deμradation

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

1 - NH - [CO - (CH 2 ) 4 - C° H - NH]n - + O 2 ® - NH - [CO - (CH 2 ) 4 - CH ( Oo ) - NH]n 2 - NH - [CO - (CH 2 ) 4 - CH(O° ) - NH]n - +H o ®

® - NH - [CO - (CH 2 ) 4 - CH=O]y +NH 2 - [CO - (CH 2 )5 - NH -](n-y)

”esides the above-mentioned irradiation conditions, the λormation oλ intermediates and λinal products can be aλλected by the polymer structure, so that the products can be variable because oλ some side reactions. . . Variations in chemical structure In μeneral, the modiλication oλ semicrystalline polymers by enerμetic radiation in the solid phase below the meltinμ temperature oλ the crystallites is characterized by chanμes proceedinμ preλerentially or, in many cases, almost exclusively in the amorphous phase [ , ]. Within the pre-crosslinkinμ phase, there is the branchinμ in the polymer [ ] as revealed by the solution viscosity measurement λor P“- [ , ] and μlass λiber-reinλorced P“- P“- /GF with % GF [ ], indicatinμ an increase in the molecular weiμht due to the recombination oλ macroradicals at the polymer chain centers Figure . Consequently also, viscosity increases in normal cases.

Figure . Dependence oλ viscosity number λor virμin P“- and P“- in P“- /GF on electron beam absorbed dose. “dapted λrom Porubská et al. [ ].

“ measurable portion oλ insoluble μel occurs at approximately irradiation is conducted in air Figure .

kGy μel point when the

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Figure . Dependence oλ μel content on absorbed electron beam dose λor virμin P“- and P“- /GF With permission oλ Elsevier.

% composite [ ].

This μel point is conλirmed in several studies [ – ], althouμh a low μel content λor P“- was measured under the kGy dose as well [ , ]. Some speciλic results in experiments with electron beam irradiation oλ P“- and P“- , tyre cords and calendered λabrics are published by “ytaç et al. [ ] when, contrariwise, some decrease in limitinμ viscosity number with increasinμ dose was observed within doses oλ to kGy. The measured data are explained by suλλicient time λor oxyμen to diλλuse into the samples durinμ the λoreμoinμ calenderinμ as well as by a low dose rate Gy/pass . Under those conditions, radiolytic and oxidative deμradation occur. The λollowinμ strenμth testinμ conλirmed the objectivity oλ the results. Irradiation temperature

p /q

Gs

Gc

.

.

.

.

°C

.

.

.

.

°C

.

.

.

.

°C

.

.

.

.

RT

Gs/Gc

Table . Radiochemical Gs scission yield and Gc crosslinkinμ yield oλ P“- irradiated at diλλerent temperatures [ With permission oλ Elsevier.

].

”esides dose, temperature at the irradiation site also plays a role. “s study [ ] demonstrated that the crosslinkinμ eλλect μrows with increasinμ dose and temperature. Correspondinμ experiments with P“- λilm irradiated over a ranμe oλ to kGy and at a dose rate oλ . kGy/min were carried out at diλλerent temperatures λrom room temperature RT to °C involvinμ the μlass transition temperature Tμ oλ approximately °C. “lthouμh the P“- μel point λor all samples was observed more or less at kGy, the μel content increased with temperature and the hiμhest value % was observed λor a temperature oλ °C and dose oλ

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

kGy. The crosslinkinμ rates oλ P“- irradiated above Tμ are hiμher than those samples irradiated at temperatures below Tμ. The increasinμ tendency in crosslinkinμ with increasinμ temperature is attributed to the enhanced mobility oλ the P“- molecules above Tμ thereλore, the probability oλ radical recombination is hiμher. The radiochemical yields oλ crosslinkinμ and deμradation determined accordinμ to the Charlesby-Pinner equation [ ] are μiven in Table . The ratio p0/q0 [ ration oλ main chain λractures to chain units / units crosslinked to chain units ] λor P“- decreases with the increase in radiation temperature oλ the samples. This is a consequence oλ hiμher mobility oλ the chains and the recombination oλ radicals μenerated by the main chain scission as well as by the release oλ hydroμen radicals due to electron beam enerμy [Eq. ], indicatinμ that crosslinkinμ is the predominant process at temperatures above Tμ. In contrast, the scission prevails at RT, below Tμ [ , ]. Compared to the Gs/Gc values reported λor P“- , the scission dominates more in P“- than in P“- [ , , , ]. This demonstrates that a small diλλerence in P“ structure can play a role. The λinal amount oλ the μel in polymer is limited. Generally, in virμin P“, the μel portion μrows dramatically beyond the μel point and, in a certain phase, becomes stabilized. The reason is that a balance between the scission and recombination occurs, as the increasinμ viscosity in the matrix due to crosslinks breaks the mobility oλ the radicals to recombine. “lthouμh the μel content remains the same, the decrease oλ the swellinμ [ ] or molecular weiμht between crossbonds [ ] with increasinμ doses indicates that the network becomes denser [ ] as seen in Table . Dose kGy

RT

°C

°C

°C

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

Table . “veraμe molecular weiμht between crosslinks Mc in P“- samples irradiated at diλλerent temperatures and doses [ ]. With permission oλ Elsevier.

Irradiation experiments were also conducted in an inert nitroμen atmosphere and also with the annealinμ what led to lower chain scission and increased crosslinkinμ reaction [ ]. The crosslinkinμ aμents λor polymers, includinμ P“s, are molecules that contain two or more double bonds per molecule, such as triallyl cyanurate T“C , triallyl isocyanurate T“IC , and trimethylolpropane trimethacrylate TMPTM“ . The enerμy oλ electron beam easily cleaves them into radicals λormattinμ cross-bonds. Then, the crosslinkinμ aμent can increase the crosslinkinμ rate and shiλt the μel point to a much lower absorbed dose [ ] because oλ the hiμher eλλiciency oλ λree radical production. The presence oλ a λiller e.μ., GF reinλorcement in the P“ matrix can also modiλy the crosslinkinμ rate, even iλ contrarily [ ] in comparison to the

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crosslinkinμ aμents. The λiller increases the viscosity oλ the matrix, which leads to a retardation oλ the cross-bond λormation when compared to virμin P“ due to slower macroradical recom‐ bination, leavinμ more time λor disproportionation. Concerninμ μel λormation, the application oλ electron beam irradiation on incompatible polymeric blends or layers in laminates to μenerate λree radicals and the λollowinμ interaction, the μraλtinμ, between the components to improve their compatibility, can vary λrom case to case. Gel point shiλts dependinμ on the character oλ the polymeric components as well as possible crosslinkinμ aμent addition are shown in several works involvinμ P“- [ – ]. Rare data on electron beam eλλect on μel creation in P“- can be λound λor ethylene propylene diene monomer EPDM /P“- /maleated EPDM blend and these do not show any P“-in oriμin μel up to kGy [ ]. It is worth mentioninμ that crosslinkinμ becomes easier as the number oλ methylene μroups between the amide μroups increases [ , ]. This λindinμ is based on the μel measurement on P“- , P“, and P“- irradiated under the same conditions. This conclusion is under‐ standable because, as mentioned above, the initiation starts throuμh a hydrocarbon sequence. The lonμer the hydrocarbon sequence, the more probable the hydroμen abstraction occurs. . . Thermal properties related to supermolecular structure Diλλerential scanninμ calorimetry DSC is a useλul tool to examine the structural variations in irradiated polymeric materials. Two basic types oλ data can be obtained λrom DSC curves, meltinμ or crystallization temperature Tm or Tc and meltinμ or crystallization enthalpy ΔHm or ΔHc . The λormer is connected with the size oλ the crystalline units, whereas the last corresponds to the crystalline portion. The larμer the crystalline unit, the hiμher Tm observed. Similarly, the more the crystalline phase in the polymer, the hiμher the meltinμ enthalpy measured. In μeneral, λor most polymers λully or partially crosslinkable by electron beam irradiation, the dependences oλ both meltinμ temperature and meltinμ enthalpy on the dose measured λrom the λirst DSC heatinμ reλlect immediate chanμes in the oriμinal crystalline structure occurrinμ durinμ irradiation. The data λrom the second meltinμ demonstrates the overall chanμes particularly due to irradiation-induced crosslinkinμ and partial deμradation, both occurrinμ durinμ irradiation mainly in the amorphous phase. The oriμinal crystalline structure melts within λirst heatinμ. The λollowinμ coolinμ leads to the crystallization oλ the melt oλ the irradiated polymer, so that the eλλect is related to the overall deμree oλ crosslinkinμ, representinμ deλects hinderinμ the crystalline structure λormation aλter meltinμ durinμ the λirst heatinμ [ ]. The kinetic parameters oλ processes linked to the heat exchanμe can be determined as well. ”ecause P“s are semicrystalline polymers, DSC is used oλten to characterize them. “s mentioned previously, the crosslinkinμ mainly occurs in the amorphous phase. The eλλects oλ dose on the Tm determined λor virμin P“- in the λirst and second runs meltinμ Tm and remeltinμ Tm are displayed in Figure , whereas Figure shows the dependence oλ meltinμ and remeltinμ enthalpies. “ monotonous decrease in the Tm is observed over the to kGy dose ranμe and the second run Tm is lower than the λirst run Tm [ , ].

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

Figure . Variation oλ the λirst and second meltinμ temperatures with absorbed electron beam dose λor virμin P“- [ ]. With permission oλ Elsevier.

Figure . Variation oλ the λirst and second meltinμ enthalpy with absorbed electron beam dose λor virμin P“- [ ]. With permission oλ Elsevier.

Such behavior is typical λor the second run oλ irradiated crosslinkable polymers aλter meltinμ and λollowinμ the crystallization oλ a previously crosslinked material. The decrease oλ Tm points to the thinninμ oλ the lamellae as a consequence oλ crystalline phase disruption within irradiation. The decrease in ΔH indicates this λact, too. Consequently, it can be implicated that, durinμ irradiation also, a considerable deμradation occurs alonμ with crosslinkinμ. Similar λacts are observed, irradiatinμ P“- at temperatures above Tμ with doses oλ to kGy. Tm decreased λrom °C λor kGy up to °C λor kGy. However, irradiation at RT leads to a decrease oλ Tm up to kGy only with a subsequent mild increase [ ]. One possible explanation may be the λormation oλ larμer crystallites due to a hiμher μeneration oλ smaller λraμments λrom P“ chains at hiμher doses and those beinμ more mobile incorporate into existinμ crystallites more easy. This suμμestion is in compliance with the λindinμ that the samples irradiated above Tμ showed a predominance oλ the crosslinkinμ over scission Sec‐ tion . .

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The eλλect oλ irradiation on crystallinity is linked with the values oλ the meltinμ enthalpy directly proportionally, and some decrease is observed λor virμin P“- with risinμ dose Figure . The hiμher value oλ ΔHm than ΔHm λor P“- Figure is a consequence oλ diλλerent coolinμ rates between coolinμ the testinμ specimens aλter preparation by injection moldinμ usinμ a hiμher initial coolinμ rate λrom the processinμ temperature oλ ~ °C and coolinμ oλ the sample aλter λirst heatinμ in the DSC cell applied coolinμ rate oλ °C/min . Thereλore, a lower crystalline portion is the result λor rapidly cooled materials. The irradiation eλλect on P“- is also observable on the shape oλ the DSC meltinμ curves Figure .

Figure . DSC meltinμ endotherms oλ λirst meltinμ

–

°C λor P“- irradiated with electron beam.

The endotherms oλ irradiated samples become wider with increasinμ dose as a consequence oλ the proμressive lamella thinninμ and amorphization that took place under electron beam irradiation. “dditionally, the enlarμement in the peaks indicates that the distribution oλ crystallite size becomes broader while the unit endotherm surλace ΔHm decreases. P“- included in a multilayer λilm and irradiated in nitroμen applyinμ a dose in the ranμe oλ to kGy shows only a small total decrease in meltinμ temperature at approximately °C and the crystallinity is diminished λrom . % to . % [ ]. The inλluence oλ the crosslinkinμ aμent T“C on P“- irradiated with relatively low doses up to kGy demonstrates a more pronounced eλλect on Tm and crystallinity than present in virμin P“- . The decrease in both Tm and crystallinity λor the doped P“ is clearly observable already λor the kGy dose, whereas, λor the virμin P“- , the decrease is moderate, iλ any. The decrease in Tm seems to be dependent on T“C content the more T“C, the lower the Tm , but the measure oλ the decrease in crystallinity is not aλλected by T“C content in the ranμe oλ % to % [ ]. The development oλ thermal characteristics with dose can somewhat vary when P“ is part oλ a blend or composite. P“s are oλten used as reinλorced composites or λilled with various λillers,

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

with GF beinμ the most common reinλorcinμ additive. There is not much inλormation on the crosslinkinμ oλ reinλorced P“s P“/GF in the scientiλic literature. Concerninμ the chanμes in the meltinμ temperature Figure and enthalpy oλ P“- /GF Figure with risinμ dose, they are much less pronounced λor P“- /GF composite compared to virμin P“- Fiμures and , indicatinμ that the presence oλ GF partially eliminates the irradiation eλλects on P“. This conclusion arises λrom the dependences in Figure as well.

Figure . Variation oλ the λirst and second meltinμ temperatures with absorbed electron beam dose λor P“- /GF composite [ ]. With permission oλ Elsevier.

Figure . Variation oλ the λirst and second meltinμ enthalpy with absorbed electron beam dose λor P“- /GF posite [ ]. With permission oλ Elsevier.

%

% com‐

The examination oλ PP/P“- +talc composite with or without a compatibilizer or a crosslink‐ inμ aμent T“IC, applyinμ a dose in ranμe oλ to kGy [ ], reveals a decrease in Tm λor P“component only when doses and kGy are used. “ dose oλ kGy provokes already a minor Tm μrowth and that is evident λor the λormulation containinμ T“IC. However, all Tms are lower than the Tms λor the correspondinμ unexposed composite. Concerninμ the deμree oλ P“- crystallinity, the percentaμe λor PP/P“- +talc λormulation varies mildly beinμ lower λor the initial crystallinity λor the λormulation involvinμ the compatibilizer and T“IC, the decrease is deλinite.

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Radiation Effects in Materials

The behavior oλ P“- is similar to P“- in principle. Injection-molded P“- samples irradiated with and kGy doses show the decrease in initial Tm reμardless oλ the addition oλ T“C or the exposure at RT or °C. Nor does the water annealinμ aλλect this tendency, but the decrease λor the samples with no T“C irradiated at RT is a little less when compared to the others. The same can be said about the crystallinity [ ]. Thus, the dependences oλ the crystallinity on dose λor P“- λilms [ ] and λor the injection-molded pieces are the same essentially reμardless oλ the mode oλ sample preparation. Data on P“- meltinμ characteristics are λound λor EPDM/P“- /maleated EPDM blend aλter beinμ irradiated with to kGy doses [ ]. Meltinμ temperature does not show any chanμe and the crystallinity is more or less also the same. However, such a narrow dose ranμe does not allow the estimation oλ λurther development under hiμher doses. . . Mechanical properties The molecular and supermolecular structure oλ a polymer determines its properties. When any variation occurs in the structure, it should maniλest itselλ in some chanμes oλ the properties. Electron beam activates siμniλicant structural chanμes, namely, scission and crosslinkinμ as well as oxidative deμradation iλ irradiated in air. Each particular property oλ a polymer is unequally sensitive towards the structural modiλication thereλore, it is important λor exami‐ nation to be λocused exactly. Tensile properties, such as Younμ’s modulus, strenμth at yield or break, elonμation at yield or break, and λlexural and impact parameters, reλlect these variations well. In μeneral, when virμin P“ is irradiated, the development oλ the tensile parameters λollows the μeneral λramework that modulus and stress at yield are proμressive, whereas stress at break and elonμation are reμressive. The scale oλ measured values is a question oλ the quality oλ the irradiated P“. The shape oλ stress-strain curves λor the same P“ remains similar irrespective oλ the absorbed dose [ ]. The dimensional stability on load, the stiλλness, is one important parameter λor desiμn enμineers. In thermoplastics, the shape stability is aλλected by the crystallinity content to a μreat extent. Within the tensile properties, Younμ’s modulus is the correspondinμ testinμ parameter λor stiλλness. “s mentioned in Section . , electron beam irradiation in the solid state results in crosslink λormation primarily in the amorphous phase or at the crystal boundaries [ , ]. In addition, λor thermoplastics, an observable increase in the strenμth parameters occurs when the μel content is at or more than wt% [ ]. Thus, unless the crystalline phase is substantially deμraded, notable chanμes in the modulus will not occur as evident λrom the dependences oλ Younμ’s modulus λor virμin P“- and P“- /GF composite Figure . In reality, reμardinμ a larμe λluctuation in the standard deviation brouμht on by GF dispersion within the P“ matrix λor the composite, any variations oλ Younμ’s modulus are statistically nonsiμniλicant to be presented. Concerninμ virμin P“- , the increase in the modulus is evident at kGy dose when the μel content is more than %. In another study [ ], a steady increase in the modulus oλ virμin P“- is measured within the dose ranμe oλ to kGy. However, in this case, the μel point is measureable already at approximately kGy and % μrowth

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

Figure . Variation oλ Younμ’s modulus with absorbed electron beam dose λor virμin P“- and P“- /GF site [ ]. With permission oλ Elsevier.

% compo‐

in the μel content can be estimated at approximately kGy. The relative increase in the modulus at a kGy dose is approximately the same % over the initial rate as the abovementioned result. When the crosslinkinμ aμent is added to the polymer to increase the μel λormation, the limit oλ % μel is achieved earlier. Thereλore, the hiμher modulus is observed when compared to the virμin polymer [ ], as the crystalline phase, beinμ not yet impaired, is supported by the suλλicient μel portion. The modulus and yield tensile strenμth oλ injection-molded P“- irradiated in the ranμe oλ to kGy are λound to increase over the unexposed samples with dose but displays a maximum at kGy. Similar results are obtained in the elonμation development however, beyond kGy, the elonμation is reduced below the initial value [ ] due to crosslinkinμ. The inλluence oλ the crosslinkinμ aμent can also be demonstrated on tensile strenμth and elonμation oλ P“- exposed to irradiation within the ranμe oλ to kGy. These characteristics are kept the same [ ], because this dose ranμe does not involve the μel point yet. However, the addition oλ the crosslinkinμ aμent increases the tensile strenμth and a decrease in the elonμation immediately λrom kGy, indicatinμ that the correspondinμ μel point is lower than kGy in this case. The hiμher the crosslinkinμ aμent concentration, the μreater the eλλect is λound. The importance oλ the selection oλ the crosslinkinμ aμent is reλlected by the experiment where P“- is doped with % T“C, T“IC, or TMPTM“ when irradiated with doses up to kGy [ ] in air. The tensile strenμth λor virμin P“- and P“- with T“C exhibits a similar pattern oλ initial rise up to kGy λollowed by a μradual reduction up to kGy. In the case oλ P“ with TMPTM“, the tensile strenμth reduces continually. In the case oλ T“IC, in contrast, the strenμth rises throuμhout the whole ranμe oλ irradiation. The elonμation oλ P“- virμin as well as P“- with T“C or TMPTM“ reduces displayinμ a sharp decrease at kGy λor the P“ containinμ the aμents and a more moderate decrease λor virμin P“- up to kGy. ”eyond these doses, the correspondinμ values chanμe neμliμibly. The elonμation oλ P“- with T“IC λollows a completely diλλerent course. It μradually drops over the entire ranμe oλ dosaμe and the resultinμ elonμation is the hiμhest when compared to others Figure . This possibly

261

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Radiation Effects in Materials

indicates that, despite havinμ the hiμhest μel content, the network is less dense, with T“IC savinμ more elasticity compared to others.

Figure . Relative variation oλ elonμation oλ P“λrom Pramanik et al. [ ].

with and without crosslinkinμ aμents with dose oλ e-beam. “dapted

Concerninμ the modulus Figure , this increases beyond in compliance with the above-mentioned λindinμ that at least towards the modulus increase [ ].

Figure Relative variation oλ tensile modulus oλ P““dapted λrom Pramanik et al. [ ].

kGy sharply λor virμin P“% μel is needed to contribute

with and without crosslinkinμ aμents with dose oλ e-beam.

The addition oλ the crosslinkinμ aμents increases the modulus over the virμin P“- in the order oλ T“IC>T“C>TMPTM“, althouμh the dependences λollow individual courses. The crosslinkinμ eλλicacy oλ the aμents in P“- is oλ the same order as well. The eλλect oλ another aμent, μlycidyl methacrylate GM“ , is similar [ ]. P“- doped and then irradiated with a dose in the ranμe oλ to kGy in nitroμen to condensate mutually shows

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

a modulus at and kGy, which is % and %, respectively, above the unexposed virμin P“- . “t the same time, the correspondinμ tensile strenμth is determined to be approximately % over the virμin P“- . Radiation technoloμy is used in an eλλort to improve the deλicient compatibility oλ diλλerent polymers in blends or composites and to model the resultinμ properties to a certain extent due to the bindinμ oλ each other throuμh λree radicals μenerated in the components. P“- and linear low-density polyethylene LLDPE are typical immiscible polymers. The morpholoμic examination oλ the mixture oλ the P“- /LLDPE/GM“ exposed to electron beam under nitroμen atmosphere within the ranμe oλ to kGy displays a reduced diameter oλ the dispersion particles and an increase in the interλacial adhesion. The elonμation at break oλ the blend irradiated at kGy is approximately λour times hiμher than that oλ the virμin P“- . This parameter is stronμly reduced when the blend is irradiated at kGy, which is supposed to be the crosslinkinμ oλ LLDPE [ ]. The tensile strenμth and modulus increase with risinμ irradiation dose nonlinearly. Electron beam irradiation oλ multilayer λilm LDPE/P“- /LDPE with doses up to kGy in nitroμen results in the increase oλ the tensile strenμth and the decrease oλ the elonμation [ ].The μrowth is more rapid up to kGy and then is more moderate. In contrast, the elonμation decreases presentinμ a mirror curve to the strenμth. This phenomenon is explained by the λormation oλ carbonyl μroups in LDPE in the case oλ the low doses, which λacilitate the miscibility oλ the LDPE with P“- . On the contrary, at hiμh doses, the presence oλ crosslinked LDPE would most likely introduce microreμions oλ immiscibility with the P“- . The preparation oλ a thermoplastic elastomer λrom an immiscible blend consistinμ oλ the EPDM, maleated EPDM, and P“- is another demonstration oλ the utility oλ electron beam irradiation [ ]. The irradiation was conducted up to kGy in nitroμen so that P“- chain scission occurred μeneratinμ λree radicals but no crosslinkinμ and led to a mutual link oλ the components and λrom disastrous mechanical properties to desired ones. The increase is quoted λor Younμ’s modulus, tensile strenμth, and elonμation in addition, the recyclability oλ the thermoplastic elastomer is μained λor three cycles at least. Waste polymers can be used aμain when they are combined with other appropriate compo‐ nents. Thereλore, waste P“ copolymer P“- /P“- blended with acrylonitrile butadiene rubber and subjected to electron beam irradiation shows tensile strenμth and elonμation, dependinμ on dose and composition, at levels between the parameters oλ those individual components. The obtained compatibility matches with scanninμ electron microscopy SEM imaμes [ ]. “ composite consistinμ oλ ethylene-vinyl acetate copolymer EV“ λlame retarded by a combination oλ cellulose acetate butyrate microencapsulated ammonium polyphosphate, P“- , and T“IC reveals a drastic increase in tensile strenμth by % over the initial value at kGy. ”eyond this dose, the tensile strenμth λalls, whereas the elonμation at break decreases continually λrom the beμinninμ [ ]. “dhesive joints in composite items oλten involve P“s. Polycarbonate PC sheet covered with P“- beinμ irradiated with dose oλ to kGy [ ] displays variation in the λracture stress

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Radiation Effects in Materials

and elasticity oλ the joint as dependence on dose diλλerinμ λrom the neat components. Whereas the λracture stress λor the composite increases up to approximately kGy and levels beyond this, the strain λalls with risinμ dose up to kGy and then increases. Some optimum in the characteristics could be λound accordinμ to topical desiμn requirements. Younμ’s modulus oλ composite PP/P“- +talc with or without a compatibilizer or crosslinkinμ aμent T“IC, applyinμ a dose oλ to kGy [ ], μives the dependence on dose with compo‐ sition. Whereas the modulus oλ the mixture containinμ all components accounts λor only % PP/P“- +talc beλore irradiation, it exceeds the other mixtures aλter kGy irradiation. Qualitatively, the same tendency is observed λor tensile strenμth, too. These results indicate that, with a combination oλ suitable composition and electron irradiation, materials could be desiμned with the desired properties. Further research in this λield is open and not all eλλorts lead to desired results. For example, experiments with composites oλ monomer castinμ P“- containinμ % nanoλillers as particle carbon or silicon carbide or carbon shortcut λibers with no crosslinkinμ aμent μive only % increase in tensile strenμth and Younμ’s modulus when irradiated by electron beam with kGy dose [ ]. The weakness oλ P“s as semicrystalline materials is quantiλied λor a low impact strenμth or touμhness. “λter virμin P“- is electron irradiated, a considerable deterioration oλ these parameters is λound. The Izod impact strenμth λalls sharply with the risinμ dose, and aλter absorbinμ kGy, the impact strenμth retains % oλ the initial level only. The addition oλ the crosslinkinμ aμents chanμes this uniλormly decreasinμ behavior. “ccordinμ to the aμent type, the dependence oλ Izod impact strenμth on dose is oλ variable character, reachinμ a maximum at kGy λollowed by a sharp decline beyond this dose [ ]. However, the net result is a decrease when compared to the nonirradiated sample. “ rather diλλerent situation occurs λor P“- [ ]. The Izod impact strenμth oλ virμin P“- is reduced at kGy to % oλ the initial value and then displays a levelinμ eλλect up to kGy, and beyond this dose, a sharp decrease is λollowed by no siμniλicant chanμe at hiμher doses. “μain, the crosslinkinμ aμents have a variable inλluence and result in a dependence includinμ smaller λluctuations in comparison to the virμin P“- . “n observation oλ the λracture surλace leads to the λindinμ that both virμin and crosslinker-doped P“- irradiated up to kGy show ductile λailure, whereas the materials irradiated with doses oλ to kGy indicate brittle λailure. One oλ the several reasons why electron irradiation lowers the impact strenμth may be a certain obstruction in the dissipation oλ the impact enerμy when the initial amorphous phase is proμressively crosslinked and restricted in the chain motion and relaxation. The contribution oλ oxidative deμradation becomes more evident in the reduction at hiμher doses. The λlexural characteristics λor P“- reveal an analoμous behavior with the correspondinμ tensile strenμth and tensile modulus i.e., they increase with dose [ ]. The increase in the λlexural modulus at kGy is % over the initial level and the λlexural strenμth %, respectively. The addition oλ eλλective crosslinkinμ aμents T“IC and T“C raises these values. In the case oλ P“- , the λlexural modulus increases up to kGy by % and then it λalls sharply, remaininμ still at an increase oλ % over the initial level [ ]. The same crosslinkinμ

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

aμents as in the P“- increase the λlexural modulus, almost copyinμ the behavior oλ virμin P“- at a hiμher level. The irradiation oλ composite PP/P“- +talc with to kGy doses leads to an increase in λlexural strenμth by % when the composite contains also the compatibilizer and crosslinkinμ aμent T“IC, the increase is hiμher by %. ”oth correspondinμ λlexural moduli are increased by % and %, respectively [ ]. It can be concluded that, besides irradiation conditions, the mechanical properties in blends oλ P“ with other polymers or modiλiers are dependent on the character oλ all components and the interactions between them induced by the irradiation. . . Thermal resistance The thermal resistance oλ polymers is usually measured by heat deλlection temperature HDT and Vicat soλteninμ temperature. There are other speciλic tests adjusted to the λactual require‐ ments oλ manuλacturers. However, they are used by narrow μroups oλ desiμn enμineers and in the λramework oλ quality testinμ. The HDT or heat distortion temperature is the temperature at which a polymer sample deλorms under a speciλied load. It miμht be expected that parameter HDT will increase with risinμ dose. In λact, λor P“- irradiated within to kGy, it is λound that there is a proμressive μrowth up by °C at kGy. “ll the related values appear near °C, the Tμ oλ P“- [ ]. The HDT increase with increasinμ dose reλlects the proμressive restriction oλ the chain mobility in the amorphous phase as a consequence oλ the network structure λormation and the lower deλormability Figure .

Figure . Variation oλ HDT with absorbed electron beam dose λor virμin P“- and P“- /GF ed λrom Porubská et al. [ ].

% composite. “dapt‐

“ diλλerent situation is in GF-reinλorced P“- . The presence oλ GF restrains the seμmental motion oλ the polymer chains, and thereλore, the initial HDT °C observed λor the compo‐ siteP“- /GF is much hiμher than virμin P“°C . Unlike the virμin P“, the HDT values λor P“- /GF decreases in response to irradiation, with a decrease oλ °C at the hiμhest dose [ ]. “naloμous results can be assumed λor other composites as well.

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How much crosslinkinμ can aλλect HDT λor P“- is seen λrom the electron beam irradiation oλ P“- containinμ % T“C. Whereas the HDT beλore exposure is °C, aλter absorbinμ kGy dose, this λiμure increases up to °C [ ] due to ~ % μel content Figure .

Figure

. Variation oλ HDT with absorbed dose λor P“- at % T“C level. “dapted λrom Dadbin et al. [ ].

The irradiation oλ composite PP/P“- +talc in the ranμe oλ to kGy displays the rise in HDT dependinμ on the dose λrom °C λor the nonirradiated sample to °C λor that irradiated with kGy. However, when compatibilizer and crosslinkinμ aμent T“IC is incorporated in the composite, the HDT μives value oλ °C [ ]. The Vicat soλteninμ temperature or Vicat hardness is taken as the temperature at which the specimen is penetrated to a depth oλ mm by a λlat-ended needle with a mm cross-section. There is not much inλormation on the eλλect oλ electron irradiation on the Vicat soλteninμ temperature λor P“s in the scientiλic sources. Unlike the HDT, the Vicat temperature λor virμin P“°C reaches a maximum °C at the lowest dose oλ kGy and then decreases with increasinμ dose nearly returninμ to its oriμinal level °C [ ]. The mentioned increase is possibly related to the release oλ physical entanμlements due to the supplied enerμy λrom the electron radiation. That enables the involvement oλ some released seμments in amorphous phase into the crystalline phase and its enlarμement. “ moderate increase in the meltinμ enthalpy/crystallinity at kGy dose corresponds to this. The decrease in the Vicat temperature at a hiμher dose is assiμned to the proμressive disruption oλ the surλace structure and the thinninμ oλ the lamellae what is obvious also λrom the lower meltinμ onset Figure . The soλteninμ temperature λor P“- /GF composite is less pronounced, with a total decrease oλ only °C Figure . This observation corresponds to the diλλerent crystallinities oλ both materials P“- /GF > P“- . . . Water absorption Generally, P“s tend to absorb water due to the nonbindinμ interactions oλ water molecules with polar μroups in the matrix. The water present in P“ acts as a plasticizer. The water absorption aλλects the dimensional stability and mechanical properties oλ the polymers,

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whereas humidity in P“ matrix can support hydrolytic destruction and can also be a source oλ oxyμen when P“s are processed or irradiated acceleratinμ the polymer oxidative deμrada‐ tion. Thereλore, water absorptivity is one oλ the crucial parameters aλλectinμ the P“ properties. That is why the comparison oλ some characteristic values λor various P“s requires a standard conditioninμ temperature, humidity, and time beλore the P“ is tested. The entry oλ water molecules into a P“ matrix is controlled by diλλusion. The penetration oλ the matrix by water molecules requires enouμh space inside the matrix λor the translation motion oλ water molecules. The space is λormed by vacancies due to the rotatinμ movement oλ seμments oλ macromolecule chains. The λewer the restrictions oλ motion in the polymer seμments, the more vacancies are created. ”ecause the crosslinkinμ shortens the chain sequen‐ ces between the cross-points and thus restricts the seμmental rotation, water molecule mobility in the polymer should be more diλλicult suppressinμ water diλλusion. This supposition is conλirmed empirically. Water absorption in P“- irradiated in ranμe oλ to kGy decreases throuμhout all doses λrom . % to . % at the hiμhest dose [ ]. “s expected, the decline is μreater with the incorporation oλ the crosslinkinμ aμents T“IC or T“C Figure .

Figure . Variation oλ water absorption λor P“- without and with % crosslinkinμ aμents with dose oλ e-beam radia‐ tion [ ]. With permission oλ Elsevier.

”ecause the concentration oλ the eλλective crosslinkinμ aμent aλλects the μel content, it is expected to inλluence water absorption in the P“ correspondinμly. Such an example is shown in P“- doped with %, %, and % T“C [ ]. The measured data conλirmed this supposition and the larμest decrease at kGy is read λor P“- with %> %> % T“C. The decline oλ water absorption compared to virμin P“- irradiated within to kGy occurs also aλter addinμ approximately % GM“ under identical conditions [ ]. Similarly, injection-molded P“reveals a lowerinμ oλ water absorption when irradiated in the ranμe oλ to kGy, but the P“- dipped in T“C solution beλore the irradiation shows a λurther decrease in this parameter [ ].

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. γ-Irradiation of PAs In polymer chemistry, as λor electron irradiation, γ-irradiation is employed to initiate chemical reactions also in the solid phase without the addition oλ initiator. The purpose can be to initiate the crosslinkinμ oλ individual polymers or the μraλtinμ oλ various monomers onto P“ chains. ”asically with γ-irradiation oλ P“s, the same processes run as those with electron irradiation. However, some diλλerences occur due to variable conditions. . . Variations in chemical structure γ-Ray radiation diλλers λrom electron beam mainly by a much slower rate oλ dose due to γ-rays beinμ always oλ less enerμy than MeV. Thereλore, γ-irradiation requires a lonμer period to supply the same dose as an electron beam. When a polymer is γ-irradiated in air, enouμh time is available λor μenerated radicals to react with oxyμen. Thereλore, considerable oxidative deμradation can be expected alonμ with crosslinkinμ. In contrast, an inert atmosphere durinμ irradiation as well as aλter the irradiation suppresses oxidative deμradation and supports crosslinkinμ. However, the oxidative deμradation cannot be excluded absolutely due to some portion oλ oxyμen and possibly also humidity present in the polar P“ matrix. These antici‐ pations were conλirmed and both chain scission and crosslinkinμ are observed to occur in P“under γ-irradiation in either air or inert atmosphere, with chain scission prevailinμ over crosslinkinμ iλ irradiation proceeds in air [ ]. “ thorouμh comparison is provided by a recent study [ ] examininμ P“- and GF-reinλorced P“% GF irradiated with diλλerent γ-ray doses in the ranμe oλ to kGy in either air or inert atmosphere. “s displayed in Figure , it can be seen that the irradiation in air μenerates a small amount oλ μel in P“- only, whereas no μel is λound in the P“- /GF composite.

Figure . Dependence oλ μel content in P“- and P“- /GF composite on absorbed dose when γ-irradiated in air or inert atmosphere.

In the P“- , the crosslinked portion irradiated in air increases sliμhtly with the risinμ absorbed dose. Concerninμ the μel point, a calculation λollowinμ the Charlesby-Pinner equation [ ] usinμ the experimental data and takinμ into consideration the experimental errors μives an estimation that the μel point is to be in the vicinity oλ a dose oλ kGy λor the P“- irradiated in both atmospheres. Such μel point is somewhat hiμher compared to kGy dose value

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determined λor the same materials irradiated with electron beam in air [ ]. The irradiation oλ P“- in arμon atmosphere produced considerably more μel in comparison to exposure in air. It demonstrates oxyμen inλluence. The absence oλ oxyμen or low content oλ it aλλords better λacilities to λorm crosslinks λrom μenerated macroradicals because the macroradicals are not attacked. In arμon atmosphere, the μel point λor P“- as well as P“- /GF is observed to be approximately kGy. However, also in inert atmosphere, P“- shows more μel % than P“- /GF % λor the ultimate dose oλ kGy. The lower μel content in the composite conλirms the retardinμ action oλ the λiller on the networkinμ oλ the P“ matrix. Simultaneously measured solution viscosity λor P“- increases up to kGy, and above this dose, the viscosity could not already be measured correctly due to the incomplete dissolution oλ the P“- polymer indicatinμ incominμ μel point. The increase oλ the P“- solution viscosity below kGy indicates μrowth in the molecular mass via the recombination oλ the secondary macroradicals λormed on P“- chains, which leads to branchinμ as pre-crosslinkinμ staμe up to the μel point [ , ]. Whereas the irradiation oλ P“- /GF in air did not μenerate any μel within the applied dose, viscosity increased see Table , illustratinμ some recombination oλ the macroradicals and relatinμ μrowth in molecular mass. The solubility oλ the P“- /GF matrix was observed within all doses correspondinμ with no μel content. The reduction oλ the viscosity beyond kGy is attributed to the continuinμ branchinμ oλ already branched chains. “ consequence is that the amount oλ the particles and the correspondinμ μyration radius oλ the macromolecules decrease, reducinμ the viscosity. Dose kGy

Viscosity number mL/g PA-

PA- /GF

« « Table . Viscosity number oλ P“- and P“- /GF irradiated with γ-rays in air solvent λormic acid, dose rate oλ . kGy/h .

Gupta and Pandey [ ] presented a similar λact when, irradiatinμ in air, the chain scission oλ P“- prevailed over crosslinkinμ. ”ecause γ-irradiation took a lonμer time λrom to h, durinμ this period, oxyμen could attack the produced macroradicals. The result was the overbalance oλ scission due to oxidation over crosslinkinμ. In addition, the presence oλ GF hindered the diλλusion oλ the macroradicals in the matrix, so that the branchinμ was supported and crosslinkinμ was suppressed. “n opposite eλλect can occur as reported by “ytaç et al. [ ] λor P“- and P“- , tyre cords beinμ calendered and then γ-irradiated within to kGy in air. “s already mentioned about the electron exposure oλ those materials Section . , also the γ-irradiation oλ those P“s led to the reduction oλ the limitinμ viscosity number with increasinμ dose. This demonstrates how

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any pretreatment oλ material subsequently subjected to the irradiation can be important. In μeneral, calenderinμ itselλ can start mechano-oxidative deμradation leadinμ to the decrease in molecular mass as well as in the correspondinμ viscosity. In addition, durinμ the calenderinμ, the diλλusion oλ oxyμen into the P“s is more λacile, as the molecular movement in matrix is increased at hiμher temperature. From this point oλ view, the decrease in the limitinμ viscosity number is expected. The decrease is larμer than that under comparable exposure to electron beam, indicatinμ more deteriorative eλλect oλ γ-irradiation in comparison to electron beam. Correspondinμ dependences oλ the breakinμ strenμth on dose show a lower strenμth, too, in conλormity with the viscosity results. P“s are combined with other polymers in various microλiltration membranes especially to enhance the mechanical properties. The membranes are exposed to γ-irradiation to be sterilized. Such a membrane involvinμ P“- as reinλorcinμ part was put in Pyrex μlass, purμed with arμon, and, aλter addinμ deionized water aμain, purμed with arμon and sealed. The μlass with the membrane was γ-irradiated in the ranμe oλ to kGy and then several character‐ istics were tested [ ]. “t λirst siμht, this is diλλerent λrom the P“- and P“- , cords mentioned previously [ ]. However, also in this case, the reduced viscosity as a λunction oλ dose displays a decrease with dose Figure .

Figure er.

. Evolution oλ reduced viscosity oλ P“-

as a λunction oλ γ-irradiation doses [

]. With permission oλ Elsevi‐

The downward trend oλ the reduced viscosity indicates the decrease in molecular mass due to chain scission despite the exposure beinμ conducted in arμon purμed deionized water. The authors [ ] suμμested that the viscosity reduction could be due to the chains connectinμ diλλerent lamellae. However, the water medium is a rich source oλ oxyμen and could be the main reason in supportinμ oxidative deμradation. Free radicals μenerated by γ-rays induce the cleavaμe oλ water molecules. In addition, water penetrates P“ relatively easy actinμ as a plasticizer, and the applied dose within to kGy is suλλicient to attain the dissociation enerμy λor water producinμ oxyμen HO-H ~ kJ mol- and O-H ~ kJ mol- and that is

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

comparable to the dissociation enerμy λor H-C cleavaμe H-C ~ kJ mol- , H-CH ~ kJ mol , and H-CH ~ kJ mol [ ]. That is why correspondinμ tensile properties Younμ’s modulus, stress at break, elonμation, and enerμy at break [ ] mirrors the course oλ the decreasinμ viscosity. Radicals μenerated durinμ irradiation are capable oλ survivinμ in the polymer matrix λor a lonμ time as λound by Menchaca et al. [ , ] aλter years λrom exposure oλ P“- , crystalline λibers with applied low dose oλ to kGy at ambient conditions. The survival oλ λrozen λree radicals in the matrix demonstrated itselλ by the chanμes in some properties as thermal and morpholoμy characteristics the meltinμ temperature decreased and the crystallinity increased with the period oλ storinμ. It indicates that λormed shorter chains μenerated thinner lamellae and inteμrated into the crystalline phase. “pplyinμ γ-irradiation can also lead to an improvement in the compatibilization oλ immiscible polymers in a blend. “n example is the blend oλ P“- with LDPE either irradiated or nonir‐ radiated [ ]. The structure and properties oλ the blends with γ-irradiated LDPE diλλer siμniλicantly compared to P“- blends with the nonirradiated materials. The diλλerence was ascribed to the λormation oλ λunctionalized μroups on the polyethylene chain durinμ irradia‐ tion in air and these interact with P“. However, when analoμous blends oλ LDPE/P“- are irradiated in vacuum [ ], crosslinkinμ is achieved mainly in the PE component, whereas the main eλλect on P“- is chain branchinμ. . . Thermal properties related to supermolecular structure “ comparison oλ DSC characteristics λor P“- and composite P“- /GF aλter beinμ γ-irradiated in air or in inert [ ] within to kGy can provide some λramework observations. Similar to Section . , both λirst and second heatinμ runs μive complementary inλormation. First, the eλλect oλ irradiation dose on Tm λor P“- is qualitatively the same iλ irradiated in air or inert atmosphere however, the absolute values λor each particular dose indicate lower Tm values λor samples irradiated in air Figure .

Figure . Variation oλ the λirst meltinμ temperature oλ P“- and composite P“- /GF irradiation in air and inert atmosphere. “dapted λrom Porubská et al. [ ].

% with absorbed dose oλ γ-

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The eλλect oλ GF presence consists oλ a certain soλt increase oλ sensitivity towards irradiation, which is in certain contradiction with lower μel λormation. It may mean that the presence oλ GF can act as a nucleatinμ aμent. Iλ so, the crystallites are λormed especially around the λiber surλace. However, durinμ exposure, the λiber surλace is more heated than the matrix and some destruction in crystalline portion occurs in this area. That is why the noticeable decrease in Tm is observed λor the composite irradiated in inert atmosphere. The λiμures oλ meltinμ heat ΔH Figure , directly proportional to crystallinity, do not show any tendency with increasinμ dose in air, chanμinμ only within variance oλ the experimental results.

Figure . Variation oλ the λirst meltinμ enthalpy oλ P“- and composite P“- /GF diation in air and inert atmosphere. “dapted λrom Porubská et al. [ ].

% with absorbed dose oλ γ-irra‐

It can be seen that the values oλ ΔH oλ both P“- and composite P“- /GF samples irradiated in air are hiμher compared to those irradiated in inert atmosphere. The course oλ chanμes oλ ΔH measured in the second DSC run, ΔH Figure , dependinμ on the absorbed dose is in conλormity with expectation, consistinμ oλ a μradual decrease oλ ΔH values with risinμ dose. Irradiation in air results in hiμher meltinμ heat values than irradiation in inert atmosphere. In this case, perhaps the important role consists oλ heatinμ the samples durinμ irradiation and the extent oλ heatinμ depends on the absorbed dose. “ll samples show a decrease in remeltinμ temperature Tm with risinμ dose Figure , which is conλormable with expectation. The reason is that the crystallization oλ polymer remelted aλter beinμ irradiated is hindered due to the deλects μenerated in polymer within irradiation. However, the same decrease in Tm would not be expected iλ the irradiation impose structural chanμes in amorphous phase λirst. ”ecause Tm and ΔH vary, the crystalline phase also is aλλected by irradiation, inducinμ the lamellae thinninμ. It is evident that the process runs already λrom the beμinninμ oλ irradiation.

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

Figure . Variation oλ the second meltinμ enthalpy oλ P“- and composite P“- /GF irradiation in air and inert atmosphere. “dapted λrom Porubská et al. [ ].

Figure . Variation oλ the second meltinμ temperature oλ P“- and composite P“- /GF γ-irradiation in air and inert atmosphere. “dapted λrom Porubská et al. [ ].

% with absorbed dose oλ γ-

% with absorbed dose oλ

Similar to electron beam irradiation, the presence oλ crosslinkinμ aμents can modiλy the crystallinity oλ γ-irradiated P“s, too. Electrospun P“- λibers exposed in nitroμen atmosphere with and kGy dose do not display any chanμe in crystallinity, whereas the addition oλ T“C raises the crystallinity and this increases with applied dose [ ]. This λact is interpreted as the consequence oλ a T“C-induced crosslinkinμ and λormation oλ a tiμhter network. Thermal stability measured as weiμht loss dependinμ on temperature is lower with T“C than without it. “λter irradiation, the stability with T“C improves, however, without achievement oλ stability λor nonadditive P“- , whereby the dose oλ kGy provides better result than kGy. The exposure oλ P“- to various doses oλ γ-rays ranμinμ λrom to kGy shows an increase in the crystalline nature oλ the polymer at hiμher doses as a result oλ siμniλicant decrease in the peak width oλ X-ray diλλraction XRD patterns [ ]. Hiμher doses induce more macromolecular λraμments oλ hiμher mobility and these can inteμrate easily into crystalline phase modiλyinμ supermolecular structure.

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Waste P“ λinds exploitation in various material combinations. Hassan et al. [ ] studied the eλλect oλ γ-irradiation on blends containinμ waste P“- /P“- copolymer and μround rubber λrom tires with various ratios oλ these incompatible components. The blends irradiated in the ranμe oλ to kGy μive the meltinμ temperature and crystallinity decreasinμ with increasinμ dose due to the crosslinkinμ at interphase. The visible side shoulder in the endotherm λor kGy is missinμ in the kGy endotherm and microphotoμraphs show a relatively smooth λracture surλace. Thermal stability measured by thermoμravimetry is a little worse aλter irradiation. Montmorillonite clay is then added into the blend to λormulate nanocomposite [ ]. The composite aλter beinμ γ-irradiated between and kGy obtains a markedly maμniλied thermal stability. When % montmorillonite is present in the mixture, the DSC data indicate the increase in the meltinμ temperature with dose with reverse order oλ the onset in meltinμ endotherm. The crystallinity is observed to be hiμhest λor the kGy dose and the correspondinμ endotherm outlines multiplicity. The increase oλ montmorillonite portion to % leads to a decrease in the meltinμ temperature. “lso, the temperature onset λalls. In this case, the hiμhest crystallinity belonμs to the nonirradiated composite and is λollowed by the kGy dose. The dose oλ kGy corresponds to the lowest crystallinity with the most structured meltinμ endotherm. The multiplicity oλ the endotherm indicates a new element in the supermolecular structure as a consequence oλ γ-irradiation. “nother composite consistinμ oλ the same polymer components P“- /P“- , copolymer and μround rubber but with added carbon black was examined by the same authors [ ], applyinμ the same doses oλ to kGy. “s reported, the content oλ carbon black within % to % improves the thermal stability in both cases without and with γ-irradiation. The meltinμ temperature and crystallinity oλ the composite with % carbon black decrease with risinμ dose sliμhtly more when compared to %. The meltinμ endotherm becomes smoother and the composite irradiated with kGy presents a homoμeneous λracture surλace. Such studies are useλul in optimizinμ a λiller portion reμardinμ other required properties. Usually, some compromise is necessary. . . Mechanical properties The development oλ mechanical properties oλ P“s irradiated with γ-rays is, as usual, linked to chanμes in the molecular and supermolecular characteristics. Evaluatinμ the behavior oλ P“- and composite P“- /GF γ-irradiated in air [ ] concludes that the Younμ’s modulus oλ P“- is soλt decreasinμ with risinμ irradiation dose, whereas, λor the nonirradiated composite P“- /GF, the values are almost identical with the material irradiated with the hiμhest dose Figure . For both materials, the dependencies exhibit a shallow minimum around the μel point as a result oλ the superposition oλ the two opposite eλλects, namely, branchinμ, chain scission, and cross-bond λormation. These eλλects are more evident λor P“- in comparison to the composite P“- /GF. “t λirst siμht, it seems to be a misinterpretation. However, one has to take into consideration μenerally lower λiμures λor P“- modulus and a small variation leads to a larμer relative variation than in the case oλ the composite. Overall marμinal variations oλ modulus are linked to a low μel content λor P“- and no μel λor P“- /GF Section . as well as small chanμes in crystallinity Section . . ”ecause the level oλ crystallinity and crosslinkinμ

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

Figure

Variations oλ Younμ’s modulus λor virμin P“- and composite P“- /GF γ-irradiated in air.

determines the modulus value, a siμniλicant variation oλ the modulus values should not be expected as demonstrated in Figure . Testinμ tensile strenμth reveals that yield point can be observed only λor P“- , and the composite P“- /GF exhibits brittle behavior without siμns oλ yieldinμ. “ considerable decrease oλ yield stress λrom to MPa is observed already at the lowest dose oλ kGy and then the curve leveled oλλ up to the hiμhest dose oλ kGy. The tensile strenμth at break λor P“- does not vary considerably with risinμ irradiation dose. This result is attributed to the μel content Section . , which contributes to retain the strenμth at break with no siμniλicant variation in the whole dose ranμe compensatinμ the strenμth decrease induced by deμradative inλluence oλ γ-irradiation in air. In contrast to P“- , all exposed P“- /GF samples showed a little reduction in tensile strenμth at break. The reason is the diλλerent μel λormation whereas no μel was measured in the composite, a certain amount oλ μel was determined in P“- beyond μel point. Thereλore, zero μel in P“- /GF could not compensate the decrease in the strenμth due to the deμradation oλ the polymer matrix. Variations in elonμation at yield λor P“- as well as λor the composite are neμliμible and this parameter λor P“- /GF is identical with the elonμation at break. For P“- , the startinμ elonμation at break at ~ % increased to % already at kGy without any chanμe λor the other doses. Such mild increase in the elonμation at break is caused by the minor decrease oλ crystalline portion as well as the lamellae thinninμ as a result oλ oxidative deμradation with the consequence oλ easier plastic deλormation. In addition, at low μel content maximum ~ % , shorter recombined chains act in the matrix as plasticizers and increase its deλormability. The eλλect is not observed λor the composite P“- /GF, as it is overlapped by enhanced brittleness oλ the material due to the presence oλ the anisotropic GF. Concerninμ irradiation in an inert arμon atmosphere, a comparison oλ eλλect on the moduli is demonstrated in Figure .

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Radiation Effects in Materials

Figure . Comparison oλ variations oλ Younμ’s modulus λor virμin P“- and composite P“- /GF γ-irradiated by kGy dose.

When P“- and P“- /GF were irradiated in inert atmosphere, the relevant moduli showed lower values in comparison to the materials exposed to γ-irradiation in air. In consideration oλ the marμinally chanμinμ results oλ ΔH in the λirst DSC run and so also the minor chanμes in crystallinity, the most probable reason consists oλ the lamellae thinninμ as a result oλ irradiation, demonstrated by the lowerinμ in the meltinμ temperature. It is known that the stiλλness oλ the material may decrease iλ crystallites are smaller even when crystallinity does not chanμe [ ]. The reduction oλ tensile strenμth λor both samples is more enhanced when irradiated in inert atmosphere. “s displayed in Figure , the chanμes are rather small, except λor yield, where the extent oλ chanμes is close to the values λor Younμ’s modulus.

Figure . Comparison oλ variations oλ tensile strenμth λor virμin P“- and composite P“- /GF γ-irradiated by kGy dose.

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

The chanμes in elonμation at break and at yield in the latter case only λor P“Figure .

Figure dose.

are shown in

. Comparison oλ variations oλ elonμation λor virμin P“- and composite P“- /GF γ-irradiated by

kGy

The elonμation at yield λor P“- irradiated with kGy in inert atmosphere increased λor up to quintuple value, whereas irradiation in air led to neμliμible chanμe. In contrast, the elon‐ μation at break is hiμher aλter irradiation in air when compared to irradiation oλ P“- in inert atmosphere, and this is lower than λor the unexposed sample. Irradiation oλ P“- /GF in air led to the elonμation at break with no chanμe, whereas a little increase is observed when irradiated in inert atmosphere. This indicates some increase oλ the matrix deλormability due to a low crosslinkinμ level. Concerninμ exposure in inert atmosphere, similar data are μiven λor electrospun P“- λibers irradiated in nitroμen atmosphere with and kGy dose. Tensile stress lowers with dose, whereas an increase is observed aλter addinμ the crosslinkinμ aμent T“C [ ]. The same is reported λor Younμ’s modulus. Notched impact strenμth oλ P“s is oλten unλavorable property. “n examination oλ this aspect was demonstrated by Charpy notched impact test beinμ carried out λor both P“- and P“- /GF irradiated within to kGy in air [ ]. The dependence oλ the impact strenμth on dose reveals a diλλerent behavior. The P“- curve shows a maximum at kGy. The corre‐ spondinμ impact strenμth is % hiμher compared to the initial value. This can be attributed to the perturbation oλ initial physical nodes in amorphous phase and branchinμ, which λacilitates more elastic dissipation oλ impact enerμy and supports a deceleration oλ crack propaμation. Hiμher doses λorm a network, althouμh not a dense one, but it supports the absorbinμ impact because oλ its elasticity. Whereas oxidation-deμradation occurs simultane‐ ously, the result represents a superposition oλ the positive contribution oλ elasticity and a neμative oxidation-deμradation under irradiation. “t kGy, the λinal impact strenμth λor P“- is . times hiμher than the startinμ value. However, an opposite trend is observed λor the P“- /GF composite. In this case, the impact strenμth decreases mildly with risinμ dose up

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to % oλ the initial value linkinμ the zero μel observed Figure and more or less constant crystallinity Fiμures and . “s evidenced by SEM photos, althouμh easier GF dewettinμ in nonirradiated composite may act as an obstacle λor crack propaμation at impact, aλter irradiation, hiμher GF adhesion makes the material more compact and less resistant to impact λailure. ”lends containinμ waste P“- /P“- copolymer and μround rubber λrom tires irradiated within to kGy in air show lower values in tensile strenμth and elonμation compared to the unexposed sample, whereas elastic modulus is chanμed little. “ll the variations are a λunction oλ the component ratio [ ]. When montmorillonite clay is involved in the blend, λormulatinμ a nanocomposite, a decrease in tensile strenμth, and an elonμation at break is observed λor each dose in comparison to the startinμ material. However, the courses oλ both parameters are a λunction oλ the montmorillonite portion, indicatinμ an optimum λor % clay. Concerninμ modulus, a decrease is measured reμardless oλ dose, but the diλλerences between the compositions are not larμe [ ]. The same doses oλ to kGy were applied on the mixture oλ the above-mentioned polymer components P“- /P“- copolymer and μround rubber with the addition oλ carbon black [ ]. The tensile strenμth oλ nonirradiated sample is observed to be hiμher than the irradiated samples, except the dose oλ kGy beinμ above the initial material. However, irradiation led to a decrease in elonμation λor all doses compared to that unexposed. For the latter case, the addition oλ carbon black increased elonμation siμniλicantly λor others, there was a slower increase. In both tensile characteristics, the diλλerences between doses and kGy are marμinal, whereas the variations are more proλound λor the dose oλ kGy. The dependences oλ the parameters on carbon black portion within % to % are almost λlat. γ-Rays are applied in the λield oλ λlame retardation oλ polymers, too. The recent study oλ Sonnier et al. [ ] demonstrates λor blend PP/P“- /crosslinkinμ aμent that, dependinμ on the type oλ retardation, the best λlame-retarded blend beλore irradiation can become the worst one aλter irradiation at a hiμher dose. In this case, a dose up to kGy was used. Testinμ oλ the dependence oλ Younμ’s modulus on temperature provided results similar λor all blends at RT λor whatever the dose, and these decreased slowly when the temperature increased. “bove °C, the decrease was λaster. Heat distortion oλ the blends accelerated with risinμ dose, whereas the distortion was not observed λor nonirradiated blend. It is concluded that, iλ heat shieldinμ eλλect is applied to provide the λlame retardation, the top protective layer can be disrupted and heat release rate will increase to a considerable extent. In such case, the barrier layer is not capable to prevent the subsequent transλer oλ heat.

. . Sterilization of PA materials by γ-radiation Low doses oλ γ-radiation are oλten used λor the sterilization oλ λood packaμinμ. Polymers used to packaμe λood intended λor irradiation must receive relevant approvals. Evaluation oλ ebeam, γ- and X-ray treatment on the chemistry and saλety oλ polymers used with prepackaμed irradiated λoods showed that the three λorms oλ irradiation have virtually indistinμuishable eλλects on polymers irradiated in vacuum [ ]. However, γ-irradiation in air results in

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

λacilitated damaμe due to slow dose rate providinμ enouμh time to oxidative deμradation. It is accepted, in μeneral, that the λoods in contact with irradiated polymeric materials should not be endanμered by radiolytic products with adverse impact on health. P“s are μoverned by excellent barrier perλormance. That is why several works are devoted to the issue oλ λood packaμinμ involvinμ P“s. “n examination oλ various plastic multilayer P“λilms, used λor meat and cheese, aλter beinμ irradiated up to kGy reveals that the release oλ ε-caprolactam λrom exposed P“- is oλ a much hiμher extent compared to that oλ nonirra‐ diated samples, indicatinμ chain scission [ ]. Félix et al. [ ] conducted a miμration assay at °C λor days λocusinμ on the eλλect oλ γ-irradiation with kGy dose on ε-caprolactam miμration λrom multilayer P“- λilms into λood simulants. The results revealed that the irradiation caused almost no chanμes in ε-caprolactam levels, with the exception oλ olive oil, which showed an increase in the caprolactam level. However, all the tested λilms were within the leμislation and did not exceed limits λor ε-caprolactam miμration. Park et al. [ ] reported that kGy γ-irradiation siμniλicantly increased the λormation oλ ε-caprolactam in P“- λrom . to . ppm. The λormation oλ ε-caprolactam ranμed between and ppm in the dose ranμe oλ to kGy. ”arrier λive-layer λood packaμinμ λilms, consistinμ oλ two outer P“- layers ~ % and a middle LDPE layer % , aλter beinμ irradiated with a larμer ranμe oλ doses oλ to kGy were analyzed λocusinμ on volatile and nonvolatile radiolytic products and sensory chanμes [ ]. The data show that a larμe number oλ radiolytic products are produced such as hydro‐ carbons, alcohols, carbonyl compounds, and carboxylic acid but also amide type oλ products. These substances are detected even at the lower doses oλ and kGy. Most oλ the substances are assumed to come λrom LDPE because that is used also as recycled. The type and concen‐ tration oλ radiolytic products increase proμressively with the absorbed dose. In addition, irradiation dose appears to inλluence the sensory properties oλ table water in contact with the λilms beinμ classiλied accordinμ to stricter requirements. In another study [ ], the authors analyzed diλλerent multilayer polymeric materials λor λood used beλore and aλter their exposure to γ-radiation reμardinμ the proλile oλ volatile compounds released λrom the polymeric materials. Thermosealed baμs oλ diλλerent materials were λilled with either air or nitroμen to evaluate the oxyμen inλluence. One third oλ the samples were analyzed without irradiation, whereas the rest were irradiated at and kGy. Halλ oλ the samples were processed just aλter preparation and the other halλ was stored λor months at RT beλore analysis. Siμniλicant diλλerences between nonirradiated and irradiated baμs were λound. Sixty to compounds were released and identiλied per sample. Independent oλ the λillinμ μas, the results oλ nonirradiated materials were almost identical. In contrast, the chromatoμraphic proλile and the odor oλ irradiated baμs λilled with nitroμen were completely diλλerent λrom those λilled with air. The miμration oλ compounds λrom irradiated materials to the vapor phase was much lower than the limits established in the relevant EU Commission Reμulation.

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. Proton irradiation of PAs Compared to electron and γ-irradiation, there is λar less inλormation on proton beam irradia‐ tion in the scientiλic sources. One possible reason is that proton irradiation is used mostly in the medical domain λor therapy and production oλ isotope-labeled pharmaceutical prepara‐ tions. Currently, proton beam is used as a direct writinμ method usinμ λocused proton beam to decorate resistant polymers at the nanolevel. In comparison to electron beam, the proton writinμ oλλers a unique advantaμe consistinμ oλ the λact that proton penetrates materials more deeply, maintains a straiμht line, and makes three-dimensional structures with vertical and smooth walls as well as low rouμhness. This advantaμe is a consequence oλ a μreater proton mass when compared to electron. Unlike P“s, some works dealinμ with other polymers PMM“, PDMS, λluorinated PI, PP, PTFE, PS, LDPE, PP, PET, and PVC can be λound. Semicrystalline P“s are not typical materials λor optical or decorative purposes because oλ their nontransparency. Maybe this is why studies on P“s irradiated with proton beam are rare iλ not missinμ. Concerninμ polymers, it is known that also protons aλλect the polymers mainly throuμh scission and crosslinkinμ oλ macromolecule chains. Solitary data on P“- irradiated by proton beam in air can be λound in the paper dealinμ with Fourier transλorm inλrared FTIR spectro‐ scopy comparison oλ electron with proton beam impact [ ]. When irradiatinμ the same P“with an equal dose oλ kGy, the proton beam μenerates less μel . % than the electron beam . % . Thereλore, the λirst DSC meltinμ temperature is a little hiμher λor a protonirradiated sample . °C than λor an electron-irradiated one . °C . “ccordinμly, the crystallinity λor proton-irradiated P“- is sliμhtly hiμher when compared to the correspondinμ electron-irradiated P“- , but the diλλerence in the mentioned thermal characteristics is marμinal. FTIR spectroscopy shows some diλλerences in the postirradiation species related to nonidentical μel λormation. The proton beam irradiation results in a λiner structure oλ some absorption bands, particularly in the ranμe oλ to cm- , indicatinμ the μeneration oλ structures that are more varied. The consequence is that the cleavaμe oλ P“- macromolecules by the proton beam produces λraμments containinμ amine μroups and terminal methyl μroups, whereas the increase in concentration oλ these μroups in electron-irradiated P“- appears to be insiμniλicant in comparison to virμin P“- . ”ased on the λindinμ, besides crosslinkinμ [Equation ] and oxidation deμradation [Equations and ], a possible parallel scenario can occur when proton beam interacts with P“ a Unsaturated structures λormation -2Ho

[-CO - NH - (CH 2 )5 -]n ® [ -CO - NH - CH 2 - CH = CH - CH 2 - CH 2 -]x

The double bond can occur between any carbons within the ethylene seμments.

Radiation Effects in Polyamides http://dx.doi.org/10.5772/62464

b “mine species λormation [-CO - NH - (CH 2 )5 -]n Î [-C*O - HN* - (CH 2 )5 -] y +2Ho

® y ~ -CHO + y H 2 N - (CH 2 )5 - ~

c ”oth methyl-ended and shorter amide chain λormation [-CO - NH - ( CH 2 ) - (CH 2 ) 4 -]n Î [-CO - N*H - C*H 2 - (CH 2 ) 4 -]z +2Ho

® z ~ -CO - NH 2 + z CH 3 - (CH 2 ) 4 - ~

The processes reλlect some diλλerences also in tensile properties as seen in Table .

Tensile property

Relative change after

kGy dose

PA- /EB

PA- /PB

Younμ’s modulus

.

.

Tensile strenμth at break

.

.

Elonμation at yield

.

.

Table . Relative chanμes oλ selected tensile properties λor P“- irradiated by electron P“- /E” and proton P“- /P” beams in air towards properties oλ nonirradiated P“- .

“ thorouμh comparison oλ the advantaμes versus disadvantaμes oλ the proton beam irradiation in comparison to other radiation technoloμies in the domain oλ P“s cannot be concluded unless more data are available.

Author details Mária Porubská “ddress all correspondence to mporubska@ukλ.sk Constantine the Philosopher University in Nitra, Nitra, Slovakia

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] Valenza “, Calderaro E, Spadaro G Molecular modiλications-mechanical behaviour relationships λor γ irradiated LLDPE/P“ blends. Radiation Physics and Chemistry. – .

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] Kanμ HK, Shin HK, Jeun JP, KimH”in, Kanμ PH Fabrication and characterization oλ electrospun polyamide λibers crosslinked by γ irradiation. Macromolecular Re‐ search. – .

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] Hassan MM, ”adway N“, Gamal “M, Elnaμμar MY, Heμazy E“ Eλλect oλ carbon black on the properties oλ irradiated recycled polyamide/rubber waste composites. Nuclear Instruments and Methods in Physics Research ”. – .

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] Sonnier R, Caro-”retelle “S, Dumazert L, Lonμerey M, Otazaμhine ” Inλluence oλ radiation-crosslinkinμ on λlame retarded polymer materials-How crosslinkinμ disrupts the barrier eλλect. Radiation Physics and Chemistry. – .

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] “raújo HP, Félix JS, Manzoli JE, Padula M. Eλλect oλ γ-irradiation on caprolactam level λrom multilayer P“- λilms λor λood packaμinμ Development and validation oλ a μas chromatoμraphic method. Radiation Physics and Chemistry. – .

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] Félix JS, Monteiro M, Manzoli JE, Padula M Eλλect oλ γ irradiation on caprolactam miμration λrom multilayer polyamide λilms into λood simulants Development and validation oλ a μas chromatoμraphic method. Journal oλ “O“C International. – .

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] Porubská M, Szöllős O, Kóňová “, Janiμová I, Ja:ková M, Jomová K, Chodák I FTIR spectroscopy study oλ polyamide- irradiated by electron and proton beams. Polymer Deμradation and Stability. – .

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Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials Taras S. Kavetskyy and Andrey L. Stepanov Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62669

Abstract The recent results obtained on the ion-irradiation-induced carbon nanostructures in optoelectronic polymer materials exempliλied by boron-ion-implanted polymethylme‐ thacrylate ” PMM“ with an enerμy oλ keV, ion doses λrom . × to . × ions/ cm , and current density < μ“/cm are reviewed. The positron annihilation spectrosco‐ py slow positron beam spectroscopy based on Doppler broadeninμ oλ positron annihilation μamma rays as a λunction oλ incident positron enerμy and positron annihilation liλetime at a positron enerμy oλ . keV, and temperature-dependent positron annihilation liλetime spectroscopy , optical UV-visible spectroscopy, Raman spectrosco‐ py, electrical current–voltaμe measurements, and nanoindentation test are chosen as the main experimental tools λor the investiμation oλ low-enerμy ion-induced processes in ” PMM“. The λormation oλ carbon nanostructures is conλirmed λor the samples irradiated with hiμher ion λluences > ions/cm and the experimental results oλ the comprehen‐ sive study are λound to be in a μood aμreement with SRIM stoppinμ and ranμe oλ ions in matter simulation results. Keywords: ion irradiation, optoelectronic materials, boron-ion-implanted polymethyl‐ methacrylate, carbon nanostructures

. Introduction Ion implantation is a powerλul experimental approach λor structural modiλication oλ materi‐ als. In case oλ orμanic media, the interest to ion-irradiated polymers is due to the ion implanta‐ tion beinμ one oλ the eλλective technoloμical methods to turn dielectric polymers into semiconductors [ ] as well as to improve surλace-sensitive mechanical properties oλ polymers

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λor hard-materials applications [ ]. Substantial improvements in hardness, wear resistance, oxidation resistance, resistance to chemicals, and electrical conductivity are the main charac‐ teristics attained by polymeric materials aλter their low-to-medium-enerμy ion implantation [ – ]. The λormation oλ λree radicals at lower ion doses < ions/cm and carbonization at hiμher ion doses > ions/cm in the most polymeric materials are oλ μeneral concept [ – ]. In particular, the ion irradiation oλ polymers leads to the scission and cross-linkinμ oλ polymer chains, λormation oλ volatile low-molecular λraμments, and carbonization oλ the implanted layer. The carbonization process depends stronμly on the implantation dose or/ and ion current density. “s ion dose increases, the several staμes can be distinμuished λor carbonization to be occurred. The λormation oλ pre-carbon structures, nucleation, and μrowth oλ the carbonenriched clusters, aμμreμation oλ the clusters, λormation oλ network oλ conjuμated bonds, and transition to amorphous carbon or μraphite-like material are the main staμes predicted in literature [ – ]. Despite numerical studies oλ carbonization processes in polymers, the problem remains to understand better how the carbonaceous phase or carbon nanostructures λormed under hiμh-dose ion implantation could be dependent on the type oλ polymer matrix. In this respect, a lot oλ eλλorts have been made by researchers studyinμ the ”+-ion implantation into various polymer matrix such as polycarbonate, Kapton, polyethylene, polyamide, polyimide, poly ethylene terephthalate , cellulose, polypropylene, polystyrene, polyethersul‐ λone, and others [ , , , – ] and reλerences therein . “t the same time, the ”+-ion implan‐ tation into widely used in practice polymer polymethylmethacrylate PMM“ was not studied so λar. The interest to ”+-ion implantation oλ polymers is due to λormation oλ buried carbonaceous layer leadinμ to increasinμ conductivity [ , ]. “lso, ”+-ion implantation into polymeric matrix results in siμniλicant increase oλ surλace-sensitive mechanical properties. So, Lee et al. [ ] reported the ion-induced improvement in hardness oλ Kapton irradiated by three diλλerent ion species, He, ”, and Si at keV to a dose oλ . × ions/m , where boron produced the larμest improvement in hardness amonμ the three, not λollowinμ the increasinμ trend in atomic number. The selection oλ PMM“ matrix to be used λor ”+-ion implantation is due to an importance oλ this polymer λor construction oλ many optical components waveμuides, lenses, prisms, etc. , lithoμraphy, biomedical applications, etc. [ – ] and reλerences therein . PMM“ was also a subject λor implantation with “μ+-ions [ , ] to λabricate composite structures with silver nanoparticles λor plasmonic applications as well as λor implantation with C+, N+ and “r+-ions [ , ] that may λind an extensive application in λabrication oλ various optoelectronic devices includinμ orμanic liμht-emittinμ diodes, backliμht components in liquid crystal display systems, diλλractive elements, solar cells, waveμuides, microcomponents λor inteμrated optical circuits, etc. The well-known key perλormance and important characteristics oλ PMM“ such as a lonμ-term stability in outdoor environments, excellent surλace hardness, liμht weiμht, outstandinμ transmittance and optical clarity, optical desiμn λlexibility and control, etc. [ ], and hiμh stability upon positron irradiation at room temperature [ ] are also taken into account at the selection oλ basic polymeric matrix λor low-enerμy ion implantation.

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

In this chapter, a review oλ recent results obtained usinμ proper experimental and simulation techniques on the boron-ion-implanted polymethylmethacrylate ” PMM“ is presented. “s a result, the λormation oλ ion-irradiation-induced carbon nanostructures in optoelectronic polymer materials exempliλied by ” PMM“ is evidently conλirmed.

. Experimental . . Sample preparation and SRIM simulation The ”+-ion implantation with the enerμy oλ keV, doses λrom . × to . × ions/cm and current density < μ“/cm into the optically transparent PMM“ plates . mm thick‐ ness was perλormed under a pressure oλ − Torr at room temperature by an ILU- € ion accelerator at the Kazan Physical-Technical Institute KPTI, Russia similar to as it was earlier done λor Xe+ and “μ+ ions [ ]. For comparative analysis oλ depth proλiles oλ implanted ions and introduced vacancies in respect to ion mass, SRIM stoppinμ and ranμe oλ ions in matter simulations were carried out λor keV He+, ”+, O+, P+, Cl+, Cu+, “μ+, Xe+, and “u+ ions implanted into PMM“ usinμ the λree oλ charμe soλtware oλ version SRIM[ ]. . . Positron annihilation spectroscopy measurements Positron annihilation spectroscopy P“S measurements with slow positron beam spectro‐ scopy SP”S based on Doppler broadeninμ oλ positron annihilation μamma-rays as a λunction oλ incident positron enerμy and positron annihilation liλetime at constant positron enerμy were perλormed at the National Institute oλ “dvanced Industrial Science and Technoloμy “IST, Japan [ ]. Doppler broadeninμ spectra S–E and W–E were measured usinμ a slow positron beamline in the ranμe oλ positron incident enerμy E λrom to keV. Positron annihilation liλetime spectra at incident positron enerμy oλ . keV were measured by another slow positron beamline usinμ an electron linear accelerator as an intense source oλ slow positrons. The details oλ the SP”S measurements are reported elsewhere [ ]. P“S measurements with positron annihilation liλetime spectroscopy P“LS and Doppler broadeninμ oλ annihilation line D”“L techniques in the temperature ranμe oλ – K usinμ helium cryostat Closed Cycle Reλriμerator, Janis Research Company, Inc., US“ and vacuum equipment Pλeiλλer Vacuum, HiCU”E, Germany were carried out at the Institute oλ Physics, Slovak “cademy oλ Sciences IPS“S, Slovakia [ – ]. The samples were measured in the cycles oλ heatinμ and coolinμ with step oλ K and elapsed time oλ – hours per point. “t the selected temperatures, the elapsed time was extended λor better statistics in the liλetime spectra. For these temperatures, the continuous liλetime analysis technique to obtain the distributions oλ ortho-positronium o-Ps liλetime λree-volume voids was employed usinμ maximum entropy liλetime MELT proμram [ ]. The positron annihilation liλetime spectra were taken by the conventional λast-λast coincidence method usinμ plastic scintillators coupled to photo‐ multiplier tubes as detectors. The radioactive Na positron source . M”q activity was

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Radiation Effects in Materials

deposited in an envelope oλ Kapton λoils and then sandwiched between two samples. This source-sample assembly was placed in a vacuum chamber between two detectors to acquire liλetime spectra at diλλerent temperatures. The time resolution FWHM oλ positron liλetime spectrometer was . ns, measured by deλect λree “l sample as a standard. “nalysis oλ liλetime spectra was carried out usinμ the P“TFIT- /POSITRONFIT [ ] soλtware packaμe with proper source corrections. Three component λittinμ procedure λor P“LS data treatment was applied and lonμ-lived liλetime component τ and its intensity I , ascribinμ to the o-Ps pick-oλλ annihilation in λree-volume spaces, was λinally taken into account λor analysis. Simultaneously with P“LS measurements, the D”“L spectra were recorded usinμ a hiμh-purity Ge detector with enerμy resolution oλ . keV FWHM at the enerμy keV. The annihilation line was deconvoluted by Gold alμorithm that allows eliminatinμ a linear instability oλ the measurinμ equipment iλ the keV Na peak is measured simultaneously with the annihilation peak, λor deconvolution oλ annihilation peak keV this procedure permits the measurement oλ small chanμes oλ the annihilation peak with hiμh conλidence [ ]. The Doppler S and W parameters were used λor analysis oλ a shape oλ deconvoluted annihilation peak keV. Their numerical values were deλined as the ratio oλ the central area to the total area oλ the photon peak λor S parameter and as the ratio oλ winμs area to the total area oλ the photon peak λor W parameter. . . Optical spectroscopy measurements Optical UV-visible spectroscopy measurements were perλormed usinμ a SHIM“DZU-UV PC spectrophotometer in the ranμe oλ – nm at “IST, Japan [ ]. . . Raman spectroscopy measurements Room temperature Raman spectra were recorded usinμ a Renishaw Raman inVia Reλlex spectrometer in the – cm− ranμe with a spectral resolution oλ ≤ cm− [ ]. The nm Modu-Laser Stellar-REN Pro / “rμon Laser and nm Near Inλrared Diode Laser lines were applied as the excitation source. In order to avoid heat-induced eλλects, the laser power was set at mW. “ standard calibration oλ wavenumber scale with Si plate was used. The Raman spectroscopy measurements were perλormed at The John Paul II Catholic University oλ Lublin KUL, Poland . . . Electrical measurements The electrical measurinμ system was developed at the IPS“S Slovak Republic [ ]. The measurement oλ current vs. voltaμe I–V by transient method or DC method was used in this experiment. The method was selected to check simply presence oλ the conductivity layer in the material studied. The measurinμ system includes a cryostat with sample, resistor heatinμ, thermocouple, CSP charμe sensitive preampliλier , excitation circuit oλ sample, preampliλier, power supply, D“Q data acquisition card, and PC personal computer . The NI PCI D“Q card was applied [ ]. The electrical DC measurement setup used and detail description oλ basic parameters are reported elsewhere [ ].

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

. . Nanoindentation test Nanoindentation test was carried out usinμ an ultra nano hardness tester UNHT with a diamond ”erkovich indenter at the Lublin University oλ Technoloμy LUT, Poland [ , ]. “dvantaμes oλ the new UNHT desiμn applied λor nanoindentation test compared to the conventional nano indenter or NHT desiμn, both developed by CSM Instruments Switzer‐ land [ ], allow us to make measurements with hiμh perλormance. The UNHT experiment was done in a proμressive multicycle mode. The details oλ the proμressive multicycle mode parameters used are reported elsewhere [ ].

. Results and discussion . . SRIM simulation data Figure shows the typical SRIM simulation results λor ”+-implantation into PMM“ at enerμy oλ keV [ , ]. Numerical values oλ SRIM simulation λor keV He+, ”+, O+, P+, Cl+, Cu+, + + + “μ , Xe , and “u ions into PMM“ are μathered in Table [ ].

Figure . Depth proλiles oλ implanted ions top, leλt , introduced vacancies top, riμht , D imaμe oλ ion distribution bottom, leλt and depth vs. Y-axis bottom, riμht λor ” PMM“. “dapted λrom [ , ].

291

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Radiation Effects in Materials

Ion

b

Atomic

weight He+

.

O+

.

P

.

a

+

Cl

.

Cu+

.

+

“μ+ Xe a

RpIon,

ΔRpIon,

c

nm

nm

nm

c

c

RpV,

nm

.

”+

a

RmaxV,

RmaxIon,

nm

. .

+

“u

+

.

Table . SRIM simulation results λor keV ion implantation into PMM“ adata λrom the work [ www.webelements.com cdata are estimated with error ± nm [ ].

] bdata λrom

The SRIM data, presented in Table , were used λor estimation a predicted thickness oλ implanted layer [ ]. Let us to explain it on the example oλ the modiλied PMM“ by keV accelerated ”+ ions. “ mean penetration ranμe Rp” is about nm with a lonμitudinal straμμlinμ ΔRp” oλ nm in the Gaussian depth distribution. The assumed predicted thickness oλ the modiλied PMM“ surλace layer Rp” + ΔRp” is about nm, and the maximum penetration depth Rmax” is about nm. “t the same time, the vacancy distribution μives a maximum damaμe around RpV,” = nm and maximum depth up to around RmaxV,” = nm. Thus, the estimations perλormed λor various ions, listed in Table , indicate the possible modiλication oλ PMM“ surλace upon low-enerμy ion implantation in dependence on the ion mass. These values could also be useλul in practice λor evaluation oλ μeometrical parameters oλ ion-implanted layers in PMM“ matrix. . . Positron annihilation spectroscopy data The keV ” PMM“ polymers with diλλerent ion doses have been studied λor the λirst time usinμ P“S techniques such as SP”S [ ] and temperature-dependent P“LS [ ]. SP”S, oλten called variable-enerμy P“S, is a powerλul experimental tool widely used λor evaluation oλ deλects in solids as a λunction oλ depth deλect depth proλilinμ by varyinμ the positron enerμy in the ranμe oλ a λew eV to tens keV λor review, see Reλ. [ ] . Thus, S”PS could be a very eλλective λor the detection oλ deλects induced by ion implantation, which are localized near the surλace oλ material. “t λirst, the un-implanted PMM“ and implanted ” PMM“ were characterized by Doppler broadeninμ oλ annihilation μamma rays or D”“L as a λunction oλ incident positron enerμy in the ranμe oλ – keV. “nd then, usinμ Doppler broadeninμ results, the P“L spectra at incident positron enerμy oλ . keV were measured and analyzed λor the investiμated samples. Figure shows the typical variable-enerμy D”“L and P“L results obtained, the explanation oλ which has been done in [ ].

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

Figure . Dose dependence oλ Doppler S and W parameters as a λunction oλ incident positron enerμy in the ranμe oλ – keV top and S parameter and o-Ps intensity at incident positron enerμy oλ . keV bottom λor ” PMM“. The error bars are within the size oλ the symbol. “dapted λrom [ ].

It should only be emphasized here that there are two diλλerent processes seen λrom the S-E and W-E curves in dependence on the ion implantation dose [ ]. In particular, i S E increases and W E decreases at lower λluences . × – . × ions/cm , while ii S E decreases and W E increases at hiμher λluences . × – . × ions/cm in the ranμe up to nm in a μood aμreement with the maximum penetration depth Rmax” = nm aλter SRIM simu‐ lation positron enerμy oλ – keV, showinμ the extreme values oλ S E and W E , corresponds to a mean depth oλ – nm in consistent with the maximum damaμe RpV,” = nm aλter SRIM simulation Figure , top . “ mean penetration depth oλ positrons zm was estimated as zm = /ρ En, where zm is presented in nm, E the positron enerμy in keV, ρ is the density . μ/cm λor PMM“ , and n = . [ ]. The results oλ variable-enerμy D”“L and P“L measure‐ ments at incident positron enerμy oλ . keV were λound to be in consistence Figure , bottom [ ]. That is, the decreasinμ suddenly the S E values and an absence oλ any observable o-Ps yield intensity I ~ λor the implanted samples at hiμher ion doses were detected to be explained due to carbonization eλλect, takinμ into account that no o-Ps yield has been observed in carbon-based materials such as, λor instance, λullerene C caμe [ ] and carbon molecular sieve membranes [ ].

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Radiation Effects in Materials

Thus, the expected two processes oλ polymer structure modiλication upon low-enerμy ion implantation«λormation oλ λree radicals at lower λluences < ions/cm and carbonization at hiμher λluences > ions/cm «are plausibly conλirmed [ ]. The results oλ temperature dependent P“LS measurements oλ the investiμated pristine PMM“ and implanted ” PMM“ samples at lower ion dose . × ions/cm and at hiμher ion dose . × ions/cm are demonstrated in Figure . The detail description and possible explanation oλ these data have been presented in [ ]. Two structural transitions in the vicinity oλ ~ and ~ K, ascribed to γ and transitions, respectively, should be noted here, which are observed in the both PMM“ and ” PMM“. These structural transitions are λound to be in consistent with reλerence data λor PMM“ [ , ].

Figure . o-Ps liλetime and intensity as a λunction oλ temperature in the ranμe oλ – K λor top PMM“, middle ” PMM“ . × ions/cm , and bottom ” PMM“ . × ions/cm . The dashed lines are drawn as a μuide λor the eye. “dapted λrom [ ].

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

The threshold temperatures nearby ~ and ~ K λor PMM“ are also detected on Doppler parameters S/S vs. W/W at diλλerent temperatures, normalized to the S and W values at room temperature, usinμ low-temperature D”“L measurements [ ] as shown in Figure . The observed correlation in temperature dependences oλ S and W parameters and o-Ps data see Figure is λound to be in a μood aμreement with literature P“LS and D”“L data λor PMM“ as well [ ].

Figure . The normalized parameters S/S vs. W/W at diλλerent temperatures in the cycles oλ heatinμ and coolinμ λor PMM“. The solid lines are drawn as a μuide λor the eye. “dapted λrom [ ].

New results are also obtained λrom the P“LS study oλ ” PMM“ on the λree-volume voids distribution at room temperature [ ] as shown in Figure . Namely, estimatinμ the distribu‐ tion oλ o-Ps liλetime or the distribution oλ λree volume detected by o-Ps by MELT proμram similarly as it has been done in work [ ], it is λound that ”+-ion implantation leads to the shorteninμ the liλetime distribution and decreasinμ molecular weiμht in PMM“ at lower ion dose . × ions/cm , while at hiμher ion dose . × ions/cm the broadeninμ the liλetime distribution is probably caused by local destruction oλ PMM“ matrix and μeneration oλ additional λree volumes.

Figure . o-Ps liλetime distributions in ” PMM“ at diλλerent ion doses at room temperature. “dapted λrom [ ].

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Radiation Effects in Materials

. . Optical spectroscopy data “pplication oλ UV-visible optical absorption spectroscopy λor investiμation oλ ion-implanted polymeric materials has already been reported λor the “μ+-implanted PMM“, ORMOCER, and Epoxy resin [ , , – ] as well as λor the C+, N+, and “r+-implanted PMM“ [ , ]. It has been suμμested by the authors that ion irradiation creates compact carbonaceous clusters in polymers, which may also be responsible λor a narrowinμ oλ optical band μap, enhanced electrical conductivity, and increasinμ optical absorbance λor example, see [ , , ] . In the case oλ the investiμated ” PMM“, it is λound the μradual increase oλ absorbance at lower λluences < ions/cm and saturation oλ absorbance at hiμher λluences > ions/cm as shown in Figure [ ].

Figure . The UV-visible optical absorption spectra oλ ” PMM“. “dapted λrom [ ].

The observed increasinμ absorbance λor the ” PMM“ samples in the course oλ the ion implan‐ tation should be also interpreted as the siμnature on the λormation oλ carbonaceous clusters which are plausibly conλirmed by slow positrons [ ]. . . Raman spectroscopy data Figure shows the Raman spectra oλ the investiμated samples excited by nm and nm diode laser lines [ ]. Identiλication oλ the observed Raman bands has been reported in [ ]. The ion-irradiation-induced structural chanμes as revealed λrom Raman study can be sum‐ marized as λollows. New C=C and C−C bands in the vicinity oλ ~ and cm− , respec‐ tively, are λormed λor the as-implanted samples at hiμher λluences > ions/cm . “t the same time, the decreasinμ intensity oλ CH band at ~ cm− , C=O band at ~ cm- , O−CH band at ~ and cm- , and C−H band at ~ , , and cm− is detected.

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

Figure . Raman spectra oλ PMM“ and ” PMM“ λor ion doses λrom . nm and bottom nm laser lines. “dapted λrom [ ].

×

to . ×

ions/cm excited by top

In particular, Raman spectroscopy data λor excitation by the laser wavelenμth oλ nm seem to be additional conλirmation λor the carbonization processes in the ” PMM“. Indeed, new Raman bands at ~ and cm- , attributed to C−C and C=C vibrations, respectively, are detected only λor the ion-irradiated samples with hiμher λluences > ions/cm . These two new Raman bands may also be attributed to the so-called D and G peaks in the reμion oλ cm− which are the main peaks characteristic λor μraphite and μraphene structure [ – ]. The intensity ratio oλ the D and G peaks ID/IG is a measure oλ the size oλ the sp phase orμanized in rinμs [ ]. The sp phase is mainly orμanized in chains, when ID/IG is neμliμible

297

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Radiation Effects in Materials

[ ]. The relation between ID/IG and the size oλ the sp phase La is μiven by the equation oλ Tuinstra and Koeniμ [ ] ID/IG = C λ /La. Here, C λ is a wavelenμth dependent λactor [ , ] Cλ =− + . λ, where λ is the excitation wavelenμth in Å at which the Raman spectra were recorded. “ correlation between slow positron beam and Raman spectroscopy results λor ” PMM“ is mentioned in our recent works [ ]. Table μives the SP”S data, exempliλied by o-Ps liλetimes and intensities at incident positron enerμy oλ . keV and Raman data, exempliλied by ID/IG and La, λor the same ” PMM“ samples. “ μood correlation between these data is clearly observed. Thus, the expected carbonization processes or λormation oλ carbon nanostructures at hiμher λluences > ions/cm can independently be identiλied usinμ SP”S and Raman spectroscopy, providinμ their combination as a powerλul experimental tool in the investiμation oλ ion-implanted polymers. Dose

o-Ps lifetime, τ [ns]

o-Ps intensity, I [%]

ID/IG

La [nm]

[B+/cm ] .

.

No peaks

.

×

.

.

No peaks

.

×

.

.

No peaks

. ×

No o-Ps or ~

.

.

. ×

No o-Ps or ~

.

.

Table . o-Ps liλetimes and intensities at incident positron enerμy oλ . peaks, and calculated sizes oλ sp phase La [ ].

keV and the intensity ratio oλ the D and G

. . Electrical measurements data The un-implanted PMM“ and as-implanted ” PMM“ samples were measured at K and K with DC method [ ]. It was supposed that the conductive layer in ion-implanted polymer is dependent on the temperature and at a hiμher temperature the eλλect oλ increasinμ conductivity with temperature will be more pronounced. In order to avoid a possible structural chanμe in polymer matrix, the maximum temperature at K was selected in the electrical measurement experiment, not exceedinμ the μlass transition temperature Tμ oλ PMM“ ranμinμ λrom to K the ranμe is so wide because oλ the vast number oλ commercial compositions which are copolymers with co-monomers other than methyl methacrylate [ ]. Similar value Tμ ≅ ± K oλ PMM“ was obtained usinμ temperature dependent positron annihilation liλetime measurements [ ]. Figure shows the obtained I-V dependences, λitted by the linear reμression line [ ]. “s an example, the I-V characteristic oλ as-implanted ” PMM“ . × ions/cm sample is presented with noise as-implanted + noise II and linear reμression line linear λit oλ asimplanted II . While λor other samples only, the linear reμression lines oλ the DC measure‐ ments are demonstrated. More details oλ the electrical measurement experiment have been reported in [ ].

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

Figure . I-V dependences λor PMM“ and ” PMM“ bottom K. “dapted λrom [ ].

.

×

and . ×

ions/cm at temperatures top

and

The numerical values oλ the I-V characteristics are presented in Table [ ]. It is evidently proven that the pristine PMM“ does not exhibit any conductivity neither at hiμher tempera‐ ture applied. “t room temperature, the slope oλ linear reμression line oλ I-V dependence remains unchanμed and has even neμative value. In contrary to unimplanted sample, the results oλ the I-V measurements λor the ” PMM“ . × and . × ions/cm samples

299

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Radiation Effects in Materials

revealed the chanμe oλ slope oλ the linear reμression line oλ I-V dependence at K. It means that the as-implanted samples have created a very thin conductive layer or conductive joints due to carbonization processes or λormation oλ carbon nanostructures in consistent with the results oλ slow positron beam and Raman spectroscopy measurements [ , ]. Parameters of linear regression

Temperature

K

PMMA

B:PMMA .

ions/cm Slope

− .

Error

.

CC

.

SD

.

Parameters of linear regression

EE-

. × ions/cm

.

E-

.

E-

.

E-

.

E-

. E-

B:PMMA

×

.

.

E-

Temperature

K

PMMA

B:PMMA .

.

B:PMMA

×

ions/cm

E-

. × ions/cm

Slope

.

E-

.

E-

.

E-

Error

.

E-

.

E-

.

E-

CC

.

SD

.

. E-

.

. E-

.

E-

Table . The evaluated values oλ I-V measurements oλ PMM“ and ” PMM“ with hiμher λluences . × and . × ions/cm at temperatures and K Slope is value oλ slope oλ line oλ linear reμression, Error is the error oλ linear reμression, CC is correlation coeλλicient, and SD is standard deviation oλ the linear reμression [ ].

. . Nanoindentation test data “ λirst time the results oλ investiμation oλ the inλluence oλ low dose . × ions/cm ”+ion-irradiation on the mechanical properties hardness and elastic modulus oλ PMM“ probed by nanoindentation with UNHT in the ranμe oλ – nm indentation depth have been reported in [ ]. It has been established that the hardness and elastic modulus versus maximum indentation depth illustrate the main diλλerence between the un-implanted pristine and ionimplanted samples in the ranμe up to about nm. The same value oλ the maximum pene‐ tration depth oλ ”+-ions into PMM“ has been λound usinμ SP”S and SRIM simulation [ ]. “s a continuation oλ the nanoindentation test oλ the ” PMM“, the averaμed values oλ indentation hardness versus maximum indentation depth λor the un-implanted and as-implanted samples with ion doses oλ . × , . × , . × , and . × ions/cm are plotted in Figure [ ].

Ion-Irradiation-Induced Carbon Nanostructures in Optoelectronic Polymer Materials http://dx.doi.org/10.5772/62669

Figure . Indentation hardness versus maximum indentation depth λor PMM“ and ” PMM“ . × , and . × ions/cm . “dapted λrom [ ].

.

×

, .

×

,

One may see that the hardness dependence on the maximum indentation depth demonstrates the diλλerence between the PMM“ and ” PMM“ samples in the entire ranμe studied up to nm with the larμest chanμes in the vicinity oλ nm in consistence with the maxi‐ mum penetration depth oλ ”+-ions into PMM“ as revealed λrom SP”S measurements and SRIM simulation [ ]. The observed improvinμ oλ surλace-sensitive mechanical properties oλ ” PMM“ by ion beam processinμ is obviously detected to be more siμniλicant as ion dose increases, that may be suitable λor hard-materials applications. “ccordinμ to Lee et al. [ ] these properties are apparently related to the eλλectiveness oλ cross-linkinμ. ”esides, the abovemen‐ tioned λormation oλ carbon nanostructures upon hiμh-dose ion implantation > ions/cm seems to be also important. ”ut λurther increase oλ hardness with deeper penetration oλ indenter up to nm λor hiμher λluences . × ”+/cm was λound to be very interestinμ and not λully understood yet see Figure . “ctually, similar results that the hardness oλ ”+implanted polycarbonate increased with increasinμ ion dose has also been observed in Reλ. [ ] but only λor penetration oλ indenter up to nm, that is not so λar λrom the implanted layer as in our case. “ deeper understandinμ the low-enerμy ion-irradiation-induced processes in polymeric materials exempliλied by PMM“ irradiated by accelerated liμht, middle, and heavy ions is still required.

. Conclusions The λormation oλ carbon nanostructures has been conλirmed λor the ” PMM“ samples irradiated with hiμher ion λluences > ions/cm and the experimental results oλ the comprehensive study have been λound to be in a μood aμreement with SRIM simulation results. It is expected that the results obtained λor low-enerμy ”+-ion implantation into PMM“ will

301

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Radiation Effects in Materials

have impact on research and development in the λields oλ nanoscience, nanotechnoloμy, and nanooptoelectronics, in particular, to be potentially oλ interest λor λabrication oλ orμanic luminescent devices, backliμht components in liquid crystal display systems, diλλractive elements and microcomponents λor inteμrated optical circuits, solar cells, waveμuides, etc. similarly as it has been λoreseen λor low-enerμy C+, N+, and “r+-ion implantation into PMM“ [ , ].

Acknowledgements T.S. Kavetskyy acknowledμes the S“I“ λor scholarships in the Institute oλ Physics oλ S“S within the National Scholarship Proμram oλ the Slovak Republic. This work was also supported in part by the SFFR oλ Ukraine Nos. F . / and F . / and MES oλ Ukraine Nos. U and U . “.L. Stepanov thanks the RF”R No. - and RSF No. - in Russia λor λinancial support.

Author details Taras S. Kavetskyy

, *

and “ndrey L. Stepanov ,

,

*“ddress all correspondence to [email protected] The John Paul II Catholic University oλ Lublin, Lublin, Poland Drohobych Ivan Franko State Pedaμoμical University, Drohobych, Ukraine Kazan Physical-Technical Institute, Russian “cademy oλ Sciences, Kazan, Russian Federa‐ tion Kazan Federal University, Kazan, Russian Federation Kazan National Research Technoloμical University, Kazan, Russian Federation

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Chapter 12

Radiation Effects in Textile Materials Sheila Shahidi and Jakub Wiener Additional information is available at the end of the chapter http://dx.doi.org/10.5772/63731

Abstract Irradiation processes have several commercial applications, in the coatinμ oλ metals, plastics, and μlass, in printinμ, wood λinishinμ, λilm and plastic cross-linkinμ, and in the λields oλ adhesive and electrical insulations. The advantaμes oλ this technoloμy are well known. Radiation treatment on λabric and μarments can add value in coloration, antiλeltinμ, printinμ, and coatinμ. In this chapter, diλλerent irradiation methods such as plasma, electron beam, laser, ion implantation, microwave, μamma, and ablation are described, and the eλλects oλ these process in textile industry as a λinishinμ method are discussed and compared with conventional methods. Keywords: Irradiation, Fabric, Textile, Material, Finishinμ

. Introduction The advancement oλ technoloμy in the textile market has led scientists and researchers to develop novel λinishes to add hiμh value on deλerent textile materials. It was a new window λor researchers to advent and explore new research λields which include μeotextiles, λlame retardant textiles, insect repellent textiles, aroma textiles, medical textiles, smart textiles, antibacterial textiles, and nanotextiles, etc. Recent developments in the textile industry are mainly λocused on physical and chemical modiλications on surλace oλ λibers and λabrics. Diλλerent chemical and bioloμical methods have been used electively to improve or impart permanent λunctional properties on the surλace oλ textile materials. However, some oλ these chemicals are toxic and sometimes expensive [ ].

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“lternatively, radiation technoloμy involvinμ low enerμy use, no chemicals, ease to handlinμ, and hiμh treatment speed can modiλy the surλace oλ textiles and improve dye uptake, printinμ, λastness properties, adhesion oλ coatinμs, and adsorption oλ used chemicals. In this chapter the eλλect oλ ultraviolet UV , μamma, plasma, laser, microwave, electron beam, ion beam, ultrasonic on surλace, chemical, and physical and mechanical properties oλ textile materials is λully discussed.

. UV irradiation and its application in textile industry One oλ the eλλective and economical methods oλ surλace modiλication λor both natural and synthetic polymers is UV irradiation. Excitation and dissociation oλ the polymeric molecules take place durinμ exposinμ the surλace to the UV treatment, which is known as a photosensi‐ tized oxidation process. The color depth oλ the polylactide PL“ and polyethylene terephthalate PET λabrics has been increased by the UV irradiation. This increase in the depth oλ dyeinμ is believed to be due to the surλace rouμheninμ oλ the λabrics produced by the UV [ ]. “ccordinμ to previous research work which has been done, the prepared thin λilm polyamide nanoλiltration membranes were modiλied by acrylic acid ““ and UV irradiation. The eλλect oλ UV-irradiation time and addition oλ ““ on the perλormance and morpholoμy oλ nanoλil‐ tration membranes were investiμated. The obtained membranes illustrate the ability λor rejection oλ Na SO and siμniλicant properties λor separation oλ divalent ions λrom monovalent ions [ ]. In recent years, many methods have been reported λor modiλyinμ PET λabric to be hydrophilic. Diλλerent types oλ chemical auxiliaries can be used λor this purpose. However, the hydrophi‐ licity oλ the treated PET surλace is not durable because the coated hydrophilic material easily dissolves durinμ repeated washes. Photo-chemical reactions and photophysical processes are μaininμ attention as techniques λor modiλyinμ the surλace oλ PET λabrics [ ]. UV irradiation and treatment with nano-TiO , H O , and NaOH increased the hydrophilicity oλ PET λabric, with an irradiation time oλ min makinμ the λabric nearly wettable and an irradiation time oλ min makinμ the λabric superhydrophilic. The μreatest and most durable wettability results were obtained aλter min oλ UV irradiation combined with μ/L nanoTiO , μ/L H O , and μ/L NaOH treatment. The excellent mechanical and physical properties oλ PET λabric were retained aλter modiλication, althouμh the breakinμ strenμth and elonμation were sliμhtly reduced. The induced hydrophilicity oλ the PET λabric can be considered permanent because the surλace oλ the PET λabric was chemically modiλied with the introduction oλ hydrophilic μroups [ ]. In the other research, a new technique has been presented to μraλt sulλonic μroups at the surλace oλ PET λabric, which is based on UVC treatment with SO μaseous molecule. These modiλica‐ tions improved the hydrophilic character oλ PET λabric surλace and consequently its dyinμ

Radiation Effects in Textile Materials http://dx.doi.org/10.5772/63731

ability. The Schematic oλ system is shown in Figure . The air λlow containinμ λuminμ SO molecules is injected into the vessel between which is composed oλ an UVC lamp and the λabric to be treated. The UVC lamp emits intense and nearly monochromatic liμht nm . In λact, the UVC lamp emits kJ mol− per photon, which allows the PET λibers λunctionalization without damaμinμ their bulk properties. Sulλonic SOH μroups can be introduced into aromatic compounds throuμh an electrophilic substitution reaction. Such a reaction is reλerred as sulλonation [ ].

Figure . UVC treatment device [ ].

The results reported in the other research demonstrate that the UVC nm irradiation method under a stream oλ μaseous Cl has the potential to μraλt PET textile λabrics. This technique has many advantaμes, such as easy handlinμ, and it is a cheap, solvent-λree contin‐ uous process without chanμinμ the bulk properties. The medication involves only a λew nanometres oλ the surλace. Several analytical techniques have conλirmed that surλace chlori‐ nation has occurred. Scanninμ Electron Microscope SEM analyses showed that the chlorina‐ tion only occurred at the surλace oλ the λibers without chanμinμ the bulk oλ λibers. The Diλλerential scanninμ calorimetry DSC thermoμrams indicated that the thermal characteris‐ tics oλ the PET λabrics were maintained. X-ray photoelectron spectroscopy XPS also showed the presence oλ Cl atoms in the upper molecular layers oλ the surλace. The aλλinity oλ modiλied λabrics to cationic dyes is more than untreated samples [ ]. For a lonμ time, the textile industry has been searchinμ λor a rapid way to modiλy textile polymer surλaces. Obtaininμ μood bondinμ between two dissimilar materials is critical λor several aspects in textile λinishes processinμ. “dhesion between PET and Tuλtane Thermo‐ plastic Polyurethane TPU Film was improved by μraλtinμ NCO μroups onto the PET surλace usinμ UV irradiation process by Donμ Liu and his coworkers [ ].

. Gamma irradiation on textile fabrics Gamma rays are hiμh-enerμy electromaμnetic radiations havinμ enerμies above keV and wavelenμths less than picometers. Surλace modiλication oλ textiles usinμ μamma ray is one oλ the promisinμ methods.

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The excellent mechanical properties, heat and oxidation resistance, and environmental stabilities make carbon λiber λabrics ideal reinλorcinμ materials in the advanced composite λields, such as solar panel oλ space station and electric vehicle body. “ll these excellent properties depend larμely on the interλacial adhesion which λinally aλλects the overall property oλ the resultinμ composites. Recently, radiation-induced μraλtinμ has been extensively applied as a competitive methodoloμy to develop new λunctional materials. “n easy method to evenly λunctionalize the λabric surλaces by γ-ray irradiation μraλtinμ was reported. This novel technique is simple, μreen, and versatile. The λunctionalization was much more uniλorm compared with the traditional electrochemical method. The interλacial strenμth oλ the compo‐ sites had a dramatic increase [ ]. Presently, polymeric membranes are extensively employed in the λield oλ biomedical materials contactinμ with blood. Sulλonated polypropylene nonwoven λabric PPNWF has been successλully prepared via μamma-ray preirradiation-induced μraλt polymerization oλ sodium styrenesulλonate SSS and acrylamide ““m by li et al Figure .

Figure . Schematic diaμram oλ preparinμ sulλonated PP NWF via μamma-ray preirradiation method [ ].

Gamma ray preirradiation-induced coμraλt polymerization has been extensively applied to modiλied polymer materials because oλ its simple procedure and even μraλtinμ. “crylonitrile “N has been widely used in the modiλication oλ materials and an amidoxime μroup can be obtained by λurther chemical treatments λrom the nitrile μroup to increase adsorption eλλi‐ ciency λor heavy ions. In a research that has been done in by Liu and his coworkers, a preirradiation-induced emulsion coμraλt polymerization method was used to introduce “N and ““ onto a PE nonwoven λabric. The use oλ ““ is meant to improve the hydrophilicity oλ the modiλied λabric. The modiλied nonwoven λabric is ready λor λurther amidoximation to the application oλ heavy metal ion extraction [ ]. In the other research, SSS was μraλted onto PPNWF via γ-ray coirradiation method with the existence oλ N-vinyl- -pyrrolidone. The modiλied PPNWFs presented μood blood compatibil‐ ity, such as lower hemolysis rate and lower platelet adhesion. ”esides, the modiλied PPNWFs prolonμed the clottinμ time and presented excellent anticoaμulant eλλect [ ]. The textile industries are one oλ the major sources oλ water pollution in terms oλ releasinμ hiμhly colored waste stream in surλace water bodies. The wastewater μenerated in textile

Radiation Effects in Textile Materials http://dx.doi.org/10.5772/63731

processinμ plants is contaminated with toxic synthetic colorants and various perilous chemicals. The main objectives oλ the study by ”huiyan et al. were to deμrade the dye molecules and orμanic pollutants oλ textile wastewater by usinμ μamma irradiation λollowed by the investiμation oλ physicochemical parameters oλ the irradiated water as well as lookinμ into the scope λor usinμ treated wastewater λor irriμation and dyeinμ purposes. The wastewater samples were submitted to Cobalt- μamma radiation source. The irradiated wastewater was λound to be recyclable in textile wet processinμ and reusable λor irriμation purposes [ , ]. The presence oλ toxic metals and pathoμenetic microbes in drinkinμ water is a potential health risk. Consequently, numerous investiμations have been carried out on the λunctionalized polymer membrane with “μNPs as eλλective antimicrobial aμents λor water treatment. Unλortunately, the “μNPs were commonly inert with polymer surλaces so that silver releases into water λiltrate in an overdose compared to the permitted limit oλ standard at maximum oλ . mμ/L, accordinμ to the US Environmental Protection “μency EP“ and World Health Orμanization WHO . “ new method to immobilize “μNPs onto the acrylic μraλted polyethylene nonwoven PE λabric by μamma Co- irradiation λor drinkinμ water treatment has been described in . The PE λabric pieces were treated by a mixture oλ acetone/H O solution and dried beλore irradiation. The PE λabric samples were irradiated at the required doses up to kGy by γ ray λrom Co- source. Thereaλter, the μraλt reactions were carried out at ∼ °C in a λlask con‐ taininμ μ preirradiated PE, . μ Mohr’s salt and ““ with concentrations oλ – % v/v in ml aqueous solution. The PE-μ-P““c samples were soaked overniμht at room temperature in “μ NPs colloidal solutions and then squeezed to remove the excess “μ NPs, rinsed with pure water and dried in an oven at C λor h. The dried λabrics were then annealed at C λor h λor esteriλication oλ –COOH μroup oλ P““c with –OH μroup oλ Polyvinyl alcohol PV“ . The prepared λabrics contained about , ppm “μ NPs showinμ stronμ bactericidal eλλiciency aμainst Escherichia coli. ”ased on the stronμ bactericidal eλλiciency and under permitted limit oλ silver release into water λiltrate, PE-μ P““c/“μ NPs λabrics can be used λor the treatment oλ drinkinμ water. “lso, this kind oλ λilters can be used in air cleaners and have other applications [ ]. In the other research, the silver ions have been reduced eλλectively by μamma irradiation and immobilized on the cotton λabrics by in situ synthesis. The “μ NPs content deposited on the λabrics was oλ mμ/kμ, when the λabric sample was irradiated in . mM “μ NO and . % chitosan solution at the dose oλ . kGy at °C. “ntibacterial eλλicacy oλ the “μ NPs λabrics aλter washinμ cycles oλ washinμ was about . % λor Staphylococcus aureus and E. coli. The “μNPs/cotton λabrics washinμ λrom to cycles were innoxious to skin k = . These results conλirm that μamma irradiation oλ cotton λabrics in the presence oλ “μNO and chitosan solution is a promisinμ approach λor preparation oλ stable, saλe, and eλλicacious antibacterial λabrics [ ]. In the past decades, the materials with hiμh water and oil repellency have attracted much attention λrom researchers and industries. The perλluoroalkyl phosphate acrylates have been

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μraλted onto a cotton λabric via μamma-ray irradiation to improve the hydrophobic and oleophobic properties.

Figure . Photoμraphs oλ water and sunλlower oil drops on the μraλted sample [

].

The results show that the λabric became hiμhly hydrophobic and oleophobic with the contact o o anμles oλ above and λor water and sunλlower oil, respectively Figure [ ]. In the other research, a novel coatinμ λormulation λor improvinμ the UV protection property on cotton, PET, and cotton/PET λabrics was prepared, and μamma rays were applied λor surλace curinμ. “luminum potassium sulλate “lum was used individually and in binary coat with Zinc Oxide ZnO , to induce the UV-blockinμ properties [ ].

. Microwave applications in textile industry Microwaves comprise electromaμnetic radiation in the λrequency ranμe oλ MHz– GHz. “s the polar or charμed particles in a reaction medium λail to aliμn themselves as λast as the direction oλ the electric λield oλ microwaves chanμes, λriction is created to heat the medium [ ]. They can penetrate into a material and heat the deep layers oλ the material stronμly when they release their enerμy. Microwave irradiation oλλers a number oλ advantaμes over conventional heatinμ methods, includinμ usinμ less enerμy, oλλerinμ a hiμher heatinμ rate, and oλλerinμ the ability to more quickly start and stop heatinμ. Sulλonatinμ a PET λabric by dilute sulλuric acid and microwave irradiation has been λound to produce a super-hydrophilic PET λabric, and the λibers sustained minimal damaμe. PET λabric has been immersed in H SO solutions with diλλerent concentrations at room temperature λor min. PET λabric samples were then dried at °C λor min and then irradiated with microwaves at MHz usinμ a commercial W microwave oven λor min. The SEM imaμes oλ both

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untreated and treated PET are shown in Figure . The surλaces oλ the oriμinal and the modiλied PET λibers are all smooth.

Figure . SEM imaμes × λ PET λibers modiλied by

and × oλ a, b the oriμinal PET λibers c, d PET λibers modiλied by μ/L H SO and μ, h PET λibers modiλied by μ/L [ ].

μ/L H SO

e,

Microwave modiλication process is quick and inexpensive. Thereλore, the modiλication process could be used in a wide ranμe oλ applications [ ]. Polyamide P“ is one oλ the most abundantly used λabric in many areas attributed to its low cost, resistance to shrinkaμe, abrasion, etc. However, its combustibility and serious drippinμ produced durinμ combustion cannot meet industrial and civil requirements in many cases. Zhao et al. researched the eλλorts on surλace modiλication oλ P“ λabric by microwaveinduced μraλtinμ with -hydroxyethyl methacrylate HEM“ . The μraλtinμ reaction was undertaken in water solution to decrease the damaμe oλ λabric. The hydrophilicity, drippinμ tendency, and mechanical properties oλ μraλted samples have been siμniλicantly improved. However, the sliμht chanμe oλ limitinμ oxyμen index LOI values and hiμh damaμed lenμth durinμ burninμ cannot meet the λlame retardant requirements in many λields [ ]. Microwave MW enerμy which is used in dyinμ oλ various types oλ textile staple and λixation processes has brouμht positive results. Microwave irradiation increases the diλλusion oλ dye molecules in dyeinμ process when applied to both synthetic and natural λibers. It is also used in preλinishinμ oλ silk yarns. In addition MW enerμy is accepted as more eλλicient than conventional methods λor cotton λabric λinishinμ, dryinμ, and curinμ processes, durable press λinishinμ, incombustibility, water and oil repellent λinishinμ [ ].

. Ultrasonic in textile industry Ultrasound technoloμy is amonμ the irradiation technoloμies whose applications in diλλerent branches oλ industries have soared in recent years.

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Ultrasound technoloμy has been extensively used λor detectinμ deλects in a larμe variety oλ industrial components and materials. Usinμ ultrasound waves throuμh the air is not the λirst choice due to the hiμh impedance mismatch between air and most oλ transducer and compo‐ nent materials. “s a result, a hiμher impedance substance is employed as a couplant to optimize the acoustic enerμy transλer to the sample, λor example, water or a couplinμ μel. Nevertheless, in some processes, it is not allowed to use a wet couplinμ, which makes room λor a speciλic cateμory oλ applications usually named as noncontact or airborne ultrasound. “n example oλ this is the inspection oλ textile μoods, where a wet couplinμ substance could deμrade the λabric and/or slow the manuλacturinμ process. Several previous investiμations have shown that ultrasonic technoloμy enhances mass transλer durinμ some textile processinμ steps such as desizinμ, scourinμ, bleachinμ, mercerizinμ, and dyeinμ oλ natural λabrics. Pazos-Ospina et al. in presents a desiμn methodoloμy λor halλ-curved airborne ultrasonic arrays based in cellular λerroelectret λilm. The μeometry oλ the array proposed allows them λocus naturally in the vertical plane and electronically in the horizontal one, obtaininμ similar spatial resolution in both directions. Theoretical predictions and simulated results were validated with a developed array prototype desiμned to operate at λrequencies between kHz and kHz. The potential oλ the device was shown by inspectinμ diλλerent textile samples in transmission mode. This multi-transducer desiμn is a low-cost alternative to the use oλ composite D arrays in noncontact ultrasonic inspections [ ]. Cleaninμ oλ materials is one oλ the most important applications oλ ultrasound. However, the use oλ ultrasonic enerμy λor textile washinμ has been searched many years without achievinμ commercial development. The cleaninμ action oλ ultrasonic enerμy is due to cavitations. The implosion oλ vapor bubbles inside the cleaninμ auxiliaries and near the surλace to be cleaned imposes such stress on the surλace that erodes the contaminant and removes the impurities. On the other hand, stable cavitations, may also cause the dispersion oλ the particles oλ contaminant removed λrom the surλace.

Figure . ”asic scheme oλ the ultrasonic process [ ].

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“n ultrasonic system λor the continuous washinμ oλ textiles in liquid layers based on a procedure has been desiμned and constructed by Galleμo-Juarez et al. in . The system incorporates, as the main part, special plate transducers capable λor hiμh-power operation without the interaction oλ perturbinμ undesired vibration modes. This system has shown very μood washinμ behavior either with the laboratory or the semiindustrial set-up Figure [ ]. Recently, attempts have been made to use acoustic cavitation λor washinμ textiles. Ultrasonic cleaninμ has been widely employed to remove submicron-sized contaminant particles adherinμ to solid substrates e.μ., photo masks and waλers in semiconductor industry. Ultrasonic waves travelinμ in a liquid result in cavitation and thus produce bubbles. The bubbles exhibit rich dynamic behaviors such as translation, oscillation, μrowth, and collapse in response to the varyinμ acoustic pressure [ ]. In the recent decade, the application oλ ultrasonic irradiation as an advanced oxidation process has attracted much attention because oλ the μeneration oλ hiμh amounts oλ •OH radicals due to the ultrasonic cavitation. The ultrasonic waves result in the rapid μrowth and subsequently, collapse oλ the cavitation bubbles, which produces extremely hiμh pressure up to atm and temperature as hiμh as K in the bubbles. The hiμh temperature, toμether with the hiμh pressure, named hot spots€ leads to the μeneration oλ •OH within the μas–liquid transition zone near the bubbles and bulk solution as a result oλ the water dissociation. It has been demonstrated that the catalytically enhanced ultrasonic irradiation based on the appli‐ cation oλ semiconductors, known as sonocatalysis, has hiμher deμradation eλλiciency and lower processinμ time than that oλ sonication alone. Darvishi Cheshmeh Soltani et al. in used a porous clay-like support with unique charac‐ teristics λor the synthesis and immobilization oλ ZnO nanostructures to be used as a sonoca‐ talyst λor the sonocatalytic decolorization oλ methylene blue M” dye in the aqueous phase. They concluded that the sonocatalytic activity oλ ZnO–biosilica nanocomposite . % was hiμher than that oλ pure ZnO nanostructures . % . Increasinμ the initial pH λrom to led to increasinμ the color removal λrom . % to . %, respectively. Increasinμ the sonocatalyst dosaμe λrom . to . μ/L resulted in increasinμ the color removal. They also concluded that the ZnO–biosilica nanocomposite can be a suitable sonocatalyst λor the sonocatalytic decolor‐ ization oλ colored solutions with hiμh reusability potential and cost-eλλiciency [ ]. “s an alternative to the existinμ λinishinμ technoloμies, a λacile one-step sonochemical route has been suμμested λor uniλorm deposition oλ inorμanic nanoparticles on the surλace oλ solid substrates, includinμ textiles. The antimicrobial λinishinμ is very important λor medical textiles, decreasinμ the risk oλ hospital-acquired inλections. Petkova et al. in report a simultaneous sonochemical/enzymatic process λor durable antibacterial coatinμ oλ cotton with zinc oxide nanoparticles ZnO NPs . The novel technoloμy μoes beyond λirst enzymatic preactivation oλ the λabrics and subsequent sonochemical nanocoatinμ and is desiμned to produce ready-to-use€ antibacterial medical textiles in a sinμle step.

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“ multilayer coatinμ oλ uniλormly dispersed NPs was obtained in the process. The pretreat‐ ment with enzymes causes better adhesion oλ the ZnO NPs on the surλace oλ cotton λabrics. The NPs-coated cotton λabrics inhibited the μrowth oλ S. aureus and E. coli, respectively, by % and %[ ] Textile dyeinμ assisted by ultrasonic enerμy has attained a μreater interest in recent years. Ultrasonic-assisted dyeinμ oλ cellulosic λibers has already proved to be a better choice amonμ conventional dyeinμ by many researchers. Khatri et al. in reported ultrasonic dyeinμ oλ nanoλibers. They chose cellulose nanoλibers and dyed with two reactive dyes, CI reactive black and CI reactive red . Results revealed that the ultrasonic dyeinμ produced hiμher color yield K/S values than the conventional dyeinμ. The color λastness test results depicted μood dye λixation. “lso they have reported that ultrasonic enerμy durinμ dyeinμ does not aλλect surλace morpholoμy oλ nanoλibers. The results conclude successλul dyeinμ oλ cellulose nanoλibers usinμ ultrasonic enerμy with better color yield and color λastness results than conventional dyeinμ [ ].

. Laser in surface modification of polymer and fabrics Laser modiλication on material surλace is one oλ the most studied technoloμies. It has been shown that various materials modiλied by laser irradiation oλten exhibit physical and chemical chanμes in the material’s surλace. In μeneral, laser irradiation could not aλλect the bulk properties oλ a polymer due to its low penetration depth Figure [ , ].

Figure . Surλace structure oλ polyester λiber under hiμh λluence

pulses at

mJ/cm [

].

Radiation Effects in Textile Materials http://dx.doi.org/10.5772/63731

In the research which has been done by ”ahtyari, the eλλect oλ CO laser treatment on the dyeability oλ polyimide λabrics reveals that, λollowinμ laser treatment, the dyeability oλ polyamide increased siμniλicantly. This is accompanied by a siμniλicant burstinμ strenμth loss. It has been observed that, as the laser modiλication oλ the λabric was carried out with low intensity, the concentration oλ λree amino μroups, which are necessary durinμ dyeinμ with acid and reactive dyes, increased [ ]. The modiλication induced in PL“ by the “rF excimer laser radiation has been investiμated by Rytlewski et al. It was λound that the surλace enerμy chanμe was aλλected by surλace oxidation as well as by surλace rouμhness. “rF laser surλace treatment can be an eλλective way oλ improvinμ PL“ adhesion properties [ ]. “nother article λocused on the development oλ a laser pretreatment method λor μlass-λibrereinλorced polypropylene surλaces λor industrial applications. The aim oλ this research is to create a surλace λor bondinμ polypropylene which adheres very poorly to most oλ the materials and λorms to the matrix material λor plastic composites [ ]. On the other hand, as is known, the laser is a source oλ enerμy which can be used λor irradiation oλ diλλerent substrates and its power and intensity can be easily controlled. ”y usinμ laser, it is possible to cut a μreat variety oλ material λrom metal to λabric. “lso it would be possible to transλer certain desiμns onto the surλace oλ textile material by chanμinμ the dye molecules in the λabric and chanμinμ the color quality values by laser irradiation oλ λabrics at reduced intensity Figure [ ].

Figure . Some examples oλ denim trousers desiμned by laser beam method [ ].

The CO laser-thinninμ method has been applied to the PET λiber to prepare the PET nonwoven λabric without usinμ the solvent by Suzuki et al.

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The obtained nonwoven λabric was made oλ continues microλibers with a uniλorm diameter without a droplet. The laser-thinninμ method has been λound to be eλλective λor producinμ other nonwoven λabrics such as poly L-lactic acid and poly μlycolic acid . The schematic oλ setup is shown in Figure [ ].

Figure . CO laser-thinninμ apparatus used λor web λormation [

].

CO laser treatment was used as a novel method λor creatinμ antibacterial properties on μlass mat by Wiener et al. in . Various types oλ metallic salts such as CuO, ZnO, and “μNO were applied on surλace oλ μlass mat and irradiated with the laser liμht beam μs . Metal particles were deposited on the surλace oλ samples. The antibacterial properties oλ the λabrics were connected with the presence oλ metal particles on their surλace. Wiener et al. concluded that the chanμe in properties induced by laser can eλλect an improvement in certain textile products [ ]. Glass λiber mat surλace modiλications were carried out usinμ CO laser. The μeometry oλ the experiment is visualized in Figure . In the laser tube produces IR laser beam . In the direction oλ laser beam, computer-adjusted mirror is located which determined the positron oλ irradiated place on μlass λiber mat . The temperature oλ the μlass λiber mat on its irradiated side cannot be measured due to hiμh intensity oλ IR laser beam. So only the temperature oλ back side oλ μlass λiber mat was estimated by inλrared thermometer . Laser liμht treatment

Radiation Effects in Textile Materials http://dx.doi.org/10.5772/63731

oλ μlass λiber resulted in interestinμ properties based on the mechanical properties, such as strenμth, modulus, and elonμation oλ the μlass λiber mat, the permeability, morpholoμical properties, and the thickness. Wiener et al. in concluded that by increasinμ the laser intensity, the strenμth and modulus oλ the mat decrease. ”ut in the case oλ laser cyclinμ treatment, the mechanical properties are improved. We observed that laser treatment causes increase oλ porosity and better air perme‐ ability [ ].

Figure . Schematic view oλ the laser treatment oλ μlass λiber and temperature measurement [

].

. Plasma and its application in textile industry Plasma technique can have very important eλλects on the properties oλ textile materials. Diλλerent types oλ plasma μases have diλλerent eλλects on the surλaces oλ textiles. Plasma has many potential λor the activation and λunctionalization oλ textile materials. Plasma technoloμy is slow but steady in the industrial revolution. Surλace modiλication oλ textiles cannot replace all wet processes, but it can be a viable pretreatment, which can provide plenty oλ environ‐ mental and economical beneλits. Thereλore, textile industry should consider the concept oλ hiμher initial investments in equipment that will be paid oλλ quickly with respect to environ‐ ment-related savinμs and the proλit oλ the sale oλ hiμh value-added products [ – ]. Improvinμ the λastness properties and antibacterial activity oλ dyed cotton samples was studied by Shahidi in . In her research, λirst cotton λabrics were dyed with various types oλ dyestuλλs such as Direct, Vat, and Reactive. Then prepared samples were sputtered usinμ plasma sputterinμ system λor s by silver and copper. For deposition oλ metal nano layer on the surλace oλ samples, DC maμnetron putterinμ system was used. Samples were placed on the anode. ”y attackinμ active ions, radicals, and electrons, the cathode particles were scattered.

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Silver or copper particles were deposited on the surλace oλ cotton samples, and throuμh incorporation oλ metal nano particles on λabric surλaces, the antibacterial has been developed. It can be concluded that sputterinμ technique can be a novel method λor improvinμ the λastness properties oλ dyed cotton samples [ ]. DC maμnetron sputterinμ system λor creatinμ antibacterial and ultraviolet protective cotton λabrics has been used by Shahidi et al. in . “ silver anode and cathode were used. Silver particles were deposited on the both sides oλ cotton samples, and the antibacterial property has been developed, throuμh sputterinμ oλ silver particles on λabric surλaces. Treated cotton λabrics had an excellent UV-blockinμ property. “ccordinμ to the standard, the treated cotton λabric can claim to be a UV Protective product.€ They concluded that the chanμe in properties induced by plasma can eλλect an improvement in certain textile products [ ]. Conventional wet treatment in textile industry involves hiμh consumption and pollution oλ water resources. Wastewater processinμ costs are hiμh, and dryinμ the wetted λibers is enerμy-, time-, and cost-intensive. So the textile industry has a μreat interest in alternative dry processes. Low temperature plasma treatment is a dry and ecoλriendly technoloμy which has been widely used to modiλy the chemical and topoμraphical properties oλ polymers and textiles surλace. The application oλ plasma technoloμies as a pretreatment and λinishinμ process λor textiles has become very popular because this surλace modiλication method chanμes the outermost layer oλ the substrate without alterinμ the bulk properties. Low-pressure plasma treatments are known to induce physical and chemical surλace chanμes in textile λibers throuμh several concurrent processes activation, etchinμ, μraλtinμ chemical λunctional μroups, and crosslinkinμ . Girmoldi et al., in , perλormed atmospheric pressure plasma treatments oλ pure cashmere and wool/cashmere textiles with a dielectric barrier discharμe D”D in humid air air/water vapor mixtures . Their analyses revealed a surλace oxidation oλ the treated λabrics, which enhances their surλace wettability with minor etchinμ eλλects, an essential λeature λor the maintenance oλ the textile soλtness [ ]. “ir plasma treatment can modiλy the physical and chemical properties oλ the surλace, and it causes to increase the hydrophilic character oλ a material. The production oλ new textile products λor cosmetic applications requires pretreatment on the surλace oλ λabrics. In this kind oλ application, the textile must have some orμanoleptic and aesthetic properties which require the use oλ soλteners. Surλace modiλication oλ the P“ λibers by low temperature plasma has been studied by Labay et al. in . Corona plasma treatment has been investiμated to achieve surλace modiλication in the λirst nanometers oλ polymer λibers surλace in order to modulate the incorporation and the release oλ caλλeine. Plasma treatment improved the caλλeine release [ ]. Polyester λiber is one oλ the most important materials λor textile manuλacturinμ. However, the conventional antistatic λinishinμ processes λor polyester involve numerous enerμies and chemicals, with correspondinμ environmental pollution. The synerμetic eλλects oλ lowtemperature oxyμen plasma P and N,O-carboxymethyl chitosan N treatments on the antistatic and antibacterial properties oλ polyester λabrics were investiμated by Liu et al. in

Radiation Effects in Textile Materials http://dx.doi.org/10.5772/63731

. They concluded that all the treated polyester λabrics had no obviously antibacterial eλλect on E. coli Gram-neμative . Their λindinμs indicated that the proposed process can provide μood antistatic perλormance λor polyester λabrics with a minimum oλ pollution [ ]. In , pure cashmere and wool/nylon textiles were modiλied by means oλ an atmospheric pressure plasma treatment with a D”D in humid air λollowed by a λinishinμ process with a λluorocarbon resin by Zanini et al. Their result indicated a hiμher amount oλ λluorocarbon resin on the surλace oλ the λabric which was plasma treated beλore the λinishinμ process and a more uniλorm coveraμe oλ the λibers oλ this textile. They concluded that the hydrophilic character oλ the plasma-activated λabric leads to a hiμher adsorption oλ the water-based dispersion that contain the λluorocarbon resin and limit the de-wettinμ phenomenon oλ the λibers durinμ the dryinμ step. “ll these results hiμhliμht the importance oλ the plasma activation step to enhance the hydro- and the oleo-repellent properties oλ the modiλied λabrics, as assessed by diλλerent analyses water contact anμle, standard tests λor hydro- and oleo-repellence, and water adsorption isotherms [ ]. Textile industry wastewater has larμe amounts oλ orμanic dyes that are resistant to the bioloμical methods. Moreover, other physical and chemical processes such as adsorption and coaμulation merely transλer contaminants to a secondary phase and require more treatment. Fenton and sonication processes are simple and eλλicient methods that are applied λor the mineralization oλ various contaminants λrom polluted water sources. The plasma-treated pyrite PTP nanostructures were prepared λrom natural pyrite NP utilizinμ arμon plasma due to its sputterinμ and cleaninμ eλλects resultinμ in more active surλace area by Khataee et al. in . They reported that, environmentally λriendly plasma modiλication oλ the NP, in situ production oλ H O and OH radicals, low-leached iron concentration and repeated reusability at the milder pH are the siμniλicant beneλits oλ the PTP utilization. The siμniλicant advantaμes oλ the stable PTP are not needed λor addinμ oλ H O , low-leached iron amount, and application at the milder pH [ ].

Figure

. Schematic diaμram oλ the μlow discharμe plasma system used in Khataee et al. study

[ ].

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. Conclusion In textile industry, the surλace modiλication oλ λibers is correlated to surλace properties such as water repellence and adhesion. In the recent years, there have been many researches in developinμ surλace modiλication methods to improve the surλace properties oλ textile materials in order to develop new market products. Several surλace modiλication methods are employed. The irradiation treatments have been ahead oλ recoμnition as a surλace modiλication technique. Much attention has been paid to treatinμ the surλaces oλ materials with irradiation methods in the past λew decades. In μeneral, treatinμ the surλace oλ a material with irradiation methods can cause physical and chemical chanμes to occur at the surλace but aλλect the bulk properties oλ the material little.

Author details Sheila Shahidi * and Jakub Wiener *“ddress all correspondence to [email protected] Department oλ Textile, “rak ”ranch, Islamic “zad University, “rak, Iran Department oλ Textile Chemistry, Faculty oλ Textile, Technical University oλ Liberec, Lib‐ erec, Czech Republic

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[ ] Sulλonation oλ polyester λabrics by μaseous sulλur oxide activated by UV irradiation, ”essem Kordoμhli, Ramzi Khiari, Mohamed Farouk Mhenni, Mohamed Naceur ”elμacem, Faouzi Sakli, “ppl Surλ Sc – . [ ] UV irradiation-assisted μraλtinμ oλ poly ethylene terephthalate Fabrics, ”essem Kordoμhli, Ramzi Khiari, Hatem Dhaouadi, Mohamed Naceur ”elμacem, Mohamed Farouk Mhenni, Faouzi Sakli, Colloids and Surλaces “ Physicochem. Enμ. “spects – . [ ] UV-assisted surλace modiλication oλ PET λiber λor adhesion improvement, Xianμ-Donμ Liu, De-Kun Shenμ, Xiu-Mei Gao, Tonμ-”inμ Li, Yu-Minμ Yanμ, “ppl Surλ Sc – . [ ] Uniλorm modiλication oλ carbon λibers in hiμh density λabric by X-ray irradiation μraλtinμ, Fenμ Zhao, Yudonμ Huanμ, Mat Lett – . [ ] In vitro hemocompatibility oλ sulλonated polypropylene non-woven λabric prepared via a λacile μama-ray pre-irradiation μraλtinμ method, Ronμ Li, Guozhonμ Wu, Yin Ye, “ppl Surλ Sc – . [

] Pre-irradiation induced emulsion co-μraλt polymerization oλ acrylonitrile and acrylic acid onto a polyethylene nonwoven λabric, Hanzhou Liu, Minμ Yu, Honμjuan Ma, Ziqianμ Wanμ, Linλan Li, Jinμye Li, Radiat Phys Chem – .

[

] Gamma-ray co-irradiation induced μraλt polymerization oλ NVP and SSS onto poly‐ propylene non-woven λabric and its blood compatibility, Ronμ Li, Henμdonμ Wanμ, Wenλenμ Wanμ, Yin Ye, Radiat Phys Chem – .

[

] Scope oλ reusinμ and recyclinμ the textile wastewater aλter treatment with μamma radiation, M.“. Rahman ”huiyan, M. Mizanur Rahman, “bu Shaid, Mubarak “. Khan, M.M. ”ashar, J Clean Prod –e .

[

] Cytotoxicity and mutaμenicity evaluation oλ μamma radiation and Hydroμen peroxide treated textile eλλluents usinμ bioassays, Munawar Iqbal, Jan Nisar, J Environ Chem Enμ – .

[

] Study oλ incorporation oλ silver nanoparticles onto PE-μ-P““c nonwoven λabric by μama-irradiation λor water treatment, Danμ Van Phu, Le “nh Quoc, Nμuyen Nμoc Duy, Nμuyen Quoc Hien, Radiat Phys Chem – .

[

] Gamma irradiation oλ cotton λabrics in “μNO solution λor preparation oλ antibacterial λabrics, Truonμ Thi Hanh, Danμ Van Phu, Nμuyen Thi Thu, Le “nh Quoc, Do Nu”ich Duyen, Nμuyen Quoc Hien, Carbohyd Polym – .

[

] Cotton λabric modiλication λor impartinμ hiμh water and oil repellency usinμ perλluor‐ oalkyl phosphate acrylate via μ-ray-induced μraλtinμ, Hui Miao, Fenλen ”ao, Lian‐ μlianμ Chenμ, Wenλanμ Shi, Radiat Phys Chem – .

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[

] Novel UV-protective λormulations λor cotton, PET λabrics and their blend utilizinμ irradiation technique, Maμed H. Zohdy, Mamdouh ”. El Hossamy, “bdel Wahab M. El-Naμμar “beer I. Fathalla, Nisreen M. “li, Eur Polym J – .

[

] Use oλ microwave irradiation in the μraλtinμ modiλication oλ the polysaccharides.–“ review, V. Sinμh, P. Kumar, R. Sanμhi, Proμ Polym Sci – .

[

] Facile preparation oλ super-hydrophilic poly ethylene terephthalate λabric usinμ Dilute sulλuric acid under microwave irradiation, Fanμ Xu, Guanμxian Zhanμ, Fenμxiu Zhanμ, Yuansonμ Zhanμ, “ppl Surλ Sc – .

[

] Surλace modiλication oλ polyamide λabric by microwave induced μraλtinμ with hydroxyethyl methacrylate, Qian Zhao, Xiaoyu Gu, Shenμ Zhanμ, Minμzhe Donμ, Penμ Jianμ, Zhonμwu Hu, Surλ Coat Tech – .

[

] Usaμe oλ Microwave Enerμy in Turkish Textile Production Sector, ”anu Yeşim ”(y(‐ kakinci, Enerμy Procedia – .

[

] New dual-λocalization λerroelectret-based array λor air-coupled ultrasonic inspection oλ textiles, Pazos-Ospina J.F., EaloJ.L., Camacho J. NDT&E Int – .

[

] Ultrasonic system λor continuous washinμ oλ textiles in liquid layers, Juan “. GalleμoJuarez, Enrique Riera, Victor “costa, Germ‫ل‬n Rodriμuez, “lλonso ”lanco, Ultrason Sonochem – .

[

] Ultrasonic washinμ oλ textiles, Junhee Choi, Tae-Honμ Kim, Ho-Younμ Kim, Wonjunμ Kim, Ultrason Sonochem xxx xxx–xxx.

[

] Ultrasonically induced ZnO–biosilica nanocomposite λor deμradation oλ a textile dye in aqueous phase, Reza Darvishi Cheshmeh Soltani, Sahand Jorλi, Hojjatallah Ramezani c, Sudabeh Purλadakari, Ultrason Sonochem – .

[

] Simultaneous sonochemical-enzymatic coatinμ oλ medical textiles with antibacterial ZnO nanoparticles, Petya Petkova, “ntonio Francesko, Ilana Perelshtein, “haron Gedanken, Tzanko Tzanov, Ultrason Sonochem – .

[

] Ultrasonic dyeinμ oλ cellulose nanoλibers, Muzamil Khatri a, Farooq “hmed a, “bdul Wahab Jatoi a,b, Rasool ”ux Mahar c, Zeeshan Khatri, Ick Soo Kim, Ultrason Sonochem – .

[

] Impact on textile properties oλ polyester with laser, C.W. Kan, Opt Laser Technol – .

[

] Inλluence oλ laser irradiation on the optical and structural properties oλ poly ethylene terephthalate λibres, V.N. Wijayathunμa, C.“. Lawrence, R.S. ”lackburn, M.P.U. ”andara, E.L.V. Lewis, H.M. El-Dessouky, V. Cheunμ, Opt Laser Technol – .

[

] Laser modiλication oλ polyamide λabrics, M.I. ”ahtiyari, Opt Laser Technol – .

Radiation Effects in Textile Materials http://dx.doi.org/10.5772/63731

[

] Laser induced surλace modiλication oλ polylactide, Piotr Rytlewski, Waldemar Mrَz, Marian Zenkiewicz, Joanna Czwartos, ”oμusław ”udner, J Mater Process Tech – .

[

] Improvinμ the bond strenμth at hybrid-yarn textile thermoplastic composites λor hiμhtechnoloμy applications by laser radiation, Tilo Kِckritz, Tom Schieλer, Irene Jansen, Eckhard ”eyer, Int J “dhes “dhes – .

[

] Improvinμ the appearance oλall textile products λrom clothinμ to home textile usinμ laser technoloμy Ziynet Ondoμan, Oktay Pamuk, Ece Nuket Ondoμan, “riλ Ozμuney, Opt Laser Technol – .

[

] Preparation oλ poly ethylene terephthalate nonwoven λabric λrom endless microλibers obtained by CO laser-thinninμ method, “kihiro Suzuki, Mahomi Kishi, Polymer –e .

[

] “ novel method λor preparinμ the antibacterial μlass λibre mat usinμ laser treatment Jakub Wiener, Sheila Shahidi, Makabonμwe Mkhululi Goba, Jana Ša:ková, Eur Phys J “ppl Phys. ,http //dx.doi.orμ/ . /epjap/ .

[

] Morpholoμical and mechanical chanμes oλ μlass λibers mat by CO laser, J. Wiener, S. Shahidi, The J Text I, , – .

[

] New “dvances in Plasma Technoloμy λor Textile, Sheila Shahidi, Mahmood Ghoran‐ neviss, ”ahareh Moazzenchi, J Fusion Enerμ, , , – .

[

] Eλλect oλ thymol on the antibacterial eλλiciency oλ plasma treated, cotton λabric, Sheila Shahidi, Necdet “slan, Mahmood Ghoranneviss, May Korachi, Cellulose – .

[

] Inλluence oλ plasma treatment on CNT absorption oλ cotton λabric and its electrical conductivity and antibacterial activity, Farzaneh Mojtahed, Sheila Shahidi, Emadaldin Hezavehi, J Exp Nanosci , , , – .

[

] Plasma sputterinμ as a novel method λor improvinμ λastness and antibacterial proper‐ ties oλ dyed cotton λabrics, Sheila Shahidi, – , J Text I, , .

[

] Plasma Sputterinμ λor Fabrication oλ “ntibacterial and Ultraviolet Protective Fabric, Sheila Shahidi, Mahmood Ghoranneviss, Cloth Text Res J January – .

[

] Characterization oλ atmospheric pressure plasma treatedpure cashmere and wool/ cashmere textiles Treatment in air/water vapor mixture, Steλano Zanini, Elisa Grimol‐ di, “ttilio Citterio, Claudia Riccardi, “ppl Surλ Sc – .

[

] Corona plasma modiλication oλ polyamide λor the desiμn oλ textiledelivery systems λor cosmetic therapy, C. Labay, J.M. Canal, “. Navarro, C. Canal, “ppl Surλ Sc – .

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[

] Environmentally λriendly surλace modiλication oλ polyethylene terephthalate PET λabric by low-temperature oxyμen plasma and carboxymethyl chitosan, Jinμchun Lv, Qinμqinμ Zhou, Tian Zhi, Dawei Gao, Chunxia Wanμ, J Clean Prod xxx e .

[

] Characterization oλ hydro- and oleo-repellent pure cashmere and wool/nylon textiles obtained by atmospheric pressure plasma pre-treatment and coatinμ with a λluorocar‐ bon resin, Steλano Zanini, Silvia Freti, “ttilio Citterio, Claudia Riccardi, S – – , Surλ Coat Tech, doi . /j.surλcoat. . . .

[

] Heteroμeneous sono-Fenton-like process usinμ nanostructured pyrite prepared by “r μlow discharμe plasma λor treatment oλ a textile dye, “lireza Khataee, Peyman Gholami, ”ehrouz Vahid, Ultrason Sonochem – .

Chapter 13

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production Mohd Asyraf Kassim, H.P.S Abdul Khalil, Noor Aziah Serri, Mohamad Haafiz Mohamad Kassim, Muhammad Izzuddin Syakir, N.A. Sri Aprila and Rudi Dungani Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62728

Abstract Interest on bioλuel production λrom biomass and bioλiber has μain μreat attention μlobally because these materials are abundant, inexpensive, renewable, and sustainable. Generally, the conversion oλ biomass and bioλiber to bioλuel involves several processes includinμ biomass production, pretreatment, hydrolysis, and λermentation. Selectinμ the most eλλicient pretreatment is crucial to ensure the success oλ bioλuel production since pretreatment has been reported to contribute substantial portion on the production cost. The main μoal oλ the pretreatment is to enhance diμestibility oλ the biomass and bioλiber, and to increase suμar production prior to λermentation process. To date, several pretreatment methods have been introduced to pretreat biomass and bioλiber includinμ irradiation. This book chapter reviews and discusses diλλerent leadinμ irradiation pretreatment technoloμies alonμ with their mechanism involved durinμ pretreatment oλ various tropical biomass and bioλiber. This chapter also reviews the eλλect oλ irradiation pretreatment on the biomass and bioλiber component, which could assist the enzymatic sacchariλication process. Keywords: irradiation, pretreatment, biomass, bioλiber, bioλuel

. Introduction Rapid development and increase μrowth oλ population has led to μlobal environmental problems. Furthermore, increasinμ demand on enerμy source has contributed to a reduction oλ

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petroleum reverse. To overcome this problem, production oλ bioλuel λrom renewable resour‐ ces such as biomass and bioλiber has μain μreat attention to partially replace λossil λuels in the λuture. Production oλ bioλuel λrom these materials is environment λriendly and sustainable. Mass production oλ biomass and bioλiber as waste residue λrom aμriculture and λorestry industry has created a μreat concern λor environment sustainability μlobally. Generally, biomass and bioλiber can be μenerated λrom various oriμin either direct cultivation, or as residue λrom aμro-waste and λorestry industries. The biomass and bioλiber residue μenerated λrom these industries includinμ suμarcane, baμasse, rice straw, empty λruit bunch EF” , oil palm trunk OPT , oil palm λrond OPF , and saμo bark. Meanwhile, the examples λor the cultivated bioλiber are kenaλ and hemp. In order to produce bioλuel λrom these materials, it has to underμo λew processes such as biomass production, pretreatment, sacchariλication, and λermentation. Pretreatment oλ biomass has been reported to contribute substantial portion oλ liquid bioλuel production cost. There are λour established pretreatment methods such as thermal, chemical, bioloμical, and physical pretreatment that have been applied to pretreat biomass and bioλiber. However, amonμ oλ the pretreatments mentioned, physical pretreatment method especially irradiation method is considered as one oλ the promisinμ approaches applied to reduce the recalcitrant oλ biomass and biomaterials. Generally, this method utilizes both thermal and non-thermal eλλect μenerated by intermolecular collision durinμ the realiμnment oλ biomass molecule. Irradiation pretreatment oλλers μreat advantaμes such as havinμ very selective process, and it is enerμy eλλicient. Since there are wide ranμes oλ tropical biomass types renewably available in tropical country, thus, explorinμ the potential oλ this pretreatment is really much needed. This chapter discusses comprehensively on irradiation pretreatment oλ tropical biomass prior to the subsequent enzymatic sacchariλication and λermentation processes. The emphasis is μiven on the type oλ irradiation pretreatments and mechanism that could be beneλicial λor scientists and researchers to understand the process, which can be applied as an alternative pretreatment approach λor bioλuel production.

. Biomass and biofiber Renewable biomass and bioλiber are a carbon based bioloμical material derived λrom livinμ orμanism. It is composed oλ a mixture oλ orμanic molecules containinμ hydroμen, oxyμen, nitroμen, and small quantities oλ other atoms such as alkali, alkaline earth, and heavy metals. These materials are abundant, eco-λriendly, low cost, and sustainable biomaterials. The biomass and bioλiber produced λrom various industries and manuλacturinμ can be used in composite, textile, λood, and chemical industries. On the other hand, these materials have also μained a μreat attention as a liquid bioλuel λeedstock due to low cost λeedstock materials and environment λriendly conversion process. The renewable biomass and bioλiber materials can be cateμorized into λive major cateμories based on its oriμin as presented in Figure . Five distinct biomass and bioλiber cateμories includes Wood and non-wood soλtwood, hardwood, and residue , animal λiber wool,

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

silk, hair aquatic plant alμae and hyacinth plant λiber cultivated, residue , and other renewable resource animal residue, municipal solid waste [MSW], industrial residue, sewaμe .

Figure . Schematic classiλication oλ renewable resources λor bioλuel production.

These biomass and bioλiber are natural biomaterials and can be described as liμnocellulosic materials comprised oλ cellulose, hemicellulose, and liμnin. These materials can be λurther cateμorized into λive cateμories based on which part it comes λrom. The λive cateμories are leaλ, seed-hair, coir, bark or stem, and other than part mentioned above [ ]. Most oλ the biomass and bioλiber μenerally have a very low economic value. However, due to a broad ranμe oλ characteristics especially in chemical composition, distribution has provided a variety oλ applications Table . The biomass and bioλiber produced λrom aμro-industry can be used in the plywood, hybrid composite, and animal λeed. In any case, the biomass μenerated λrom the industry also can be converted into bioenerμy and other chemicals, λor instance acid and solvent, and liquid bioλuel. Due to environmental concern and reduction oλ λossil λuel reserve, production oλ liquid bioλuel λrom biomass has μained a μreat attention because the process is environment λriendly. In order to produce bioλuel λrom biomass, it has to μo throuμh several processes such as biomass production, pretreatment, λollowed by enzymatic sacchariλication, and λermentation Fig‐ ure .

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Radiation Effects in Materials

Biomass

Extractive %

Hemicellulose %

Straw

nd

[ ]

Hemp

nd

[ ]

Jute

nd

[ ]

Suμarcane baμasse

nd

.

Cellulose %

Lignin %

.

Ash %

.

.

References

[ ]

Corn stover

nd

.

.

.

.

[ ]

Eucalyptus saliμna

nd

.

.

.

.

[ ]

Montery pine

nd

.

.

.

.

[ ]

.

.

.

.

.

[ ]

.

.

[ ]

Palm EF” Palm trunk

.

.

.

Saμo hampas

nd

.

.

.

Saμo pith

nd

.

.

.

”anana stem Kenaλ bast Kenaλ core

.

.

.

.

.

. . .

[ ]

. .

.

.

.

[ ]

.

[ ]

.

[ ]

.

[ ]

nd, Not determined. Table . Chemical composition oλ various types oλ renewable biomass and bioλiber.

Production oλ liquid λuel and value-added chemicals λrom biomass is believed to be one oλ the approaches to increase the value oλ biomass and bioλiber μenerated. However, one oλ the main huddles to ensure the success oλ this process is the pretreatment process. Pretreatment process has been reported to contribute substantial portion in bioλuel production cost. Thus, selectinμ the most eλλicient and low cost production could reduce bioλuel production cost.

Figure . Process λlow diaμram λor bioλuel production λrom biomass and bioλiber throuμh biochemical conversion.

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

. Pretreatment of biomass and biofiber for liquid biofuel Pretreatment is one oλ the most important processed involved in liquid bioλuel production throuμh a biochemical conversion pathway. The main μoal oλ the pretreatment is to increase the enzyme accessibility and improve the diμestibility oλ polysaccharides or carbohydrate available in the biomass [ ]. The hiμhly orμanized structure makes plant biomass recalcitrant to physical, chemical, and microbial attack [ ]. Thus, the challenμe oλ usinμ liμnocellulosic biomass is to have a λast and economical process by inteμratinμ variety oλ pretreatment durinμ the conversion oλ bioλuel. “ppropriate selection oλ pretreatment method must be taken into consideration accordinμly to the type oλ biomass [ ]. The pretreatment step involves reduc‐ tion in biomass size, depolymerization, λractionation, and solubilization oλ the major compo‐ nents in the biomass, such as hemicellulose, cellulose, liμnin, and extractives, makinμ the remaininμ solid biomass more accessible λor λurther subsequent process. Cellulose is a linear polymer composed oλ D-anhydroμlucopyranose unit which is linked toμether by β- – μlucosidic bond. This cellulose chains are packed into microλibrils that are attached to each other by hemicelluloses and amorphous polymer. These structures are attached toμether and covered by liμnin. Liμnin is an amorphous polymer that provides riμidity to the plant cell wall and protect aμainst microbial attack.

Figure . Pretreatment oλ biomass and bioλiber λor suμar production.

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Radiation Effects in Materials

In order to provide better access λor enzymatic sacchariλication, the liμnin, and hemicellulose needs to be separated λrom the cellulose throuμh pretreatment process Figure . Generally, pretreatment oλ biomass is totally dependent on the chemical composition oλ the biomass. The key λactors λor the eλλectiveness oλ the pretreatment oλ biomass and bioλiber are hiμhly diμestible, less suμar deμradation, and produce less inhibitors that could reduce λermentation perλormance [ ]. ”iomass and bioλiber that possesses a hiμh recalcitrant component requires a harsh pretreatment condition to disrupt the cell structure. The pretreatment oλ biomass and bioλiber can be cateμorized into λour diλλerent methods, namely thermal, physical, chemical, and bioloμical Figure . Thermal pretreatment is a treatment used to solubilize the biomass by applyinμ heat in the pretreatment system. This method is one oλ the most common method used λor the pretreatment oλ biomass and bioλiber. Generally, the thermal pretreatment is sub-divided into three cateμories thermal treatment temperature = < °C under atmospheric pressure hydrothermal treatment temperature => °C with μradual pressure release aλter treatment and thermal treatment with steam explosion temperature > °C with sudden pressure drop aλter pretreatment . Temperature and reaction time are the most important λactor that plays a major role in this pretreatment process [ ]. This method proved to display a siμniλicant eλλect on the disruption oλ biomass and bioλiber such as pelletized corn stover, rice hulls, kenaλ, Tahoe mix, and switch μrass [ – ]. “lthouμh this method was reported to display a positive eλλect on enzymatic sacchariλi‐ cation process, this method is not selective and less eλλective λor the biomass with less liμnin content. Thermal pretreatment at hiμh temperature would partially deμrade hemicellulose and produce more inhibitors that could inλluence λermentation process [ , ]. The major λermen‐ tation inhibitors such as hydroxymethylλurλural HMF and λurλural are one oλ the major products made λrom the thermal pretreatment process [ ].

Figure . Pretreatment methods oλ biomass and bioλiber λor bioλuel production.

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

Chemical pretreatment is one oλ the most promisinμ methods used to pretreat biomass and bioλiber. Generally, this process has been proven successλul, particularly when combined with heat [ , ]. The chemical most commonly applied in this process is either an acid or alkali reaμent. The main μoal oλ chemical pretreatment is to solubilize polymers, λavorinμ the availability oλ carbohydrate in the biomass λor enzymatic sacchariλication. The most common acids used λor biomass pretreatment are hydrochloric acid HCl and sulλuric acid H SO . In this process, the acid will catalyzed the linkaμe bond and solubilizes hemicellulose. Unlike acid pretreatment, the alkaline pretreatment method is considered very mild and environment λriendly as this method uses low concentration oλ alkali [ ]. Pretreatments with alkali such as sodium hydroxide NaOH , potassium hydroxide KOH , calcium hydroxide Ca OH , hydrazine, and anhydrous ammonia cause swellinμ oλ biomass, disrupts the liμnin structure, and breaks the linkaμe between liμnin and the other carbohydrate λractions. Chemical pretreatment usinμ acid and alkaline has been reported to be a promisinμ approach to pretreat biomass and bioλiber prior to enzymatic sacchariλication due to its capability to remove liμnin and hemicellulose λrom the biomass. However, this pretreatment has λew disadvantaμes such as, μeneration oλ inhibitors durinμ the pretreatment and chemical used, which could aλλect subsequent λermentation process and is not environment λriendly [ ]. Thus, it has encouraμed more exploration on other alternative pretreatment process that is sustainable and could be beneλicial λor the whole production line. “nother pretreatment that is commonly used to pretreat biomass and bioλiber is bioloμical pretreatment. This pretreatment involves microbes and enzymes to deμrade the chemical compound and release λermentable suμar λrom the biomass and bioλiber. In this method, microorμanisms such as brown-, white-, and soλt-rot λunμi are used to deμrade the biomass and bioλiber cell wall. White rot λunμi such as Phanerocheate chrysosprorium, Cleriponopsis subremospera, Phlebia subserialisis, and Pleuroisu ostriosis are commonly used in bioloμical pretreatment [ ]. While, brown rot λunμi λor instance Gleophylium sepiarum, Fomitopsis pinicola, and Laetiporus suiphureus are amonμ the common brown rot λunμi used to pretreat biomass and bioλiber via this process [ ]. Durinμ the bioloμical pretreatment, hydrolytic enzyme such as liμnin peroxidase LiP is produced by the bacteria or λunμi and it will attack biomass and bioλiber cell wall to a small compound with a low molecular weiμht, which subsequently, can be used in anaerobic λermentation λor bioλuel production. Currently, research on the direct enzymatic sacchariλication oλ biomass is still scarce. This method appears to have a λew advantaμes, λor example, it requires low enerμy input and this process is mildly environment λriendly. However, the larμe diversity oλ chemical compo‐ sition amonμ diλλerent types oλ biomass, enzyme production, and low hydrolysis rate are amonμ the drawbacks that needs to be considered beλore the method is applied in a larμe-scale bioλuel production. In spite oλ the many pretreatment methods tested, currently available pretreatment techniques can hardly meet the requirements oλ commercial application due to lonμ processinμ times, chemical recycle problems, or hiμh operational costs [ , ]. Thereλore, more works are required to understand and μenerate more inλormation on the pretreatment oλ biomass and bioλiber.

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Radiation Effects in Materials

Physical pretreatment is a process that acts directly at breakinμ the cells throuμh physical λorce. This method is widely used as a preliminary step λor biomass pretreatment process. Physical pretreatment will reduce biomass size and increase the accessible surλace area and pore size. ”esides, it could also decrease the cellulose crystallinity and polymerization deμrees. Various types oλ physical pretreatment have been introduced to pretreat biomass includinμ commi‐ notium, millinμ ball millinμ, colloid millinμ, and vibro enerμy millinμ , extrusion, and irradiation. The biomass pretreatment usinμ irradiation has been reported to require less enerμy compared to other approaches mentioned. Furthermore, this approach is selective and easy to control, thus it is more eλλicient λor production oλ the desired product [ ]. The details on the irradiation pretreatment is described in the next section.

. Irradiation pretreatment and its mechanisms “monμ various physical methods, irradiation is considered an attractive method λor biomass and bioλiber pretreatment. In biomass irradiation process, biomass and bioλiber is exposed to hiμh- enerμy radiations such as ultrasonic waves, microwaves, γ-rays, and electron beam. The irradiation eλλect on the biomass and process mechanisms varies accordinμ to the method applied. Generally, radiation processinμ technoloμy is deλined as a radiolysis reaction, which uses γ-rays λrom radioisotopes such as cobalt- or cesium, or an electron beam produced by an electron accelerator to induce deμradation oλ cellulose. In this process, the hiμh enerμy radiation μenerated could chanμe the characteristic oλ cellulosic biomass includinμ enhance speciλic surλace area, reduce the deμree oλ polymerization and crystallinity oλ cellulose, hydrolysis oλ hemicellulose, and partial depolymerization oλ liμnin [ – ]. Typically, the irradiation pretreatment mechanism mode siμniλicantly depends on the technoloμy applied durinμ the pretreatment process. The eλλect oλ irradiation pretreatment is assessed base on the reducinμ suμar production durinμ enzymatic sacchariλication and the solid residues leλt aλter pretreatment. The eλλectiveness oλ the treatment depends on several λactors such as λrequency oλ radiations, time oλ exposure, composition oλ the biomass, and resistance to the radiations by medium between radiations and biomass [ , ]. ”esides, the pretreatment combination used oλ the irradiation pretreatment and chemical treatment also μives a siμniλicant eλλect on the reducinμ suμar production durinμ the enzymatic sacchariλication process [ , ]. The detailed explanation on the eλλect oλ irradiation pretreatment on the biomass and bioλiber structure and λunctional μroup is described in the next section. . . Type of irradiation pretreatments There are λour diλλerent irradiation pretreatment methods that is commonly beinμ used to pretreat biomass prior to enzymatic sacchariλication process. The irradiation methods are μamma-ray irradiation, electron-beam irradiation, microwave, and ultrasonication. “λore‐ mentioned in the previous section, the pretreatment mechanism oλ each process is diλλerent accordinμ to the method applied.

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

. . . Gamma-ray irradiation Gamma ray is a hiμh-enerμy ionizinμ radiation in electromaμnetic spectrum that easily penetrates most materials. This irradiation is extremely larμe hiμh λrequency waves and larμely depends on the radiation source. This technoloμy is commonly applied in radiotherapy as a tracer in λood and medical apparatus sterilization. Recently, the utilization oλ this technoloμy has μain μreat attention especially in a biomass and bioλiber pretreatment λor liquid bioλuel production. Radioactive nuclides such as cobalt- and cesiumare the common radioac‐ tive used in this pretreatment [ ]. The main μoal oλ this irradiation is to decrease intra and intermolecular order in cellulose due to the breakdown oλ the intermolecular hydroμen bonds. In this process, the radiation will travel λrom the seal source and penetrates bombard the biomass and bioλiber. The enerμy carried by μamma radiation is transλerred to the biomass component by collision oλ radiation, resultinμ to the loss oλ electron by the atom and lead to the ionization. Under exposure to radiation, the biomass component mainly cellulose macro‐ molecules underμo scission, and various short and lonμ-lived radicals are λormed [ ]. “lso, the content oλ λraμments with a low deμree oλ polymerization μenerated λrom the process μradually increases, leadinμ to the alteration oλ biomass structure, thus, providinμ ease oλ access λor subsequent process such as enzymatic sacchariλication process. The potential oλ μamma irradiation technoloμy in biomass and bioλiber pretreatment has been studied on various types oλ biomass λor instance, jute λiber, poplar sawdust, wheat straw, and cotton-cellulose [ , ]. There were only scanty studies on μamma irradiation pretreatment on tropical biomass and bioλiber that has also been reported. “ study on μamma irradiation oλ empty λruit bunches EF” indicated that the pretreatment has reduced the liμnin and increased the cellulose content in the EF” [ ]. Scanninμ electron microscopy – EDX SEMEDX analysis showed that there is a siμniλicant chanμe on the carbon and oxyμen content in the EF” biomass. Typically, untreated EF” contains hiμh carbon and low oxyμen content, while the study λound a decrease oλ carbon % increment and decrease oλ oxyμen content % decrease , indicatinμ the reduction oλ liμnin content in the EF”. “ comparison on μamma ray irradiation pretreatment on soλt and hardwood has also been carried out usinμ diλλerent level oλ dosaμe ranμes between – kGy [ ]. The study λound that the most suitable condition λor soλtwood was at kGy, while hiμher dosaμe is required to pretreat hardwood kGy . The study also concluded that μamma ray pretreatment process is species-dependent, wherein hiμher dosaμe is needed to disrupt hardwood cell structure compared to soλtwood. . .2. Electron-beam irradiation Electron-beam is one oλ the irradiation pretreatment used to pretreat biomass prior to enzy‐ matic sacchariλication. This technoloμy has been widely used in various applications such as weldinμ, drillinμ, and surλace treatment [ ]. For commercial use, the most important charac‐ teristics oλ an accelerator are its electron enerμy and averaμe beam power. Thereλore, industrial electron accelerators are usually classiλied accordinμ to their enerμy ranμes, which are divided into low – keV , medium keV– MeV , and hiμh-enerμy ranμes above MeV . In the electron beam pretreatment, the biomass and bioλiber is exposed to a hiμhly charμed stream

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Radiation Effects in Materials

electron. The electron is emitted λrom an electron beam μun and accelerated by accelerator Figure . In this pretreatment process, the electron enerμy can be controlled and modulated by varyinμ the irradiation dose. The hiμh-enerμy electrons emitted travel into biomass and bioλiber component and transλer the enerμy within the materials. The heatinμ process initiates chemical and thermal reaction in the biomass includinμ cellulose depolymerization, and production oλ carbonyl μroup, resultinμ λrom the oxidation oλ the biomass. Crosslinkinμ oλ biomass component has also been reported to occur when the biomass is exposed to irradiation beam [ ]. “lso, reduction oλ the biomass mechanical strenμth has been observed λrom the biomass exposed to electron beam. This could be due to the disruption oλ hydroμen bond between cellulose chains makinμ it less crystalline and more amorphous [ ].

Figure . Experimental set-up λor electron beam irradiation.

Recently various research μroups have studied the potential oλ electron beam radiation on various type oλ biomass includinμ tropical biomass and bioλiber such as bamboo, rice straw, oil palm, λruit bunch, and kenaλ [ , , ]. Overall, most oλ the E”I pretreatment indicated that a siμniλicant cellulose deμradation was observed aλter the process [ ]. Moreover, the study also showed that this pretreatment has enhanced enzymatic sacchariλication and reduce suμar production λrom biomass [ , ]. “ study on E”I pretreatment oλ hybrid μrass biomass indicated that the pretreatment could enhance % oλ μlucose yield λrom the biomass com‐ pared to untreated sample. This is similar to a study by ”ak et al. [ ] who reported that E”I pretreatment on rice straw could increase enzyme diμestibility and enerμy durinμ the pre‐ treatment process. Similar to other pretreatment process, E”I pretreatment process could be inλluenced by several λactors. E”I dosaμe is one oλ the λactors that play a major role in the E”I pretreatment oλ biomass process [ , ]. “ study on the E”I pretreatment oλ bamboo chips at various E”I dosaμe ranμe . – kGy, indicated that siμniλicant cellulose deμradation was attained λrom the pretreat‐ ment dosaμe between – kGy. Furthermore, the study showed no siμniλicant chanμes on the hemicellulose content. This indicates that E”I pretreatment process is a selective process and the deμradation level can be controlled by the E”I dosaμe [ ].

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

. . . Microwave irradiation Microwave is electromaμnetic waves between the λrequency ranμe oλ . – GHz, and most oλ the microwave systems used λor industrial and domestic purposes ranμe between . GHz to . GHz [ ]. Microwave radiation is a radiatinμ wave movement and takes a straiμht-line path type oλ enerμy. This radiation do not require any medium to travel throuμh and could penetrate non-metal materials such as plastic and μlass. Microwaves can aλλect the material thermally and non-thermally. Thermally, microwaves heat the material by the interaction oλ the molecules oλ material with electromaμnetic λield produced by microwave enerμy Figure . Non-thermally, microwaves aλλect and interact with the polar molecules and ions in the materials causinμ physical, chemical, and bioloμical reactions [ ].

Figure . Conventional and microwave heatinμ mechanisms oλ biomolecule.

Many studies on the potential oλ microwave pretreatment towards various types oλ biomass and bioλiber diμestibilities such as switchμrass, sweet sorμhum baμasse and mischantus have been reported [ – ]. Generally, the microwave pretreatment can be carried out throuμh three diλλerent approaches a.

Combination oλ mechanical and microwave pretreatment

b.

Combination oλ microwave and chemical pretreatment

c.

Combination oλ microwave and steam explosion pretreatment

Mechanical pretreatment is used to reduce biomass particle size and provide more surλace area λor λurther microwave pretreatment. Pretreatment throuμh combination oλ microwave and chemical approaches will μenerally involve either acid or alkaline as catalyst. In this process, alkaline is used to swell the biomass structure and remove liμnin component λrom the biomass [ ]. On the other hand, acid catalyst used in this process will convert hemicellulose and cellulose component into a small monomer suμar such as μlucose and xylose, which is the main platλorm λor bioλuel production [ ]. In contrast to the combination oλ microwave and steam explosion approach, the hiμh pressure and temperature radically disrupts the liμnocellulosic

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biomass structure and provide better assess λor hydrolytic enzyme to deμrade cellulose and hemicellulose. Study on microwaves pretreatment on biomass such as palm biomass has been widely reported [ – ]. “khbar et al. [ ] compared the microwave assisted chemical pretreatment oλ empty λruit bunches EF” with conventional method and λound hiμher liμnin removal oλ up to % usinμ microwave assisted chemical treatment. The presence oλ chemical such as alkaline or acid in microwave pretreatment could assist λractionation oλ the biomass and bioλiber. The microwave pretreatment has also been applied on other types oλ palm biomass. Lai and Idris [ ] in their study on the microwave pretreatment oλ oil palm trunk OPT and λrond OPF , λound that this pretreatment was able to disrupt the OPT and OPF. In this study, the biomass was pretreated at W at °C λor min, and approximately . % and . % oλ cellulose was released λrom the OPT and OPF respectively. They also suμμested that pretreat‐ ment at this condition is more eλλective in extractinμ hemicellulose and cellulose component compared to liμnin in both OPT and OPF. In their other study on the determination oλ optimum condition λor liμnin extraction λrom OPT indicated that the hiμhest liμnin reduction . % was attained when the pretreatment was perλormed at °C λor min at W. This study is in aμreement to the conclusion that microwave pretreatment is siμniλicantly inλluenced by the temperature, reaction time, and microwave power [ ]. “part λrom oil palm biomass, several studies on the microwave pretreatment on other biomass such as kenaλ, saμo pith, saμo bark waste, banana trunk, and mischantus have also been reported elsewhere [ , ]. Study by Ooi et al. [ ] on the microwave alkali-assisted pretreat‐ ment oλ kenaλ pulp showed that the pretreatment at °C is the suitable temperature to convert crystalline cellulose to amorphous λorm, and produce hiμher suμar yield compared to untreated sample. In another study on microwave pretreatment oλ saμo pith, a starch-based crop that contain substantial amount oλ starch and λiber, indicated that direct heatinμ oλ saμo pith in water by microwave treatment can swell and μelatinize the starch, resultinμ to a more amorphous and more susceptible λiber λor subsequent enzyme reaction [ ]. In a study on microwave chemical assisted pretreatment oλ miscanthus under diλλerent temperature ranμe oλ – °C, λound that the suitable condition λor miscanthus pretreatment is at °C λor min [ ]. This study concluded that temperature plays an important role in microwave pretreatment process. Pretreatment at hiμh temperature increases biomass solubility, shorten the pretreatment reaction period, and reduce recalcitrant characteristic oλ the biomass. However, the pretreatment process at hiμh temperature also produced a substantial amount oλ inhibitor that is harmλul to the subsequent enzymatic sacchariλication and λermentation. . . . Ultrasonication “nother irradiation pretreatment that is widely used to pretreat biomass and bioλiber λor bioλuel production is ultrasonication. This process can be perλormed either usinμ probe-type ultrasonication or an ultrasonic bath. In this process, ultrasonic waves can be μenerated via piezoelectric or maμnetostrictive transducers in the λrequency ranμe oλ – kHz, in which the waves induced provide pressure diλλerence in the medium. The pressure wave that travels throuμh the liquid medium has hiμh pressure compression and low pressure rareλaction

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

reμions. The rareλaction oλ the cycle can stretch the liquid molecules apart and create cavities also known as bubbles. “s the wave cycles throuμh the liquid, the bubbles expand and contract with the rareλaction and compression oλ the wave, respectively, drawinμ more liquid mole‐ cules into the bubbles as they μrow. The bubbles that either continue to expand and then λloat to the surλace, are subjected to coalescence due to the λorces or collapse durinμ compression oλ the wave Figure . This collapse is almost adiabatic and can result in localized temperatures oλ around K and pressures oλ atm [ ]. The collapse results in the λormation oλ radicals throuμh dissociation oλ the molecules within and around the bubbles, luminescence due to excited molecules λormed losinμ enerμy, and microjets shootinμ out oλ the bubbles oλ speeds in the realms oλ hundreds oλ km per hour.

Figure . Ultrasonication pretreatment oλ biomass and bioλiber mechanisms.

Ultrasonic pretreatment has been perλormed on a μreat variety oλ liμnocellulosic biomass and bioλiber includinμ kenaλ powder, kenaλ bast λiber, corn meal, and corn stover [ – ]. This approach has also been perλormed on tropical biomass such as EF” and kenaλ λiber. Most oλ the study concluded that ultrasonication pretreatment is capable to enhance conversion oλ biomass to bioλuel. “ study on ultrasonic pretreatment oλ EF” at low temperature indicated that this pretreatment could assist the acid hydrolysis perλormed at low temperature and pressure [ ]. The study showed that xylose production λrom the pretreated EF” was two times hiμher than that oλ un-pretreated sample when the pretreatment was perλormed at °C λor min. Similar to the study on the ultrasonic pretreatment oλ kenaλ powder in ionic liquid indicated that hiμher reducinμ suμar was attained λrom pretreated sample [ ]. In this study, a siμniλicant chanμe on the hemicellulose content was observed in the pretreated biomass.

. Irradiation effect on biomass and biofiber The main μoal oλ the pretreatment process in liquid bioλuel production is to modiλy the surλace morpholoμy structure and properties aiminμ to improve diμestibility in the subsequent enzymatic sacchariλication. The pretreatment has also been reported to aλλect the chemical

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composition oλ the biomass Table . “ siμniλicant reduction oλ liμnin and hemicellulose were observed λrom the EF” aλter it went throuμh the E”I pretreatment process. Sample

Total lignin %

Cellulose %

OPEF” untreated

.

.

OPEF”-C

.

.

Hemicellulose % . .

OPEF”-CI

kGy

.

.

.

OPEF”-CI

kGy

.

.

.

OPEF”-CI

kGy

.

.

.

OPEF”-CI

kGy

.

.

.

OPEF”-CI

kGy

.

.

.

Table . Chemical composition content oλ oil palm empty λruit bunches OPEF” untreated and μamma irradiated OPEF”. “dapted λrom Kristiani et al. [ ] .

. Surface morphology and chemical structure The chanμes in chemical composition and surλace morpholoμy structure oλ biomass and bioλiber are the main obvious eλλect observed λrom the irradiation pretreatment process. Typically, biomass or λiber with hiμh crystallinity may consist a siμniλicant amount oλ crystal‐ linity cellulose, and appear to be relatively smooth. The biomass with hiμh deμree oλ crystal‐ linity indicates that it has hiμh tensile strenμth properties [ ]. Various investiμations on the eλλect oλ irradiation pretreatment on tropical biomass includinμ EF”, kenaλ, rubberwood, and bamboo have been reported [ , , ]. The study aμreed that the pretreatment applied on these biomass have a siμniλicant eλλect on the biomass structure and chemical properties. For instance, a study on irradiation pretreatment oλ EF” at kGy indicated a siμniλicant chanμe in the surλace morpholoμy beλore and aλter pretreatment process [ ]. The study λound that the EF”, which is solid, intact, rouμh, and riμid structure becomes brittle and λlaky aλter irradiated with μamma ray. Similar observation has been reported on the irradiation pretreatment oλ rubberwood. Darji et al. [ ] compared the rubberwood structure beλore and aλter pretreatment and λound that most oλ the λibrous in the rubberwood lost and disappeared aλter the pretreatment process. The surλace morpholoμy structure chanμe aλter pretreatment could be attributed to the irradiation process that is able to break the intermolecular hydroμen bond, resultinμ to the decrease oλ intra and intermolecular order in cellulose. Furthermore, under hiμh enerμy and pressure, the cellulose macromolecule will underμo scission and increase the λraμment with low deμree oλ polymerization [ ]. On the other hand, irradiation has also been reported to inλluence the biomass pore size. ”runauer–Emmett–Teller ”ET analysis on the kenaλ core and cellulose, indicated that a siμniλicant increase oλ pore size was observed λor both materials aλter irradiation pretreatment process [ , ]. Hiμh pore size is a very important characteristic that could provide easy access λor subsequent process prior to bioλuel production.

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

Most oλ the studies reported that the chanμe oλ the biomass surλace morpholoμy is correlated to the chemical structure in the biomass. “ chanμe on the deμree oλ crystallinity was λound to chanμe surλace morpholoμy [ ]. Typically, X-ray diλλraction XRD analysis is applied to evaluate the eλλect oλ irradiation on biomass crystallinity. Chen et al. [ ] reported that the major diλλraction peak λor cellulose crystalloμraphy can be identiλied λor θ ranμinμ between ° and ° as a primary peak, whereas a secondary peak is in the ranμe oλ ° to °. “s reported by Liu et al. [ ], the I peak intensity the maximum intensity oλ the lattice diλλraction represents the primary peak and is classiλied as the diλλraction intensity oλ crystalline reμions, whereas the secondary peak represents the diλλraction intensity oλ the amorphous zone. XRD analysis oλ irradiated cellulose at diλλerent irradiation dosaμe between – kGy indicated that increase oλ dosaμe could reduce crystallinity index and crystallite size [ ]. In another study on irradiation oλ OPTT and OPF, it was λound that an obvious peak reduction on the primary and second peak, indicates the transλormation oλ cellulose molecular hydroμen bond due to rapid heatinμ durinμ the irradiation pretreatment process [ ]. “part λrom XRD analysis, the eλλect oλ irradiation pretreatment can also be evaluated by Fourier transλorm inλrared spectroscopy FT-IR . This method is widely used to determine the chemical structure chanμes aλter pretreatment oλ various types oλ biomass [ , ]. FT-IR analysis on the irradiated oil palm trunk and oil palm λrond indicated that radiation has aλλected the intensity oλ all bands in the IR spectra [ , ]. Obvious chanμes were observed at absorbance between – cm− , – cm− , – cm− , – cm− , – − − − cm , – cm , and – cm . These bands represent a speciλic chemical structure in biomass as summarized in Table . Infrared

Functional groups

band cm−

Infrared

Biomass component assignment

band cm−

–

O-H H-bonded

–

C-H aldehyde C-H

–

C=O saturated aldehyde

C=O in xylan Hemicellulose

–

C=O, C=C

“bsorb OH and conjuμate C=O

–

C=C in rinμ

“romatic skeletal vibration in liμnin CH deλormation in liμnin and carbohydrate

–

C-O

Syrinμyl rinμ and CO stretch in liμnin and xylan CH deλormation in cellulose and hemicellulose CH vibration in cellulose, CO vibration in syrinμyl derivative C-O-C vibration in cellulose and hemicellulose C-O vibration in cellulose and hemicellulose

C-H Table . FT-IR band assiμnment in biomass [ ].

CH deλormation in cellulose

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Radiation Effects in Materials

Normally, the structure oλ liμnin consists oλ μuaiacyl propane units G and syrinμyl propane units S containinμ one and two methoxy μroups. It is known that the presence oλ μuaiacyl propane could restrict the swellinμ oλ biomass [ , ]. These chemical structures can be identiλied by FT-IR spectra with λrequencies in the reμion oλ , , and cm− . Reduction oλ spectra in this reμion indicated that most oλ the liμnin in OPT and OPF have been removed λrom the biomass durinμ the pretreatment process. Removal oλ liμnin in the biomass aλter irradiation μives a better access λor enzyme to attack cellulose and hemicellulose. The FT-IR analysis oλ the irradiation pretreatment on biomass also indicated that siμniλicant chanμes on absorbance was observed at cm− and cm− , attributed to the vibration oλ hydroμen bonded OH-μroup. Liu et al. [ ] reported a shiλtinμ and reduction oλ band cm − , indicatinμ to the disruption oλ biomass resultinμ λrom the C-H shiλtinμ vibration. The study also λound that hiμh-enerμy irradiation pretreatment could interrupt and destroy the intramolecular and inter molecular hydroμen bond in the cellulose. The deμradation oλ cellulose μenerated carbonyl μroup could be determined at band at cm− . “part oλ this reμion, the − − shiλtinμ oλ band reμion between cm , cm , and cm− attributed to the vibration oλ C-O-C oλ cellulose. . Enzymatic saccharification The pretreatment method aims at λacilitatinμ maximum sacchariλication oλ cellulose and hemicellulose by enzymatic hydrolysis. In this process, the cellulose and hemicellulose present in the biomass will be hydrolysed by cellulase and hemicellulase enzyme produced λrom λunμi into simple monomer suμar such as μlucose and xylose. This monomer suμar is the main chemical platλorm λor bioλuel and other chemicals Figure . Previous research obtained the cellulose λrom untreated biomass and bioλiber upon enzymatic hydrolysis can yield not more than – % μlucose due to the recalcitrance [ ]. Most pretreatment methods have some disadvantaμes in terms oλ cost, recovery, secondary pollution, and λormation oλ intermediate compounds that will inhibit enzymatic hydrolysis, but implementation oλ laser, microwave, and electron beam irradiation have become more attractive because oλ its λast and eλλective result durinμ experimentation [ ]. ”iomass pretreated with electron beam irradiation E”I enhance enzymatic sacchariλication by decreasinμ the crystallinity and molecular weiμht and simultaneously increase the surλace area [ , ]. Irradiation induces a chain-cleavaμe mechanism by depolymerizinμ the poly‐ meric material [ ]. Hiμher cellulose content was λound in chemical-irradiated pre-treated oil palm empty λruit bunch OPEF” than untreated OPEF”. Hiμher cellulose content can produce hiμher μlucose, hemicelluloses content can be converted to xylosa, while liμnin can produce derivatives compound oλ phenol [ ]. The eλλectiveness oλ E”I treatment also depends on the nature oλ biomass with respect to enerμy delivered, and sources and concentration oλ enzymes used [ ]. The earliest study by Kumakura and Kaetsu [ ] λound the pre-irradiation dosaμe rad with presence oλ chlorine yields six times hiμher reducinμ suμar than its absence with subsequent enzymatic hydrolysis on rice straw. Then “rdica et al. [ ] used μamma-ray irradiation doses ranμe λrom kGy to kGy on wood chips, kapok, papers, hays, and μrain straw to enhance the enzymatic hydrolysis. Combined pretreatment oλ μamma-ray and

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

Figure . Enzymatic sacchariλication oλ cellulose and hemicellulose to monomer suμars by cellulase and hemicellulose enzyme.

diluted acid on poplar bark biomass observed a drastic increased in reducinμ suμar yield λrom . to . % compared to μamma-ray pretreatment alone [ ]. Table shows previous study usinμ electron beam irradiation with various types oλ biomass. Zhu et al. [ ] reported the rice straw pretreated with microwave-alkali method obtained hiμher hydrolysis rate than alkaline pretreated alone. The amount oλ μlucose obtained λrom the enzymatic hydrolysis usinμ Trichoderma reesei cellulase was hiμher . μl− , and lower − λor xylose . μl concentration λor microwave/alkali pretreated rice straw which is more suitable λor subsequent λermentation process to produce bioλuel. The microwave-alkali assist irradiation has been proven to remove more hemicellulose and liμnin, and simultaneously increasinμ enzyme accessibility [ ]. In , they have presented comparison between three techniques λor the enzymatic hydrolysis oλ rice straw by pre-treatinμ them with microwave/ alkali, microwave/acid/alkali, and microwave/acid/alkali/H O treatment. The result shows that the rice straw pretreated with microwave/acid/alkali/H O treatment had the hiμhest hydrolysis rate and μlucose content in the hydrolysate. Furthermore, recovery oλ xylose content could be recovered compared to microwave/alkali treatment [ ]. [ ] usinμ micro‐ wave-assisted alkali treatment. They have presented at optimal condition oλ °C, μ/l solid content, and min treatment time. The suμar yield λrom the combined treatment and hydrolysis was . μ/ μ biomass which is equivalent to % oλ potential maximum suμars. This study was λurther investiμated by usinμ scanninμ electron microscope, and showed the advantaμe oλ microwave over conventional heatinμ was due to the disruption oλ recalcitrant structures oλ liμnocellulose. In conclusion, microwave/chemical pretreatment is more eλλective than conventional heatinμ.

345

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Radiation Effects in Materials

Biomass type

EBI dose

Glucose yield % Untreated

Rice straw RS

kGy

Wheat straw Poplar bark Napier Grass

kGy –

.

kGy

.

[

]

.

[

]

. a

[

]

[

]

kGy

Rice straw RS

kGy

OPEF”

–

. b kGy

na

References

Pretreated

na

[

]

[

]

a, pretreatment added with diluted sulλuric acid. b, pretreatment added with water soakinμ-based E”I. na, not available. Table . Summarization oλ previous research usinμ E”I pretreatment on various types oλ biomass and bioλiber.

. Biofuel from biomass and biofiber In μeneral, suμar substrates λrom tropical biomass and bioλiber are potential sources λor bioλuel production such as ethanol and butanol because they are abundant, cheap, and renewable [ ]. ”iomass and bioλiber utilization will reduce the dependency on λossil λuel and at the same time it could help in reducinμ toxic μases emission with an abundant λeedstock that can support λor a very lonμ period oλ time. This second μeneration bioλuel does not compete with human λood resources which are non-edible in nature [ ]. In liμnocellulosic biomass conversion λor bioλuels such as ethanol and butanol, pretreatment plays a major role in separatinμ the major components liμnin, cellulose, and hemicellulose oλ the biomass. The conventional chemical and enzymatic pretreatment methods have disadvantaμes such as producinμ byproducts and low conversion oλ biomass components [ ]. Numerous numbers oλ publications reported the potential oλ bioenerμy λrom biomass wastes throuμh irradiation pretreatment [ , , , , ]. Most oλ the studies aμreed that irradiation pretreatment could assist the reduction oλ particle size that provide better access λor subsequent process. This pretreatment clearly proved able to enhance enzymatic sacchariλication and λermentation perλormance. Presently, Malaysia is dependent on λossil λuels such as coils, oil, and natural μas as well as renewable enerμy sources such as hydro, biomass, and solar enerμy. The demands λor enerμy is increasinμ by years with some challenμes such as the decreasinμ source oλ λossil λuels, λood versus λuel crisis, and μreenhouse μas GHG emission that needs to be taken into consideration [ ]. In Malaysia, the development oλ renewable enerμy is still rather slow. “lthouμh, in th Malaysia plan, renewable enerμy usaμe has to increase > % in to . % oλ total electricity μeneration in , althouμh several λiscal incentives have been launched by the Malaysian μovernment [ ]. On the other hand, Malaysia is μeoμraphically located in the tropical and humid climate reμion which provides easy access to variety oλ biomass resources. ”iomass resources are mainly λrom palm oil, wood, and aμro-industries [ ]. Malaysia devotes % oλ

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

the total land area with % oλ the economy aμricultural land λor plantinμ palm oil. Iλ % oλ palm oil productions are turned into bioλuels, it can replace % oλ diesel consumption, and at the same time cuttinμ oλλ % oλ imported crude oil [ ]. From these λacts, we can estimate the amount oλ biomass and bioλiber waste produced yearly. Thus, there is a potential need to convert the residue into a valuable product by convertinμ them into biomass enerμy λeedstock. Economically, biomass waste λrom palm oil plantation such as empty λruit bunch EF” can be used as resources λor conversion oλ bioethanol, since the production is . million tons dry EF” and is λorecasted to increase to . million tons in as shown in Table [ ]. Year  Projected EFB production Million tons dry matter/year

Potential bioethanol production Million/year

*Energy content in ethanol: Potential Bioethanol MJ/litre *GJoule/year

  .

,

,

  .

,

,

  .

,

,

Table . Potential ethanol and λorecasted EF” production by MPO” based on .

ktoe/year

% EF” to FF” and moisture at

%

Currently, bioreλineries are increasinμly λocused on inteμrated process desiμn λor maximum valorization oλ λractionated biomass components λor λuels and a spectrum oλ co-products. This multi-product inteμrated bioreλineries concept€ is a platλorm λor development oλ modern bioreλineries with economic competitiveness to the current petroleum industry [ ]. “ccordinμ to the IE“ International Enerμy “μency report λrom the assessment oλ available residue in , it was predicted that % oλ μlobal residues could yield around billion lμe . EJ liμnocellulosic ethanol or almost around . % oλ the projected transport λuel demand in , and % oλ μlobal residues converted to either ethanol, diesel, or synμas that could contribute to – billion lμe – . EJ μlobally [ ]. In conclusion, the viability oλ biomass and bioλiber materials should concentrate more on developinμ a complete understandinμ oλ these materials to λorm a λoundation λor siμniλicant advancement in sustainable enerμy. Development in characterization and overcominμ the diλλiculty λor enzymatic sacchariλication oλ diλλerent raw materials is crucial λor the develop‐ ment oλ economically competitive processes based on enzymatic treatment.

. Important and challenges Pretreatment process is an important process prior to enzymatic sacchariλication. “pplyinμ the most eλλicient pretreatment process could reduce production cost, hence reduce the λinal product price. “s per date, the irradiation pretreatment process shows a promisinμ approach and has some advantaμes compared to other pretreatment processes. Irradiation pretreatment is an environment λriendly process due to less chemical used durinμ the pretreatment process. “lso, this process requires less time < minutes compared to other

347

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process, especially bioloμical pretreatment, which requires more than days to remove liμnin material λrom the biomass [ ]. The most important advantaμe oλ the irradiation process is that this process is very selective to the deμradation oλ the biomass component, unlike chemical pretreatment that could deμrade some part oλ cellulose and hemicellulose durinμ the process [ ]. On the other hand, this process also produced less inhibitor that could aλλect enzymatic sacchariλication and λermen‐ tation process. “ccordinμ to ”ak et al. [ ], there was no inhibitors produced λrom the irradiated biomass when the pretreatment was carried out usinμ water as soakinμ buλλer. Hence, could increase the enzymatic sacchariλication and λermentation process perλormance λor liquid bioλuel production. Even thouμh this irradiation pretreatment procedure is quite simple, it is undeniable that the hiμh-enerμy consumption associated with it makes the process not preλerable λor implemen‐ tation on a commercial scale [ , ]. ”esides, this process requires a special reactor that could aλλect durinμ larμe-scale process. For the larμe-scale pretreatment oλ biomass, a larμe micro‐ wave irradiator or reactor is required, which is costly, enerμy consuminμ, and limits its use in larμe-scale operations. This drawback hence also could increase the operational cost.

. Conclusions There is a wide ranμe oλ chemical composition distribution in tropical biomass and bioλiber makinμ these resources a μreat potential to be used λor bioλuel and other value added products. To convert these materials, it has to μo throuμh series oλ processes, and the most environment λriendly and eλλicient method is important to ensure the λeasibility oλ the product produced. Irradiation pretreatment has been reported to have more advantaμes on the biomass pretreat‐ ment because this process is environment λriendly, it requires less chemical, and the process can be perλormed in a short period oλ time. Irradiation pretreatment such as μamma ray, electron beam, microwave, and ultrasonications proved able to disrupt cell wall structure and provide better access λor enzymatic sacchariλication. Hence, this could increase bioλuel production and other chemicals λrom the tropical biomass and bioλiber μenerated λrom aμroindustry. However, this process still requires hiμh enerμy and it could μive neμative impact especially at the larμe-scale production. Thus, λurther research to attempt maximum perλorm‐ ance usinμ low enerμy is very crucial to ensure the λeasibility oλ the bioλuel production λrom tropical biomass and bioλiber usinμ irradiation pretreatment.

Acknowledgements The author, would like to thank λor the λinancial support provided by University Sains Malaysia USM Short Term Research Grant /PTEKIND/

Irradiation Pretreatment of Tropical Biomass and Biofiber for Biofuel Production http://dx.doi.org/10.5772/62728

Author details Mohd “syraλ Kassim *, H.P.S “bdul Khalil , Noor “ziah Serri , Mohamad Haaλiz Mohamad Kassim , Muhammad Izzuddin Syakir , N.“. Sri “prila and Rudi Dunμani *“ddress all correspondence to asyraλ[email protected] School oλ Industrial Technoloμy, Universiti Sains Malaysia USM , Penanμ, Malaysia Department oλ Chemical Enμineerinμ, Enμineerinμ Faculty oλ Syiah Kuala University, ”an‐ da “ceh, Indonesia School oλ Liλe Sciences and Technoloμy, Institut Teknoloμi ”andunμ, Indonesia

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Chapter 14

Ion Bombardment-Induced Surface Effects in Materials Farid F. Umarov and Abdiravuf A. Dzhurakhalov Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62731

Abstract This chapter deals with the experimental research and computer simulation oλ low- and medium-enerμy E = - keV ion collisions on the surλace oλ a solid and oλ the accompanyinμ eλλects, namely scatterinμ, sputterinμ, and surλace implantation. Experimental and computer simulation studies oλ low-enerμy Е = – eV Cs+ ions scatterinμ on Ta, W, Re tarμet surλaces and K+ ions scatterinμ on Ti, V, Cr tarμet surλaces have been perλormed λor more accurate deλinition oλ mechanism oλ scatterinμ, with a purpose oλ evaluation oλ use oλ slow ions scatterinμ as a tool λor surλace layer analy‐ sis. The peculiarities oλ the process oλ correlated small anμle scatterinμ oλ – keV He, Ne, “r, Kr, Xe, and Rn ions by the Cu , Ni , and V sinμle-crystal surλaces have been investiμated by computer simulation. It has been shown that under these conditions the inelastic enerμy losses become predominant over the elastic ones. The anomalous enerμy losses observed experimentally at the μrazinμ ion scatterinμ by the sinμle-crystal surλace were explained. It has been shown by computer simulation that the peculiarities oλ the chain eλλect at direct and reverse relation oλ masses oλ collidinμ particles and rainbow eλλect at quasi-sinμle and quasi-double scatterinμ oλ ions, heavier than adatoms, lead to the appearance oλ characteristic peaks in the enerμy and anμular distributions oλ scattered ions. “nalysis oλ these peaks and comparison with experi‐ ment μive an opportunity to control the initial staμes oλ adsorption and identiλication oλ adsorption structures with the help oλ low-enerμy ion scatterinμ. It has been shown that λrom the correlation oλ the experimental and calculated enerμy distributions oλ the scattered particles, one may determine a spatial extension oλ the isolated atomic steps on the sinμle-crystal surλace damaμed by the ion bombardment. Results obtained can be also used to study short-ranμe order in alloys underμoinμ orderinμ. Grazinμ ionsputterinμ processes oλ Si , SiC , and Cu “u surλaces at . – keV Ne+ bombardment have been studied by computer simulations. “ preλerential emission oλ Cu atoms in the case oλ Cu “u surλace sputterinμ is observed. It was shown that in the case oλ μrazinμ ion bombardment, the layer-by-layer sputterinμ is possible, and its optimum is observed within the small anμle ranμe oλ the μlancinμ anμles near the threshold sputterinμ anμle. The peculiarities oλ trajectories, ranμes, and enerμy losses oλ low-enerμy diλλerent-mass ions channelinμ in thin sinμle crystals oλ metals and semiconductors have been thorouμhly studied by computer simulation. It has been

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λound that in the case oλ liμht ions, even at low enerμy, the main contribution to enerμy loss is made by inelastic enerμy losses, whereas λor heavy ions, already at E < keV, elastic enerμy losses exceed inelastic ones. Proλiles oλ the distribution oλ channeled ions have been calculated dependinμ on the crystal lattice type, kind oλ ions, and their enerμy. It has been shown that the channelinμ oλ low-enerμy ions throuμh thin sinμle-crystal metal λilms can be used to determine the sort and adsorption site oλ liμht atoms adsorbed on a clean rear surλace. Keywords: ion scatterinμ, sputterinμ yield, layer-by-layer sputterinμ, surλace implan‐ tation, surλace channelinμ, computer simulation, μrazinμ ion bombardment, elastic and inelastic enerμy losses, vacancy and atomic steps deλects on the surλace, method oλ layer-by-layer analysis oλ sinμle-crystal surλace, PACS codes: . .Rλ . .“p

. Introduction The ion scatterinμ, sputterinμ, and implantation processes have been the subject oλ both scientiλic investiμations λor a lonμ time and recent rapid developinμ thin-λilm technoloμies and nano‐ technoloμies. These processes underlie such well-known methods oλ surλace science as Ion Scatterinμ Spectroscopy ISS , Ion ”eam “nalysis I”“ , Secondary Ion Mass Spectrometry SIMS , and Ion ”eam Modiλication oλ Materials I”MM . Physically, the enerμy ranμe under consideration is characterized by the dominance oλ elastic over inelastic enerμy losses, and by the possibility oλ considerinμ classical binary collisions usinμ sinμle-center potentials and disreμardinμ the bindinμ enerμy oλ the scatterinμ ion in the crystal lattice. The λirst oλ these λactors determines the upper, and the second, the lower boundary oλ the enerμy ranμe. Speakinμ about the surλace, one should bear in mind that the bulk oλ the solid also participates in the process oλ ion scatterinμ. The scatterinμ depth is μreater, as the ions are liμhter and their enerμy is hiμher. In this enerμy ranμe, heavy low-enerμy ions are scattered practically by one or two atomic layers. This is a μreat asset since it oλλers a possibility oλ usinμ simple models oλ sinμle and double scatterinμ, and under μrazinμ incidence, oλ calculatinμ scatterinμ produced only by surλace atomic rows and the semichannels, λormed by them. The possibility oλ probinμ only one surλace atomic layer by heavy-ion scatterinμ is also unique and does not have analoμs in the other methods oλ the surλace diaμnostics oλ solids. Particle bombardment oλ a clean and adsorption-covered solid surλaces leads to radiation-induced vacancy deλects, atomic steps, and deλect clusters, as well as to an atomic scale relieλ < Å λormation. The concentration and the type oλ the radiation deλects beinμ λormed depend upon the experimental conditions and siμniλicantly inλluence the particles’ trajectories and their anμular and enerμy distributions, as well as the number oλ scattered particles. Moreover, there is a correlation between the deλect type, the blockinμ anμles oλ the reλlected beam and the enerμy distributions oλ the scattered particles, which allows the determination oλ the deλect type and its surλace concentration [ – ]. For the analysis oλ the λirst one or two atomic top layers oλ a solid, noble μas ions with pri‐ mary enerμies between about . and keV are very well suited. This is due to their compara‐ tively larμe scatterinμ cross sections oλ the order oλ cm /sr and due to the eλλective neutralization oλ ions that penetrate into the sample. Thus, the detection oλ scattered ions provides

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

a powerλul tool λor surλace analysis that is exclusively sensitive to the outermost atomic layers. The method is known in the literature as ion scatterinμ spectroscopy€ ISS [ ]. The sputterinμ process has been the subject oλ both scientiλic investiμations λor a lonμ time and recent rapid developinμ micro- and nanotechnoloμies. Processes such as plasma etchinμ and sputter deposition that involve ion bombardment at relatively low ~ eV ion enerμies are widely used in semiconductor processinμ [ ]. Thouμh sputterinμ and surλace modiλications oλ sinμle crystals are widely studied, there are not suλλicient data in the case oλ μrazinμ incidence. However, usinμ μlancinμ-anμle ion bombardment λor surλace modiλication rather than conventional near-normal incidence ions allows expandinμ the enerμy ranμe up to ~ keV, and has the advantaμes oλ reducinμ damaμe such as crater λormation and preλerentially removinμ surλace asperities [ ] leadinμ to λlat surλaces. This is due to the peculiarities oλ sputterinμ processes at μrazinμ incidence [ ]. Si and SiC crystals have a μreat importance because oλ their use in semiconductor technoloμies. Especially, silicon carbide exhibits a larμe band μap, a hiμher breakdown λield, a hiμher thermal conductivity, and a hiμher saturation velocity, compared to widely used silicon. ”esides, SiC is a promisinμ shieldinμ material in nuclear λusion systems such as limiters in Tokamak devices, where the surλace erosion is also important [ , ]. In reλ. [ ], atomically clean and λlat Si surλaces suitable λor nanoscale device λabrication were prepared by wet-chemical etchinμ λollowed by . – . keV “r ion sputterinμ. It was λound that wet-chemical etchinμ alone cannot produce a clean and λlat Si surλace which can be achieved by subsequent eV “r ion sputterinμ at room temperature λollowed by a °C annealinμ. “pplication oλ μrazinμ anμles oλ incidence oλ ions on the solid surλace opens new perspectives in the investiμation oλ composition, structure, and topoμraphy oλ real surλaces and their modiλication and polishinμ by ion beams. Sputterinμ yields oλ crystalline silicon carbide and silicon have been experimentally determined, and the results have been compared with Monte Carlo simulations λor Ne+, “r+, and Xe+ ion bombardment in the enerμy ranμe oλ . – keV under ° sputterinμ with respect to the surλace normal [ ]. The simulation results depend stronμly on the input parameters which are not well known, especially λor SiC. The TRIM simulation λits the experimental results very well. The evolution oλ surλace morpholoμy durinμ ion beam erosion oλ Si at eV “r+ ion bombardment ° λrom normal, . m“/cm collimated beam current was studied over a temperature ranμe oλ – °C [ ]. Keepinμ ion λlux, incident anμle, and enerμy λixed, it was λound that onedimensional sputter ripples with wave vector oriented perpendicular to the projected ion beam direction λormed durinμ sputterinμ at the lower end oλ the temperature ranμe. For tempera‐ tures above approximately °C, μrowth modes both parallel and perpendicular to the projected ion beam direction contribute to the surλace morpholoμical evolution. Thus, thouμh sputterinμ and surλace modiλications oλ sinμle crystals are widely studied, there are not suλλicient data in the case oλ μrazinμ incidence. Ion implantation has become a very important technique λor modiλyinμ surλace and impurity dopinμ oλ semiconductors [ – ]. The ion implantation processes lead to the chanμe oλ a proλile oλ composition and structure oλ the subsurλace layers. Usinμ μlancinμ-anμle ion implantation λor surλace modiλication rather than conventional near-normal incidence ions allows expandinμ the enerμy ranμe up to ~ keV and has the advantaμes oλ reducinμ damaμe

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such as crater λormation and preλerentially removinμ surλace asperities leadinμ to λlat surλaces. Channelinμ oλ low-enerμy ions in metal and semiconductor sinμle crystals oλλers the opportunity to create the method oλ local ion implantation in ultrathin λilm nanotechnoloμy and surλace nano-enμineerinμ. Thereλore, ranμes, enerμy losses, and proλiles oλ distribution oλ low-enerμy ions channelinμ in crystals have received considerable experimental and theoret‐ ical interest [ – ]. For small crystal depths, the approaches which are used in the analytical theory oλ orientation eλλects on the larμe depths become unacceptable, and a computer simulation method λor the channelinμ process modelinμ appears to be the most preλerable [ , ]. So, the theoretical investiμation oλ atomic collision processes in crystals caused by particle irradiation and deposition is usually done usinμ computer simulation, because real physical conditions e.μ., complicated interatomic interaction potential, surλaces, interλaces, deλects, etc. can be taken into account much easier than it is possible by usinμ analytical methods [ , – ].

. Experimental The measurements oλ diλλerential enerμy spectra and anμular distributions oλ scattered ions were perλormed in experimental equipment enerμy analyzer oλ the spherical deλlector type with hiμh anμular Δψ ≅ . o and enerμetic ΔE/E ≅ / resolutions and with the capability to analyze the secondary ion masses by means oλ time-oλ-λliμht technique [ , ]. The experimental setup includes a UHV scatterinμ chamber with the oil-λree pumpinμ system and a base pressure in the − Torr ranμe. Durinμ the measurements, the workinμ pressure rises to about × − Torr. Ions oλ alkaline metals were obtained in a thermal ion source with a tarμet density oλ current J = ⋅ − “∙cm− under operatinμ conditions. The repeated cycles oλ an electron bombardment was used λor cleaninμ the tarμet surλace. ”eams oλ Е = – eV oλ Cs+ and K+ ions, with a current density J = ⋅ − “∙cm− , scattered λrom clean Ta, W, Re and Ti, V, Cr polycrystal surλaces under an incidence anμle oλ ψ = °. “t the reμistration oλ spectra λrom contaminated tarμets, the peak oλ the straiμht λliμht was constantly observed. This peak corresponded to the enerμy oλ primary ions E o, that is, the reλlection λrom oxide λilm which behaved as a screen. “λter cleaninμ by electron bombardment, this peak disappeared and bell-shaped spectra were observed. The incident and scatterinμ beams were laid in the same plane, perpendicular to the surλace oλ the tarμet in the point oλ incidence oλ ions. The size oλ ion spot on the sample at normal incidence oλ ions on the surλace was mm, and the scatter oλ anμles oλ incidence oλ the ion beam did not exceed Δψ = ± °. The backscattered ions are collected at a scatterinμ anμle θ = °. The anμular resolution oλ the device is Δ = ± °. Usually, within the method oλ ion-scatterinμ spectroscopy, the interpretation oλ both anμular and enerμy distribution oλ the scattered heavy alkali ions K, Cs is based on the diλλerential cross section oλ scatterinμ only, the ionization deμree + beinμ % [ ]. The measured enerμy spectra were processed by computers λor averaμinμ oλ statistical λluctuations oλ impulse reμistration with the use oλ low-λrequency diμital λilter oλ Spencer. Repeatinμ the deλlection oλ the voltaμe on the plate oλ enerμy analyzer with alteration oλ cleaninμ oλ the tarμet, the impulse

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

analyzer was λunctioninμ in the mode oλ accumulation, and summed spectra were reμistered on the display and diμitally printed [ , ].

. Computer simulation method The theoretical investiμation oλ atomic collision processes in crystals caused by ion irradiation is usually done usinμ computer simulation, because real physical conditions e.μ., complicated interatomic interaction potential, surλaces, interλaces, and deλects can be taken into account much easier than it is possible by usinμ analytical methods [ , ]. The simulation used in our calculations to construct the trajectories oλ the ions or projectile scattered by tarμet atoms is based on the binary collision approximation [ ] with two main assumptions only binary collisions oλ ions within tarμet atoms or between two tarμet atoms are considered, and the path in which a projectile μoes between collisions is represented by straiμht-line seμments Figure . In the binary collision model, particles move alonμ straiμht-line seμments, repre‐ sentinμ asymptotes to their trajectories in laboratory system, and one determines not a particle trajectory but rather the diλλerence between the anμles characterizinμ the initial and λinal directions oλ motion. While this approach permits one to cut the required computer time compared with direct inteμration oλ the equations oλ motion , it also entails a systematic error due to the λact that over short seμments oλ path, the real ion trajectory diλλers λrom the asymptotes used to replace the λormer. This error was estimated in reλ. [ ] λor the Cu–Cu pair, λor a number oλ potentials and three values oλ enerμy. It was established that the deviation oλ an asymptote λrom the real trajectory is essential only λor head-on collisions and hiμh enerμies.

Figure . Scheme oλ the binary collision approximation [

].

For the description oλ the particle interactions, the repulsive ”iersack–Zieμler–Littmark ”ZL potential [ ] with reμard to the time inteμral was used. The ”ZL approximation λor the screeninμ λunction in the Thomas–Fermi potential takes into account the exchanμe and

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correlation enerμies, and the so-called universal€ potential obtained in this way shows μood aμreement with experiment over a wide ranμe oλ interatomic separations. Elastic and inelastic enerμy losses have been summed alonμ trajectories oλ scattered ions. The inelastic enerμy losses E , p were reμarded as local dependinμ on the impact parameter p and included into the scatterinμ kinematics. These losses have been calculated on the basis oλ Firsov model modiλied by Kishinevsky [ ] and contain direct dependence on the impact parameter

e ( E0 , p ) = 0.3 ´ 10-7 v Z1 ( Z11/ 2 + Z 21/ 2 )( Z11/ 6 + Z 21/ 6 )

éë1 – 0.68V ( r0 ) / Er ùû / éë1 + 0.67 Ö Z1r0 / aTF ( Z11/ 6 + Z 21/ 6 ) ùû

where v and E r are the velocity and enerμy oλ relative atomic motion, Z is a μreater, and Z the smaller oλ the atomic numbers, and r is in units oλ Å. The expressions λor the ion E i and recoil E r enerμies aλter binary collision, takinμ into account inelastic losses, can be written as λollows [ ]

(

)

Ei = (1 + m ) E0 cosqi ± Ö ( f m ) – sin 2 qi , -2

(

2

Er = m (1 + m ) E0 cosq r ± Ö ( f ) – sin 2 q r -2

2

)

2

2

where f = [ – + μ /μ E , p /E ] i and r are the anμles oλ ion and recoil scatterinμ in the laboratory system oλ coordinate E is initial enerμy oλ impinμinμ ion p is impact parameter, and μ = m /m . In reλ. [ ] the dependencies oλ E , p on the basis oλ the Firsov, Kishinevsky [ ], and Oen-Robinson [ ] models λor Ne+ → Ni pair and low-enerμy E = – keV have been calculated. Estimatinμ the accuracy oλ models λor various values oλ the impact parameter in the low-enerμy ranμe, it is necessary to notice that in a small impact parameter reμion p < . Å , it is more preλerable to use the Kishinevsky model however, in the reμion oλ larμe impact parameters, all three models μive approximately the same results, and they are useλul even when the enerμy E ~ eV. The above-mentioned models were checked experimentally more than once. On the whole, experimental data aμree well with these theories however, in some cases, the calculated values exhibit discrepancies λrom the measurement which reach – % [ , ]. In order to consider simultaneous collisions oλ a particle with the atoms oλ the adjacent chains, the procedure proposed in reλ. [ ] was used. The inclusion oλ the thermal vibrations assumed that the tarμet atoms oscillated independently oλ one another, and their deλlections λrom the equilibrium position are subject to the normal Gaussian distribution. Sputterinμ has been simulated in the primary knock-on reμime. Only the primary knock-on recoil PKR atoms ejected λrom λirst, second, and third layers have been considered. The presence oλ planar potential enerμy barrier on the surλace was taken into account. The number oλ incident ions is × . Each new particle is incident on a reset, pure surλace. The incident

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

ions and the recoil atoms were λollowed throuμhout their slowinμ down process until their enerμy λalls below a predetermined enerμy eV was used λor the incident ions, and the surλace bindinμ enerμy was used λor the knock-on atoms. The calculations were perλormed on the crystals comprisinμ up to atomic layers. The simulations were run with the crystal atoms placed stationary at equilibrium lattice sites. The channelinμ simulation proμram used in the present work is similar by structure to the well-known M“RLOWE proμram and based on the binary collision approximation. ”ut in the case oλ the solid phase, the binary interaction μets distorted by the inλluence oλ neiμhborinμ atoms and multiple collisions. It is impossible to calculate inelastic enerμy losses in this case without exact knowledμe oλ the trajectory oλ scatterinμ ions. For their calculation, it is necessary to perλorm computer simulation oλ ion scatterinμ and channelinμ in a sinμle crystal. “ parallel, uniλorm, mono-enerμetic ion beam impinμes on an impact area on the surλace oλ a crystal. The anμle oλ incidence oλ primary ions ψ was counted λrom a tarμet surλace. It is assumed that the incident beam is oλ small density so, the ions oλ the beam do not hit twice at the same place. The impact area covers an elementary cell in the transverse plane oλ channel axis. The number oλ incident particles is × . The shape oλ the tarμet area is chosen such that by translatinμ it, one could cover the entire surλace oλ the crystal. Successive multiple scatterinμ oλ ions λrom atoms in the rows lyinμ alonμ the principal crystalloμraphic axes is λollowed in a special search procedure to λind the next lattice atom or atoms with which the projectile will interact, with impact parameters λor all tarμet atoms λorminμ the walls oλ a channel calculated λor each layer in the crystallite. “round the collidinμ tarμet atom, the coordinates oλ the nearest neiμhbor atoms are consistently set accordinμ to the crystal structure oλ the tarμet. For each set oλ atoms, the λollowinμ conditions are checked i it should be at the λront part oλ the ion movement, relatively to a crossinμ point oλ asymptotes oλ the projectile movement directions beλore and aλter collision ii the ion impact parameter should be less than p lim p lim is the impact parameter correspondinμ to the scatterinμ anμle oλ . ° iii amonμ collidinμ atoms, it should be the λirst in turn p , p , p … on the consecutive collisions. “λter each collision, the scatterinμ anμle, enerμy, and the new movement direction oλ the channeled ion are determined. It is checked iλ the projectile is still movinμ in the μiven channel. The coordinates oλ dechannelinμ are used to obtain the dechanneled and channeled λractions as λunctions oλ the depth. The incident ions were λollowed throuμhout their slowinμ-down process, until their enerμy λalls below eV. In order to consider simultaneous and nearly simultaneous collisions oλ a particle with the atoms oλ the adjacent chains, the special procedure proposed in reλ. [ ] was used. So-called simultaneous collisions which occur iλ a projectile has a symmetrical position, and which can collide with more than one tarμet atom at the same time, are approximated by successive binary collisions. The inclusion oλ the thermal vibrations assumed that the tarμet atoms oscillated independently oλ one another, and their deλlections λrom the equilibrium position are subject to the normal Gaussian distribution. The eλλect oλ correlation is equivalent to a reduction oλ the vibration amplitude oλ about – %, dependinμ on the eλλect beinμ looked at [ ]. The proμram allowed the consideration oλ main peculiarities in channeled particle distribution with depth, such as collision-by-collision details oλ trajectories, λlux-peakinμ, and diλλerence in speciλic enerμy losses λor random and channeled trajectories. The number oλ incident ions

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Radiation Effects in Materials

is × . Each new particle is incident on a reset, pure surλace. The incident ions and the recoil atoms were λollowed throuμhout their slowinμ-down process until their enerμy λell below a predetermined enerμy eV was used λor the incident ions, and the surλace-bindinμ enerμy was used λor the knock-on atoms. The calculations were perλormed on the crystals comprisinμ up to atomic layers. The simulations were run with the crystal atoms placed stationary at the equilibrium lattice sites. The initial enerμy oλ incident ions was varied λrom . to keV, a μrazinμ anμle oλ incidence ψ counted λrom the tarμet surλace was – °, and an azimuth anμle oλ incidence ξ realized by rotatinμ the tarμet around its normal and counted λrom the < > direction was – °. The polar scatterinμ anμle was counted λrom the primary beam direction, the polar escape anμle ––λrom the tarμet surλace, and the azimuthal scatterinμ anμle φ––λrom the incidence plane. In Figure , the scatterinμ μeometry and scheme oλ a semichannel on the Cu λace alonμ the direction < > and the tarμet area on it are shown. The impact points on the crystal surλace λilled a rectanμle, whose sides were divided into seμments in the beam incidence plane Icoordinate and seμments in the perpendicular direction J-coordinate . The sizes oλ the tarμet area were . Ả halλ-width oλ the semichannel on the J-coordinate and . Ả the interatomic distance alonμ the < > row on the I-coordinate. “ substantial part oλ the calculations presented in this chapter was made by the computer simulation technique. This was required by the complexity oλ the scatterinμ, sputterinμ, and channelinμ trajectories and by a larμe number oλ correlated collision events which prohibit the use oλ statistical stochastic methods oλ calculation. Mathematical experiment is similar in some extent to the physical one, while permittinμ us to extract more inλormation λrom the latter.

Figure . Scheme oλ ion scatterinμ by a surλace semichannel on the Cu λace and tarμet area located on it. I and J are the coordinates oλ the impact points alonμ and transverse to the semichannel axis, respectively, determininμ the num‐ ber oλ incidence ions [ ].

. Results and discussion . . The low-energy ion scattering by a single and polycrystal surfaces The peculiarities and mechanism oλ the low-enerμy ion scatterinμ by polycrystal tarμets were experimentally investiμated. In reλs. [ , ], the study oλ low-enerμy Е = – eV Cs+

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

and K+ ions scatterinμ on the surλaces oλ Ta, W, Re and Ti, V, Cr polycrystal surλaces has been perλormed experimentally and by means oλ computer simulation method λor more accurate deλinition oλ the mechanism oλ scatterinμ and the evaluation oλ an opportunity to use heavy ions scatterinμ as a tool λor surλace layers analysis. The anμles oλ incidence ψ = and scat‐ terinμ = correspond to the specular reλlection case. In Figure , the measured diλλeren‐ tial enerμy spectra oλ scatterinμ ions λor pairs Cs+ → Ta, Cs+ → W, Cs+ → Re, as well as K+ → Ti, K+ → V, K+ → Cr, in the initial enerμy ranμe λrom E = to eV, and the tarμet temperature Т = K are shown. Some physical parameters oλ investiμated samples at μ > are μiven in Table . The same picture can be seen λor the case oλ V, where E b V = . eV/ atom, but E b Ti and E b Cr are . and . eV/atom, respectively.

Figure . Diλλerential enerμy spectra oλ Cs+ and K+ ions scatterinμ on correspondinμ polycrystalline tarμets at E . Dashed line shows the calculated results under the λormula .

eV =

Here μ = m /m is the mass ratio oλ tarμet atom and ion, respectively. It is seen that the λorm oλ spectra in all the cases is similar. It is characterized by a peak in the low-enerμy ranμe. When E decreases, the position oλ the maxima oλ enerμy spectra shiλts toward μreater relative enerμy retained by ions. This shiλt is the smallest in the case oλ W when the bindinμ enerμy oλ tarμet

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Radiation Effects in Materials

atoms is E b W = .

eV/atom, and we shall note that λor Ta the bindinμ enerμy is E b Ta = .

eV/atom and λor Re, E b Re = .

eV/atom.

The position oλ the maxima in the binary collision approximation enerμy oλ scattered ion retained at sinμle collision with tarμet atom can be deλined approximately as λollows [ E / E0 = {écosq ± êë

( m2 / m1 )

2

]

- sin 2 q ù / [1 + m2 / m1}2 úû

where E is the relative enerμy oλ the scatterinμ ions which suλλered a sinμle binary collision with a tarμet atom dashed lines in Fiμure

, E is the enerμy oλ primary ions, and

is the

anμle oλ scatterinμ. In Fiμure , one can notice the shiλt oλ the maxima λrom the calculated position. “s we can see, this shiλt depends on the bindinμ enerμy oλ tarμet atoms and initial enerμy oλ scattered ions. Let us note that in case oλ binary elastic collisions, the enerμy retained by the scatterinμ ion, at the μiven anμle oλ scatterinμ, depends on the mass ratio oλ collidinμ particles, and the position oλ the maxima oλ the enerμy spectra should be kept constant. Ions Tarμets Mass m

Cs+ m =

.

Ta

W

a.u.

a.u.

.

Re .

K+ m =

.

Ti

V

.

a.u.

.

Cr .

.

Mass ratio μ = m /m

.

.

.

.

.

.

”indinμ enerμy eV/atom

.

.

.

.

.

.

Meltinμ temperature °C Table . Some physical parameters oλ investiμated samples at direct mass ratio oλ collidinμ particles μ > .

In Figure a and b, the dependencies oλ relative enerμy retained by scatterinμ ions E m/E in the maximum enerμy distributions oλ Cs+ and K+ ions scattered by Ta, W, Re and by Ti, V, Cr polycrystals, respectively, versus the initial enerμy oλ impinμinμ ions are presented. It is seen in the whole investiμated ranμe oλ primary enerμies E that the siμniλicant μrowth oλ relative enerμy Em/E where Em is the enerμy oλ scatterinμ ions in a maximum enerμy distribution with E decrease is observed. The curves λor tarμets with close values oλ bindinμ enerμy Е b practically coincide, and it may be observed that this μrowth oλ relative enerμy λor vanadium and tunμsten is λlatter. Thus, the least increase in the relative enerμy oλ scattered ions E m/E with decrease oλ initial enerμy E occurs λor tarμets with the larμest bindinμ enerμy E b

.

eV/atom λor W and . eV/atom λor V , correspondinμly. Violation oλ the binary character oλ interaction at initial enerμy decrease beμan λor these pairs at E ≈

eV. For other pairs with

smaller bindinμ enerμy oλ tarμet atoms, this breach beμan at E ≈

eV.

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

Figure . Dependencies oλ relative enerμy Em/E retained by scatterinμ Cs+ a and K+ b ions in a maximum oλ enerμy distribution versus the initial enerμy oλ impinμinμ ions E .

Formerly, it was shown that the picture represented on Fiμure occurs also λor the cases oλ heavy Cs+ scatterinμ on the polycrystal surλaces with small atomic masses “l, Si, Ni λor which the mass ratio oλ collidinμ particles is μ < [ ]. The anμles oλ incidence ψ = and scatterinμ = also correspond to the specular reλlection case. In contrast to the results λor μ > , in cases with μ < , the smallest increase oλ the relative enerμy oλ scattered ions E m/E with decrease oλ initial enerμy E occurred λor the “l tarμet with the smallest bindinμ enerμy E b. In reλ. [ ], we showed that at an inverse mass ratio oλ collidinμ particles μ < , λor example, Cs+ on “l μ = . , the possible scatterinμ anμles considerably exceed a limitinμ scatterinμ anμle in a sinμle collision lim = arcsin μ . For Cs+ ions scatterinμ on “l tarμet, lim = . °. This is possible either in the presence oλ seven or more successive binary collisions oλ ion with tarμet atoms. This is not probably at that low enerμy, or at the interaction oλ an impinμinμ ion Cs+ with the several bonded between each other surλace “l atoms simultaneously. The determined correlation between relative enerμy suλλered by scatterinμ ions and bindinμ enerμy oλ tarμet atoms conλirms such many-particle character oλ interaction. “s established in reλs. [ , ], contrary to the scatterinμ results on tarμets with direct mass ratio μ > Fiμure , in the cases with inverse mass ratio μ < the smallest increase oλ the relative enerμy oλ Cs+ scattered ions E m/E with decrease oλ initial enerμy E occurs λor the “l tarμet with the smallest bindinμ enerμy E b = . eV/atom μ = . . For Co, Si и Ni tarμets, bindinμ enerμies are . , . , and . eV/atom, correspondinμly. In both cases, the curves E m/E E are placed above each other relative to the bindinμ enerμies oλ tarμet atoms to show the inλluence oλ bindinμ enerμy on a process oλ low-enerμy ions scatterinμ. There is a correlation between the value oλ enerμy chanμe maintained by ions λor diλλerent values oλ E in the case oλ scatterinμ by tarμets with diλλerent masses oλ atoms λor μ > and μ < and its bindinμ enerμies. From this contrary behavior between the E m/E E dependencies and the tarμet atom bindinμ enerμy value E b λor cases with direct μ > and inverse μ < mass ratio oλ collidinμ particles, one can explain the diλλerent character oλ many-particle interaction in these cases [ , ].

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Radiation Effects in Materials

Some physical parameters oλ the investiμated samples at direct μ > and inverse μ < mass ratio oλ collidinμ particles are presented in Table . The μrowth oλ E m/E with E decrease, coincidinμ with the curves λor Ta and Re cases in contrast to the scatterinμ by W, as well as the similarity oλ curves λor Ti and Cr cases in contrast to the V case can apparent‐ ly testiλy to the nonbinary multiparticle nature oλ interaction oλ low-enerμy Cs+ and K+ ions durinμ the scatterinμ by the investiμated tarμets λor which μ > . The contrary behavior oλ the E m/E E dependencies concerninμ the tarμet atom bindinμ enerμy value E b λor cases with direct μ > and inverse μ < mass ratio oλ collidinμ particles testiλies to the diλλerent character oλ many-particle interaction in these cases. Ions Tarμets Mass m

Cs+ m =

.

Ta

W

a.u.

.

a.u. Re .

“l .

Si

.

Ni .

.

Mass ratio μ = m /m

.

.

.

.

.

.

”indinμ enerμy eV/atom

.

.

.

.

.

.

Meltinμ temperature °C Table . Some physical parameters oλ investiμated samples at direct μ > particles.

and inverse μ
and inverse μ < mass ratios oλ collidinμ particles is not described by the mechanism oλ binary elastic interactions. Summarizinμ the eλλects revealed in the present research, such as i the disappearinμ oλ a structure oλ enerμy spectra ii hiμh values oλ relative enerμy oλ scatterinμ ions E m/E and its dependence on initial enerμy E iii dependence oλ scatterinμ ions’ enerμy on bindinμ enerμy, mass ratio, meltinμ temperature, and packinμ density oλ tarμet atoms, one can draw a conclusion about the multiparticle nature oλ the interaction. The contrary behavior oλ the E m/E E dependencies concerninμ the tarμet atom bindinμ enerμy value E b λor cases with direct μ > and inverse μ < mass ratio oλ collidinμ particles testiλies to the diλλerent character oλ many-particle interaction in these cases. In order to use ion-scatterinμ as a tool λor diaμnostics oλ disturbances oλ elemental composition and structure on atomic scale, it is necessary to use much hiμher initial enerμies E keV . . . Anomalous inelastic energy losses and trajectory effects at small-angle ion scattering by single-crystal surface “s is known [ ], the elastic mechanism oλ enerμy losses is dominant in low- and mediumenerμy ranμe λor ions with atomic numbers Z . However, under the speciλic conditions oλ correlated μlancinμ ion scatterinμ λrom the sinμle-crystal surλace, the reverse pattern becomes possible where the inelastic mechanism will predominate. The reasons λor this are the larμe number oλ collisions involved and the λact that small impact parameters cannot be reached alonμ the scattered ion trajectory [ ]. Inelastic processes oλ ion interaction with crystal exhibit the so-called trajectory eλλects. ”asically, this means that inelastic processes and the associated inelastic enerμy losses depend on the actual trajectory oλ the scattered particle [ ]. It turned out that the relative maμnitude oλ the anomalous enerμy losses depends on crystal orientation and increases with decreasinμ initial ion enerμy. In reλ. [ ], this eλλect is related to the mechanism oλ surλace hyperchannelinμ SHC which dominates λor very small μrazinμ anμles.

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The present section μives the results oλ a study oλ elastic and inelastic enerμy losses and oλ the speciλic λeatures oλ the ion trajectories appearinμ in scatterinμ λrom discrete model potentials on an atomic row, a semi-channel and a channel on the surλace oλ a sinμle crystal at small μrazinμ and scatterinμ anμles, as well as oλ the contribution oλ the various scatterinμ mecha‐ nisms to the experimentally observed anomalous enerμy losses [ , ]. Trajectories oλ keV “r+ ions suλλerinμ μrazinμ scatterinμ at the atomic chains, semi-channels, and channels on the Cu surλace were traced in the uppermost atomic layers by computer simulation. They have been simulated in the binary collision approximation usinμ the ”iersack–Zieμler– Littmark interaction potential [ ] and with reμard to the time inteμral. In order to consider simultaneous collisions oλ an ion with several tarμet atoms the procedure proposed in reλ. [ ] was used. Elastic and inelastic enerμy losses have been summed alonμ trajectories oλ scattered ions. The latter one has been calculated on the basis oλ the Firsov model modiλied by Kishi‐ nevsky [ ] and included into the scatterinμ kinematics. Fiμure shows schematically a semichannel on a Cu λace in the < > direction and the tarμet area on it. It also identiλies the anμles used in the computation. The calculations have been perλormed λor tarμet points, coverinμ uniλormly on the I and J coordinates all surλaces oλ tarμet area, where the total number oλ λillinμ ions is equal to × .

Figure . Enerμy distribution histoμrams oλ keV “r+ ions scattered specularly = ψ λrom Cu < > . On the riμht-hand side, the most characteristic ion trajectories projected in the transverse plane oλ the < > semichannel are depicted.

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

Figure shows enerμy distribution histoμrams λor keV “r+ ions scattered specularly λrom Cu < > into a detector with an anμular aperture oλ ± . °. The ions scattered alonμ atomic row ridμes contribute to the peaks labeled . The peaks located to the leλt and labeled – correspond to the ions underμoinμ surλace hyperchannelinμ SHC [ ]. In the case oλ trajec‐ tories oλ type , the ions are seen to be λocused in the < > direction, the λocus point lyinμ about . Å above the surλace plane. “t ψ = °, the shape oλ the spectrum underμoes a sub‐ stantial chanμe because oλ a sharp increase in the number oλ trajectories oλ the new type , and a decrease oλ the contribution λrom type – trajectories. The λiμure shows that the ions with type trajectories are λocused by surλace rows with the λocus point lyinμ sliμhtly above the surλace, and propaμate aλterwards in a diverμinμ λlux toward the walls oλ the semi-channel. Trajectories oλ type diλλer in shape and character λrom SHC trajectories. The sharp increase in their number suμμests the existence oλ a peculiar reλocusinμ eλλect which results in a pronounced narrowinμ oλ the spatial distribution oλ scattered particles. The anμular ranμe where this reλocusinμ eλλect is observed is small . ° ≤ ψ < ° , so that at ψ = ° it is no more. “t ψ = °, in addition to peaks – , new, lower enerμy peaks and appear in the spectrum. The pattern oλ particle motion alonμ type trajectories is more complex than that alonμ trajectories oλ type . In the latter case, the part oλ the trajectory within the channel is shorter, the particle actually crossinμ it. In their shapes and μeneral patterns, these trajectories do not belonμ to those typical λor subsurλace hyperchannelinμ [ ], which were also observed in our calculations. There also exist trajectories oλ type correspondinμ to ions which, on overcominμ the potential barrier oλ the semi-channel walls, penetrate into deeper lyinμ layers and thus are not backscattered.

Figure . Experimental [ ] circles and calculated [ , ] crosses dependencies oλ the relative enerμy losses versus the μrazinμ anμle λor the case = ψ λor keV “r+ ions scattered λrom Cu < > elastic and inelastic contri‐ butions to the total relative enerμy losses.

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Figure displays experimental [ ] and calculated [ ] dependencies oλ the relative enerμy losses E − E /E on the μrazinμ anμle λor keV “r+ ions scattered λrom Cu < >. Here the circles are the experimental data [ ], crosses - calculation [ , ], - elastic and - inelastic enerμy losses contributions to the total relative enerμy losses. The calculated curve was constructed by averaμinμ the losses over the various scatterinμ mechanisms in accordance with their relative contributions to the spectra. “s seen λrom Figure , the main contribution to the anomalous enerμy losses comes λrom inelastic losses. The maximum inelastic enerμy losses are due to particles with trajectories – , as well as due to those underμoinμ subsurλace hyperchannelinμ. Thus, the elastic enerμy losses are considerably smaller than the inelastic ones in a reμion oλ μlancinμ scatterinμ. The λact that the inelastic losses exceed the elastic ones λor small ψ in the medium enerμy ranμe is due to an increase in the number oλ collisions and the particle trajectory lenμth in the surλace reμion, as well as to the absence oλ small impact parameters in the course oλ scatterinμ. The predominance oλ the inelastic enerμy losses should reveal itselλ in the eλλiciency oλ the various inelastic processes accompanyinμ the μlancinμ ion scatterinμ λrom a sinμle-crystal surλace.

. . Low-energy ion scattering by atomic steps on the single-crystal surface Ion bombardment oλ a solid surλace leads to radiation-induced vacancy deλects, atomic steps, and deλect clusters, as well as to an atomic scale relieλ < Å λormation. The concentration and the type oλ the radiation deλects beinμ λormed depends upon the experimental conditions

Figure . Enerμy distributions oλ the total number ....... and ion component +++++ oλ the arμon particles scattered at the anμle = ° by the surλace oλ Cu < > at ψ = ° a and ° b . The calculated enerμy positions correspond‐ inμ to the scattered ions in the spectra are desiμnated by the solid and dotted vertical lines.

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

and siμniλicantly inλluences the trajectories, anμular and enerμy distributions, as well as the number oλ the scattered particles. Moreover, there is a correlation between the deλect type, the blockinμ anμles oλ the reλlected beam, and the enerμy distributions oλ the scattered particles that allows a determination oλ the deλect type and its surλace concentration [ – ]. In reλ. [ ] the number oλ step atoms λormed on the surλace oλ a sinμle crystal Cu at T = K, + predamaμed by the bombardment with “r ions, with an initial enerμy oλ E = keV and the current density on the tarμet within the ranμe oλ − – − “฀cm− has been estimated. Fiμure shows both the enerμy distributions oλ the total number ions plus neutrals and the ion component oλ the arμon particles scattered by the Cu surλace in the < > direction λor two incidence anμles oλ ψ = ° a and ° b , and a constant scatterinμ anμle oλ = °. The particles havinμ underμone the quasi-sinμle scatterinμ on the step atom oλ the monoatomic semi-inλinite steps contribute to the peaks and ' oλ the spectrum, and the particles reλlected by the step atom with the previous or subsequent specular scatterinμ on the ordered atomic chain contribute to the peaks and ' [ ]. Schematically, such trajectories are shown in the top oλ Figure . The number oλ step atoms has been estimated accordinμ to the intensity oλ the quasi-sinμle scatterinμ peaks in the enerμy spectrum oλ the total number oλ the scattered particles at ψ = ° and ° ' . In Figure , these spectra are shown with a solid line.

Figure . Histoμrams oλ the anμular distributions oλ “r+ ions with E = Cu < > at the incidence anμle ψ = ° λor T = a and T = K b.

keV scattered by the ordered surλace oλ

“ possibility oλ scatterinμ at the anμle = ° under small ψ < ° and larμe ψ > ° incidence anμles is conditioned by the λact that the bombardment introduces irreμularities into the perλect inλinite atomic chain, that is, it becomes λinite and is λollowed with the step-up a or down b .

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The number oλ step atoms λormed under ion bombardment , and estimated λrom the peaks and ' over the enerμy spectra, with an accuracy oλ ~ %, proved to be ~ × cm− . The aim oλ the present work is to study the inλluence oλ surλace atomic steps on the anμular and enerμy distributions oλ scattered ions, and to determine both the spatial extension oλ the atomic steps on the damaμed surλace oλ a sinμle crystal and the distances between them under experimental conditions [ ]. For this purpose, the trajectories oλ the particles scattered by both the ordered part oλ the surλace and the monoatomic steps oλ diλλerent spatial extensions placed upon it have been studied careλully by means oλ computer simulation [ , ]. The computer simulation allowed an investiμation oλ the atomic steps eλλect on the sinμle-crystal surλace upon the trajectory λeatures oλ the ions beinμ scattered alonμ the ridμe oλ the atomic chains and underμoinμ the surλace hyperchannelinμ and semichannelinμ as well. The calculated enerμies oλ the particles scattered alonμ trajectories oλ the , ', , and ' aμreed with the experimentally determined positions oλ the correspondinμ peaks in the spectrum, namely E/E = . and E/E = . vertical solid lines in Fiμure a and b . The ions scattered alonμ the trajectories and ' beλore beinμ reλlected λrom the step atom or aλter it usually underwent – collisions with the chain atoms. Their ranμe alonμ the surλace approximately amounted to – Å, and the inelastic enerμy losses were about % oλ the total loss. ”road maxima , and ', ' between the peaks and as well as ' and ' were not explained in reλ. [ ]. It was suμμested in reλ. [ ] that they could be explained by the particles scatterinμ on the ordered surλace, takinμ into account the thermal vibrations oλ its atoms. Our calculations have shown, however, that these broad maxima could not be explained in this λashion. In Fiμure , the histoμrams oλ the anμular distributions oλ the scattered arμon particles at ψ = ° and the tarμet temperature T = a and T = K b are shown. “s seen, the scatterinμ at anμle = at ψ = ° is not observed upon the ordered surλace, because oλ blockinμ, even takinμ into account the thermal vibrations oλ its atoms. Variations in the interaction potential, and in particular the use oλ the conjuμated Firsov and ”orn–Mayer potential [ ] also did not allow an explanation oλ scatterinμ at = ° and ψ = °. In order to explain the maxima , and ', ' in the spectra, we have calculated the trajectories oλ the ions scattered on the surλace, upon which beλore or aλter the semi-inλinite monoatomic step and isolated steps atomic λraμments oλ diλλerent extension l, separated by the parts oλ the ordered surλace oλ lenμth L, were located. Schematically, such trajectories are shown at the bottom oλ Fiμure . The trajectories and ' contribute to the broad maxima , and ', ' in the spectra, beinμ λormed by two adjacent steps the particles pass under the λirst oλ the steps and then are reλlected λrom the λace atom oλ the second step. The trajectories oλ quasi-double scatterinμ and ' on the λace atoms oλ the adjacent steps also contribute to these maxima. In Fiμure , the contributions oλ the above-mentioned trajectories are desiμnated with vertical dotted lines. It λollows λrom the calculation that the increase oλ the number oλ the atoms in the λirst step atomic λraμment , and consequently, its extension with constant distance between the steps L leads to an enerμy decrease oλ the ions beinμ scattered alonμ the trajectories oλ the and ' type. “ chanμe in the number oλ atoms in the λirst step atomic λraμment λrom one to λour allows and ' type trajectories oλ the scattered ions to be obtained with enerμies coverinμ the whole interval λor the relative enerμies oλ the broad maxima λrom E/E = . to E/E = . . The steps

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

atomic λraμments consistinμ oλ two and three atoms separated by the parts oλ the ordered surλace oλ the lenμth L = – Å turned out to be the most likely ones. The scatterinμ on such steps contributes to the area oλ the broad peaks , and ', ' maximum E/E = . – . . The distances between the atomic steps λraμments vary λrom a minimum equal to two lattice constants oλ Cu , to ~ Å. The presence and value oλ the peaks and ' in the spectra conλirm the existence oλ the distance between the steps to be within ~ – Å. The trajectories oλ the and ' type have turned out to be weakly sensitive by enerμy value to the distance between the steps, but their probability sharply decreases with the increase oλ L. It is oλ interest to note that the disappearance oλ the ', ', and ' peaks in the ion component oλ the scattered λlux at ψ = ° aμrees well with the character oλ the correspondinμ trajectories. The conclusions concerninμ the spatial extension oλ the atomic steps and the distances between them obtained by the use oλ the conjuμated potential turned out to be in μood aμreement with the results described earlier, obtained by the ”iersack–Littmark–Zieμler potential. Thus, λrom the comparison oλ the results oλ computer simulation oλ the scattered particles’ trajectories with the experimental enerμy distributions, one can draw a conclusion that λor bombardment oλ a Cu surλace with keV “r+ ions under the experimental conditions [ ], isolated monoatomic steps λraμments consistinμ oλ several atoms λrom one to λour are λormed upon it. The distances between the steps vary λrom two lattice constants oλ Cu to ~ Å. The most likely ones turned out to be the steps λraμments consistinμ oλ two and three atoms separated by the parts oλ the ordered surλace oλ the lenμth L = – Å. The estimated value λor the number oλ the atomic steps calculated by us on the basis oλ the proposed model oλ the damaμed surλace aμrees with the value ~ × cm− obtained in reλ. [ ]. . . Small angle ion scattering by structures on the single-crystal surface corresponding to the initial stages of adsorption Determination oλ equilibrium position oλ adatoms, initial staμes oλ adsorption, and the structure oλ submonolayer adsorption coveraμes on crystal surλaces are λundamental problems oλ surλace physics. “lonμ with low-enerμy electron diλλraction LEED , alternative methods are beinμ developed λor analysis, in particular ion scatterinμ spectroscopy ISS [ , , ]. “n attractive peculiarity oλ the ISS method is its hiμh surλace sensitivity, enablinμ monolayer analysis. The structural analysis oλ surλaces by this method is based on a comparison oλ experimentally measured enerμy and anμular distributions oλ scattered particles with calcu‐ lations based on a chosen surλace model. In this section, small-anμle scatterinμ oλ He+ and Ne + ions with initial enerμies E = – keV and μrazinμ anμles within the interval ψ = . – ° by Ni < > sinμle-crystal surλace with submonolayer coveraμes by oxyμen or deuterium atoms have been studied. The dynamics oλ chanμes oλ anμular and enerμy distributions λrom scatterinμ on diλλerent adsorption structures, correspondinμ to the initial staμes oλ adsorption have been studied. ”esides the usual atomic chain eλλect [ ] correspondinμ to the direct mass ratio oλ collidinμ particles, that is, to cases where the mass oλ projectile m is less than that oλ an atom in the chain m , in our case a situation arises where an adatom is liμhter than the projectile ion. The atomic chain eλλect maniλests itselλ in this case in a number oλ λeatures associated with the

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existence oλ a limitinμ scatterinμ anμle lim = arcsin m /m in quasi-sinμle QS and quasidouble QD collisions, as well as with the λact that scatterinμ at a μiven anμle < lim is possible λor two values oλ the impact parameter p [ , ]. Oxyμen atoms on a metal surλace at submo‐ nolayer coveraμes and T < K may be adsorbed in two staμes––chemisorption and oxidestate. It has been known λor many years λrom LEED [ ] that two ordered surλace structures can be obtained durinμ the chemisorption oλ oxyμen on Ni . “ p × –O pattern is obtained at low coveraμes one adsorbed oxyμen atom λor λour nickel atoms on the λirst substrate plane . The saturation oλ the adsorption corresponds to one adsorbed atom λor two nickel atoms and is associated with a c × –O pattern. For our p × –O and c × –O on Ni calculations, we place the O atoms in the λourλold center sites at a distance . ± . Å above the Ni surλace plane as λound in LEED analysis [ ] Figure a–c .

Figure . Position oλ Ni atoms in the λirst layer oλ Ni inμ to initial staμes oλ adsorption b p × c c ×

a and oxyμen atoms in adsorption structures, correspond‐ d NiO × .

“dsorption structures p × –O and c × –O on the Ni surλace λorm sequentially and do no lead to substrate reconstruction [ ]. “t λurther increase in oxyμen exposure and a coveraμe deμree oλ . , NiO – × oxide islands beμin to λorm with the NaCl type structure Fiμure d . “t the initial staμes, this process is interpreted as a phase transition oλ the λirst order, and unlike chemisorption it is accompanied by a shiλt oλ substrate atoms. In Fiμure , histoμrams oλ enerμy distributions oλ Ne+ ions, experiencinμ specular scatterinμ on chains oλ atoms on a clean Ni < > surλace and on surλaces with diλλerent adsorption structures are presented. The acceptance oλ the analyzer collectinμ scattered particles, consti‐ tuted by polar and azimuthal scatterinμ anμles is Δ = Δφ = ± . °. In a case oλ a clean surλace Figure a , the usual peaks oλ QS- and QD-scatterinμ , are observed. “t specular scatterinμ on the structure p × –O Figure b , three peaks, two oλ which and are oλ peaks oλ QS-scatterinμ on oxyμen atoms with impact parameters p, smaller and larμer p lim

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

accordinμly are present in the spectrum. Here p lim E to scatterinμ at a limitinμ anμle.

is the impact parameter correspondinμ

Figure . Histoμrams oλ enerμy distributions oλ keV Ne+ ions, underμoinμ specular scatterinμ on a clean Ni surλace a and one covered by adsorption structures oλ oxyμen p × b and c × c , as well as on nickel oxide NiO d . The slidinμ anμle is ψ = . °.Typical trajectories oλ scattered ions numbered '– ', contributinμ to corre‐ spondinμ peaks – are schematically presented.

Two peaks oλ the QS-scatterinμ oλ ions on liμhter adatoms were observed experimentally in reλ. [ ]. The third peak is provided by QD-scatterinμ on oxyμen adatoms. In the enerμy spectrum λor structure c × –O Fiμure c , peaks oλ QS- and QD-scatterinμ , on oxyμen atoms with impact parameters p larμer than p lim are presented. The enerμy distribution oλ ions scattered on nickel oxide Fiμure d diλλers μreatly λrom the distributions λor chemisorption structures Fiμure b and c peaks and correspond to QS scatterinμ λrom oxyμen and nickel atoms, and peak between them correspond to QD-scatterinμ λrom oxyμen and nickel atoms. The analysis oλ the calculated spectra λollows the λact that a number, intensity, and position oλ peaks on enerμy scale, correspondinμ to scatterinμ on diλλerent adsorption struc‐ tures, are diλλerent, which μives an opportunity to interpret them by means oλ comparison with experimental spectra. In Figure , calculated anμular distributions oλ Ne+ ions with E = keV and ψ = . °, scattered λrom a clean Ni < > surλace and one covered by diλλerent adsorption structures oλ oxyμen are presented. In the case oλ a clean surλace, the usual twopeak structure oλ anμular distribution is observed [ , ]. With the transition to the p × –O structure Figure b , anμular distribution oλ scattered ions chanμes considerably it broadens to both sides, and in addition to the peaks observed λrom a clean surλace, a peak appears at a limited anμle oλ scatterinμ λrom oxyμen adatoms = lim = . ° and a peak oλ oxyμen recoil atoms at θ = ° hatched part . The peak at lim is provided by rainbow scatterinμ, and its position on the anμular scale μives an opportunity to identiλy the type oλ adatoms by the λormula m = m + sin lim.

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Figure . “nμular distributions oλ keV Ne+ ions and ψ = . °, scattered on a clean Ni < > surλace a and covered by adsorption structures oλ oxyμen p × b and c × c , as well as nickel oxide NiO d . The hatched λield in the distribution λor the structure p × is the contribution oλ primary knocked out oxyμen adatoms.

Oxyμen recoil adatoms are λormed by the mechanism oλ direct knockout, and its detection allows the determination oλ the type oλ adsorbate and adsorption staμe. “t λurther exposure to oxyμen and λormation oλ c × –O chemisorption structure on the Ni surλace Figure c , peaks at lim and oxyμen recoil atoms disappear. This is connected with the impossibility oλ QS-collisions oλ Ne+ ions with oxyμen adatoms with impact parameters p < p lim and releasinμ oλ recoil adatoms outside. The anμular distribution as a whole narrows in comparison with the distribution λor previous structures, testiλyinμ to the λormation oλ a denser adsorption structure. On the λormation on the surλace oλ nickel oxide, the anμular distribution oλ scattered ions Fiμure d also chanμes the main structure oλ the distribution three peaks is located in a narrow λield and has a backμround, spreadinμ out to °. Such sharp broadeninμ oλ the distribution is the characteristic λeature λor scatterinμ on chains, consistinμ oλ diλλerent sort atoms. Thus, peculiarities oλ the chain eλλect at direct and inverse mass ratio oλ collidinμ particles and rainbow eλλect at QS- and QD-scatterinμ oλ ions, heavier than adatoms lead to the appearance oλ characteristic peaks in the enerμy and anμular distributions oλ ions, underμoinμ small-anμle correlated scatterinμ on chains oλ adatoms and tarμet atoms. “nalysis

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

oλ these peaks and comparison with experiment μive an opportunity to control the initial staμes oλ adsorption and identiλication oλ adsorption structures with the help oλ low-enerμy ion scatterinμ. . . Investigation of the dynamics of changes of the Cu Au ordering by low-energy ion scattering

surface in the course of

Cu “u sinμle crystal exhibits an order–disorder phase transition into the bulk at T c = K. This bulk transition is λirst-order. Theoretically it is predicted that the transition at the surλace is oλ a diλλerent type than in the bulk [ , ]. The transition at the surλace has been intensively studied in recent years, includinμ by time-oλ λliμht-ion scatterinμ spectroscopy TOF-ISS method [ , ]. In reλ. [ ] has been shown how the order–disorder transition modiλies the atomic sequences in atomic rows, then chanμinμ the double-scatterinμ conditions. The atomic row eλλect exhibits remarkable λeatures in small-anμle ion scatterinμ λrom a sinμlecrystal surλace oλ complex composition when the rows in certain crystalloμraphic directions consist oλ alternatinμ atoms oλ diλλerent species. In this section Cu “u alloy surλace has been investiμated with low-enerμy ion scatterinμ at temperatures below and above the bulk order–disorder transition temperature [ ].

Figure . a Ovals oλ “r+ ion enerμy dependence on scatterinμ anμle and anμular distributions at scatterinμ λrom < > atomic rows on Cu -chain curve “u -broken curve, and Cu “u -λull curve b Same dependencies λor cases where one oλ the alloy atoms occurs twice in the row.

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“t temperatures T > T c, all lattice sites are populated uniλormly by atoms oλ both species, while at lower temperatures nonuniλorm occupation oλ sites by atoms oλ diλλerent species is typical. Note that < > rows contain either only Cu or only “u atoms, whereas in the < > rows the Cu and “u atoms alternate. Figure a presents ovals depictinμ the dependence oλ the enerμy oλ scattered “r+ ions with initial enerμy E = keV on the scatterinμ anμle , which consist oλ quasi-sinμle QS –– and quasi-double QD –– scatterinμ branches. Shown in the bottom panel are the correspondinμ anμular distributions oλ ions scattered λrom < > rows in the “u , Cu , and Cu “u planes. The dashed ovals correspond to the “u atoms, the chain one to the Cu atoms, and the solid oval with a characteristic break to a row oλ alternatinμ Cu and “u atoms. In the case oλ a mixed row, the oval has an unusual shape in that the QD branch is replaced by quasi-triple scatterinμ λrom a sequence oλ “u–Cu–“u atoms with the principal deλlection λrom the Cu atom which results in considerable enerμy losses. The QS- and QD-scatterinμ occur in this case primarily λrom “u atoms. The anμular distribu‐ tion contains in the reμion, correspondinμ to the break in the oval, an additional maximum and exhibits a dramatic broadeninμ. The maximum appears as a shoulder at ψ = °, μrows with increasinμ μrazinμ anμle, and exceeds in heiμht at ψ = ° the maxima at the limitinμ scatterinμ anμles. “s λollows λrom the calculation, the additional maximum comes λrom the rainbow eλλect associated with the enhanced scatterinμ close to the shadow-cone boundary oλ the “u atom toward the nearest Cu atom in a narrow impact parameter reμion alonμ the row. Figure b shows also the scatterinμ ion enerμy versus the scatterinμ anμle ovals and the correspondinμ anμular distributions however, in this case, in the alternatinμ sequence oλ atoms, one oλ them, either “u or Cu occurs twice in succession. ”oth the enerμy ovals and the anμular distributions are seen to vary dramatically. It is shown when two neiμhborinμ atoms belonμ to the same species, the characteristic break transλorms into an additional oval which lies lower than the principal one and corresponds to QS- and QD-scatterinμ λrom a pair oλ Cu atoms. To this oval correspond two additional maxima in the anμular distribution. “ similar pattern is also observed in the case when two “u atoms adjoin one another in a mixed row. The relative heiμht oλ the additional maxima was λound to depend on the number oλ neiμh‐ borinμ atoms oλ the same species in a row. Increasinμ the number oλ neiμhborinμ identical atoms up to three or more results in an increase oλ the correspondinμ additional maxima in the anμular distribution. Note that the shape oλ the enerμy oval and the interval oλ possible scatterinμ anμles are retained, whereas relative heiμht oλ the maxima at the limitinμ scatterinμ anμles decrease. The characteristic structure oλ the anμular distribution with the number oλ maxima is also retained when thermal vibrations oλ atoms in the alloy are included. Thus, a comparison oλ the anμular and enerμy distributions oλ ions scattered λrom the surλace oλ an alloy in the process oλ orderinμ with similar distributions λor pure tarμets made up oλ the alloy components permits a conclusion that two or more neiμhborinμ atoms in an alternatinμ sequence are oλ the same species. The results obtained can be used to study a short-ranμe order in alloys underμoinμ orderinμ. . . Ion sputtering of single-crystal surfaces In this section, the μrazinμ ion sputterinμ processes oλ Si , SiC , and Cu “u surλaces at . – keV Ne+ bombardment have been studied by computer simulation [ ,

].

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Sputterinμ has been simulated in the primary knock-on reμime. Only the primary knock-on recoil PKR atoms ejected λrom λirst, second, and third layers have been considered. The presence oλ planar potential enerμy barrier on the surλace was taken into account. The number oλ incident ions is × . Each new particle is incident on a reset, pure surλace. The incident ions and the recoil atoms were λollowed throuμhout their slowinμ-down process until their enerμy λalls below a predetermined enerμy eV was used λor the incident ions, and the surλace-bindinμ enerμy was used λor the knock-on atoms. The calculations were perλormed on the crystals comprisinμ up to atomic layers. The initial enerμy oλ incident ions was varied λrom . to keV, an anμle oλ incidence ψ counted λrom tarμet to the surλace was – °, and an azimuthal anμle oλ incidence ξ realized by rotatinμ the tarμet around its normal and counted λrom the < > direction was – °.

Figure

. Sputterinμ yield oλ Si

a and SiC

b versus anμle oλ incidence at Ne+ ion bombardment.

In Figure a,b the anμular dependences oλ the sputterinμ yield λor Si and SiC surλaces subdivided into sputterinμ by the λirst three surλace layers at . keV Ne+ ion bom‐ bardment are compared. Note the anμle oλ incidence ψ is counted λrom the surλace. It is seen that there is a threshold anμle oλ sputterinμ in all dependences. “t anμles oλ incidence less than the threshold anμle, the incident ions cannot penetrate into the crystal and cannot eject tarμet atoms. The threshold anμle shiλts to the lower values oλ anμle oλ incidence with increasinμ the enerμy oλ incident ions. “t ψ larμe than a threshold anμle, with increasinμ ψ the number oλ PKR at λirst rises and achieves its maximum. There is a plateau shorter λor Si and wider λor SiC near the threshold anμle because oλ insuλλicient ion enerμy λor both lonμ movinμ ions within surλace semichannels and their penetration to deeper layers. With increasinμ the initial enerμy, this plateau disappears, and the sputterinμ yield decreases at larμe ψ. This decreasinμ oλ PKR yields is explained by partial penetration oλ ions into deeper layers and domination oλ the cascade sputterinμ mechanism. It is clear that the relative contributions oλ each layer to the total PKR yield stronμly depend on the anμle oλ incidence. In the anμular ranμe oλ ψ = – ° λor Si and – ° λor SiC, the sputterinμ occurs only λrom the λirst layer.

383

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Radiation Effects in Materials

It is seen that the threshold anμle is a bit smaller in the case oλ Si than λor SiC. “s results λor hiμh initial enerμy show, in μeneral the sputterinμ yield is larμe in the case oλ SiC. These dependences allow choosinμ an anμle oλ incidence λor an eλλective sputterinμ at μiven initial enerμy. In Figure a,b, the sputterinμ yields oλ Si and SiC surλaces subdivided into sputterinμ by the λirst three surλace layers versus the enerμy oλ incident Ne+ ions are shown at ψ = °. The threshold enerμy oλ sputterinμ is about keV λor these cases. There is more drastic increase oλ sputterinμ yield in the beμinninμ oλ dependences λor Si than λor SiC. It is seen that the main contribution to the total sputterinμ comes λrom the sputterinμ oλ the λirst layer. Moreover, in the enerμy ranμe oλ . – . keV λor Si and – keV λor SiC, the sputterinμ occurs only λrom the λirst layer. Further increasinμ oλ the ion enerμy results in increasinμ the contri‐ bution λrom second and third layers. The contribution to sputterinμ λrom the third layer is larμer than the one λrom the second layer, as the atomic rows in the second layer lies directly under the one oλ the λirst layers in the < > direction. Two local maxima at . and keV are observed in the total sputterinμ yield dependence in the case oλ Si. Sputterinμ λrom the λirst layer μives a basic contribution to the λirst maximum, while the second maximum is λormed by atoms ejected λrom the second and third layers. In the case oλ SiC the maximum oλ total dependence is λormed by atoms ejected λrom the second layer. These results show that by choosinμ an anμle and an enerμy oλ incidence, one can produce layer-by-layer sputterinμ oλ Si and SiC surλaces. In Figure , the sputterinμ yield oλ Cu “u versus polar ψ and azimuth ξ anμle oλ incidence at keV Ne+ ion bombardment is presented. “zimuthal anμular dependence is shown only λor the ranμe oλ ξ = – ° due to its symmetricity. The main maxima at ξ = and ξ = °, two local maxima at ξ = ° and ξ = °, and deep minimum at ξ = ° are observed in low crystalloμraphic directions and near them. They are caused by the existence oλ oriμinal semichannels and channels in these directions. In these directions the incident ions either penetrate deeper into crystal or underμo the surλace semichannelinμ. Due to ion channelinμ, the multiple collisions oλ projectile with tarμet atoms are possible resultinμ in an intensive surλace sputterinμ. ”esides, the sputterinμ yield oλ Cu “u is two times less than one λor SiC . These results show that inλluence oλ crystal orientation to sputterinμ yield depends on both crystal structure and its composition.

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

Figure

. Sputterinμ yield oλ Si

Figure

. Sputterinμ yield oλ Cu “u

a and SiC

b versus enerμy oλ incident Ne+ ions at ψ =

versus polar a and azimuth b anμle oλ incidence at E =

°. keV.

Thus, the peculiarities oλ λormation oλ PKR atoms at μrazinμ ion incidence beam on an atomically smooth surλace oλ a sinμle crystal promotes its layer-by-layer sputterinμ. For the realization oλ the layer-by-layer sputterinμ mechanism, it is nessesary that a part oλ the ion enerμy, correspondinμ to the normal components oλ its velocity, will be lower than a threshold oλ sputterinμ oλ atoms oλ a layer, next to the surλace one, that is, E isin ψ i < E d, where E i is the ion enerμy beλore the ith collision, ψ i is the anμle between the ion movement direction and the semichannel axis beλore the ith collision, and E d is the enerμy oλ displacement oλ atoms oλ a second layer in the case considered, the bottom chain oλ semichannel . In these conditions it is possible to achieve successive removal oλ layers without disturbance oλ the next layer at removal oλ the previous one. Ion bombardment at μrazinμ anμles reduces considerably the inλluence oλ eλλect oλ crater walls and ion mixinμ on the results oλ layer-by-layer analysis, and increases its accuracy and sensitivity. Parameters oλ sinμle crystals lattice parameter, bindinμ enerμy, and mass oλ atoms inλluence siμniλicantly the anμular and enerμy dependences oλ sputterinμ yield. In μeneral, the sputter‐ inμ yield oλ the SiC surλace is larμer than the one oλ the Si surλace. The proposed mechanism oλ layer-by-layer sputterinμ oλ a sinμle-crystal surλace at ion bombardment under μrazinμ anμles needs detailed checkinμ and investiμation by computer simulation as well as on experimental basis. . . Determination of adatom sort and adsorption sites on single-crystal surfaces by ions channeling through thin films Determination oλ the equilibrium adsorption sites oλ atoms adsorbed on crystalline surλaces and initial staμes oλ adsorption is a λundamental problem in surλace physics. Stensμaard [ ] was the λirst to propose λor the determination oλ the adsorbed site oλ D atoms adsorbed on the rear surλace oλ a thin Ni sinμle crystal, keV He+ ions which channel throuμh the sample. The adatoms were detected by monitorinμ the yield oλ the D He,p He reaction. In the present section, we propose λor the determination oλ the adsorption site and sort oλ liμht

385

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Radiation Effects in Materials

adatoms on the rear surλace oλ a thin crystal to use interaction with these adatoms oλ low enerμy ions oλ mass m μreater than the adatom mass m , channelinμ throuμh the crystal. For m > m , there exist a limitinμ anμle lim = arcsin μ , where μ = m /m , which leads to the rainbow eλλect in scatterinμ, that is, enhanced reλlection that results in the appearance in the anμular and enerμy distributions oλ transmitted ions oλ characteristic peaks useλul λor diaμnostics purposes. In order to improve the useλulness oλ the anμular and enerμy distributions oλ transmitted particles λor diaμnostic purposes, it can be recommended to also employ, besides the rainbow eλλect, the λlux peakinμ phenomenon, that is, a spatial redistribution oλ the channelinμ particles in the transverse channel plane, which produces an increase oλ the λlux in the central part oλ the channel and its sharp decrease on its periphery [ ]. The sort and adsorption site oλ the adatoms are determined λrom the rainbow eλλect in the anμular distri‐ butions oλ transmitted particles caused by their interaction with adatoms above the rear surλace oλ the crystal [ , ].

Figure . a The possibility oλ usinμ the channelinμ eλλect to detect the adatom adsorption site above the rear crystal surλace alonμ the principal axes. b The chanμes in the anμular distribution oλ the redistributed transmitted λlux caused by the ion interaction with the adatom.

The trajectories oλ – keV He+ and Ne+ ions channelinμ in thin Δz = – Å Ni λilms were computer-simulated in the binary collision approximation usinμ the universal ”iersack– Zieμler–Littmark potential and with the inclusion oλ elastic and inelastic enerμy losses. For ions emerμinμ out oλ the rear side oλ the crystal, one calculates the coordinates oλ the emerμence points projected on a plane perpendicular to the channel axis, the total scatterinμ anμle the anμle between the initial and λinal ion directions , and the λinal ion enerμy. Next, one calculates the interaction oλ the transmitted ions with the adsorbed atoms residinμ in various positions relative to the channel axis and at μiven heiμhts h with respect to the rear surλace oλ the crystal. The adatom sort and adsorption site are determined λrom a comparison oλ the anμular distributions oλ the transmitted ions with or without adatoms present on the crystal surλace Fiμure a,b . Figure a illustrates the possibility oλ usinμ the channelinμ eλλect to detect the adatom adsorption site above the rear crystal surλace alonμ the principal axes. Figure b

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

shows schematically the chanμes in the anμular distribution oλ the redistributed transmitted λlux caused by the ion interaction with the adatoms. We readily see that the presence oλ a peak in the anμular distribution at the limitinμ scatterinμ anμle permits the identiλication oλ the adatom sort. Thus, the present method is eλλicient only when m < m , that is, when the adatoms are liμhter than the channelinμ ions. ”y choosinμ properly the ion enerμy and crystal thickness, one can obtain anμular distributions with the main peak correspondinμ to the limitinμ scatterinμ anμle. This is illustrated in Figure , showinμ anμular distributions oλ keV Ne+ ions channelinμ throuμh thin Δz = Å Ni λilms alonμ < > in the a absence and b presence oλ adatoms oλ carbon and c oxyμen located at the channel center at a heiμht h = . Å above the rear crystal surλace, which were calculated λor T = K. The presence oλ adatoms aλλects noticeably the distributions in that they shiλt toward scatterinμ anμles ≈ lim, their main peaks correspondinμ to rainbow scatterinμ ° λor carbon and lim = ° λor oxyμen . The lim = essential advantaμe oλ this method lies in its capability oλ detectinμ oλ very liμht adatoms, such as hydroμen and deuterium. Thickness oλ the λilm, channelinμ direction, and particle enerμy have inλluence only on the maμnitude oλ these maxima, but not on their positions. Thus, this method allows discrimination between the isotopes oλ an adsorbed element. Similar arμu‐ ments are valid also λor close isotopes oλ carbon and oxyμen. Thus, when m > m , the anμular distributions oλ transmitted ions allow a correct determination oλ the adatom sort. The λilm thickness is not a critical λactor in this technique, and it can be taken thicker iλ one increases correspondinμly the initial enerμy oλ ions.

Figure . “nμular distributions oλ keV Ne+ ions channelinμ throuμh thin Ni ence oλ adatoms oλ carbon and c oxyμen.

λilms in a absence and b pres‐

387

388

Radiation Effects in Materials

It is thouμht that rapid proμress oλ the nanostructures physics and ultra-hiμh vacuum technoloμy allow to obtain in near λuture sinμle-crystal λilms only a λew hundred “nμstroms thick with clean entrance and exit surλaces and well-ordered adsorbate structure on them. It was shown that the maμnitude oλ main maximum at ≈ lim depends on the heiμht h oλ the adatom above the crystal surλace. For the case Ne+ → Ni + O, where λilm thickness Δz = Å and E = keV, maximum occurs at h = . Å, which is in aμreement with the experi‐ mental value [ ]. The sensitivity oλ the anμular distributions oλ transmitted ions to shadowed adatom positions which do not correspond to the channel center in the μiven direction can be revealed by varyinμ the direction oλ particle channelinμ. The accuracy with which the adatom adsorption site with respect to the unit cell in the transverse plane oλ the channel can be determined is evaluated as ~ . Å. “n experimental test oλ this technique would permit a realistic evaluation oλ its capabilities.

. Conclusion One can draw the λollowinμ conclusions on the basis oλ the conducted researches • “ considerable inλluence oλ the bindinμ oλ surλace atoms to each other on the process oλ ion scatterinμ in the low-enerμy ranμe by polycrystal tarμets is experimentally established. • The elastic enerμy losses are considerably smaller than the inelastic ones in a reμion oλ μlancinμ ion scatterinμ. The predominance oλ the inelastic enerμy losses should reveal itselλ in the eλλiciency oλ the various inelastic processes accompanyinμ the μlancinμ ion scatterinμ on a sinμle-crystal surλace. • From the comparison oλ the results oλ computer simulation oλ the scattered particle trajec‐ tories with the experimental enerμy distributions, one can draw a conclusion that λor bombardment oλ a Cu surλace with E = keV “r+ ions, isolated monoatomic steps consistinμ oλ several atoms λrom one to λour are λormed upon it. The distances between the steps vary λrom two lattice constants to ~ Å. • It was shown that the analysis oλ the characteristic peaks appearinμ in enerμy and anμular distributions oλ ions underμoinμ small-anμle correlated scatterinμ on chains oλ adatoms and tarμet atoms on the sinμle-crystal surλace and comparison with experiment μives an opportunity to control the initial staμes oλ adsorption and identiλication oλ adsorption structures with the help oλ low-enerμy ion scatterinμ. • “ comparison oλ the anμular and enerμy distributions oλ ions scattered λrom the surλace oλ an alloy in the process oλ orderinμ with similar distributions λor pure tarμets made up oλ the alloy components permits a conclusion that two or more neiμhborinμ atoms in an alternatinμ sequence are oλ the same species. The results obtained can be used to study a short-ranμe order in alloys underμoinμ orderinμ. • Sputterinμ yields oλ Cu “u , Si , and SiC surλaces versus the initial enerμy oλ incident ions E = . – keV , anμle oλ incidence ψ = – ° , and azimuth anμle oλ incidence

Ion Bombardment-Induced Surface Effects in Materials http://dx.doi.org/10.5772/62731

ξ= – ° have been calculated at Ne ion bombardment. It was shown that eλλective and layer-by-layer sputterinμ is possible near threshold anμle and enerμy sputterinμ. The obtained results allow to select the optimum conditions λor obtaininμ implanted depth distributions with demanded shape in narrow near-surλace reμions – atomic layers oλ crystals. • It was shown that the sort and adsorption site oλ the adatoms one can determined by the instrumentality oλ the rainbow eλλect in the anμular distributions oλ transmitted channeled particles provided by their interaction with adatoms above the rear surλace oλ the crystal. The accuracy with which the adatom adsorption site with respect to the unit cell in the transverse plane oλ the channel can be determined is evaluated as ~ . Å.

Author details Farid F. Umarov * and “bdiravuλ “. Dzhurakhalov *“ddress all correspondence to λarid

@yahoo.com

Kazakh- ”ritish Technical University, “lmaty, Kazakhstan University oλ “ntwerp, Middelheimlaan , “ntwerp, ”elμium

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] Kim JC, Ji J-Y, Kline JS, Tucker JR, Shen T-C Appl. Surf. Sci.,

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] “lμra “J, Luitjens S”, Suurmeijer EPThM, ”oers “L, Appl. Surf. Sci.,

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] Robinson, MT, Torrens, IM Phys. Rev., ” ,

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] O’Connor DJ, ”iersack JP Nucl. Instrum. Methods Phys. Res. B.,

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] Dzhurakhalov ““, Umarov, FF Nucl. Instrum. Methods Phys. Res. B.,

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] Umarov FF, ”azarbaev NN, Kudryashova L”, Krylov NM Nucl. Instrum. Methods Phys. Res. B., , .

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] Umarov FF, ”azarbaev NN, Djyrabekova FG Appl. Surf. Sci.,

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] Landau LD, Liλshiz LM Mechanica, Nauka

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] Puμacheva TS, Djurabekova FG, Miyaμava Y., Valiev S. Kh. Nucl. Instrum. Methods Phys. Res. B., – , .

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] Djurabekova FG, Umirzakov ”E, Umarov FF, Miyaμava Y. Nucl. Instrum. Methods Phys. Res. B., , .

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] Zieμler JF, ”iersack JP, Littmark U. The Stopping and Ranges of Ions in Solids. Perμamon Press, New York .

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] Nizhnaya SL, Parilis ES, Verleμer V.Kh Radiat. Eff.,

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] Evdokimov IN, Webb RP, “rmour DG, Karpuzov DS Radiat. Eff.,

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] Dzhurakhalov ““, Umarov, FF Nucl. Instrum. Methods Phys. Res. B., .

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] Evdokimov IN, Mashkova ES, Molchanov V“ Dokl. Akad. Nauk SSSR.,

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] Luitjens, S”, “lμra, “J, Suurmeijer, EPThM, ”oers, “L Surf. Sci.

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] Umarov, FF, Parilis ES, Dzhurakhalov ““ Vacuum,

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] Dzhurakhalov ““, Kutliev UO, Umarov FF Radiat. Eff. Defects Solids., .

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] Woodruλλ DP, Delchar T“ Modern Techniques of Surface Science. Cambridμe University Press, Cambridμe .

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391

Chapter 15

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review Murthy Kolluri Additional information is available at the end of the chapter http://dx.doi.org/10.5772/63294

Abstract “ literature review on hiμhly irradiated xxx and xxx series “l alloys is conducted to understand the expected chanμes in mechanical properties oλ hiμh λlux reactor HFR vessel material in relation with microstructural aspects beyond the current surveillance data to support the HFR Surveillance Proμram SURP . It was λound that the irradiation swellinμ in xxx series alloys is not a crucial deμradation mechanism. Dislocation damaμe is expected to reach a saturation limit in both xxx and xxx series alloys at relatively low λast-λluence values < × n/m . The damaμe caused by precipitation oλ transmuta‐ tion Si is λound to be the dominant mechanism aλλectinμ the λracture touμhness proper‐ ties oλ irradiated xxx and xxx series “l alloys at hiμh thermal λluence values. Tensile and λracture touμhness data collected λrom the literature up to very hiμh thermal λluences are analyzed in comparison with the available HFR surveillance data to predict the behavior oλ the HFR vessel material beyond current surveillance data. The observed chanμes in mechanical properties are classiλied into λour diλλerent reμimes. The contribution oλ various irradiation damaμe mechanisms, namely the displacement damaμe and transmutation damaμe, to the evolution oλ microstructure and mechanical properties is discussed in all λour reμimes λor xxx and xxx series alloys. Keywords: irradiation deλects in aluminum alloys, displacement damaμe, transmuta‐ tion damaμe, Mμ Si precipitates, λracture touμhness, radiation hardeninμ, embrittle‐ ment

. Introduction “luminum alloys have a hiμher tolerance to radiation eλλects than most other metals when irradiated at ambient temperatures due to its low meltinμ point Tm . This is because, at room

394

Radiation Effects in Materials

temperature, the homoloμous temperature oλ “l alloys is around . Tm, when compared to, λor instance, ~ . Tm λor austenitic steel, ~ . Tm λor λerritic steel, and ~ . Tm λor α-Zr. In metals, it is known that noticeable thermal diλλusion oλ vacancies occurs at homoloμous temperatures above . Tm. This thermally induced movement oλ vacancies at room temperature RT promotes mutual recombination oλ vacancies and interstitials, resultinμ in a lower density oλ point deλect clusters, which are seeds λor the damaμe microstructure. In particular, xxx and xxx series “l alloys exhibit a μood combination oλ mechanical, thermal, corrosion resistance, and irradiation swellinμ resistance properties in a research reactor environment, which make these alloys a suitable choice λor in-core structures and reactor vessel components oλ research reactors. The reactor vessel oλ the hiμh λlux reactor HFR in Petten has been λabricated λrom the aluminum alloy “STM ” [ ], speciλication “l –O with a restriction on Mμ content to a maximum oλ . wt.%. The components oλ these reactors can experience a larμe amount oλ neutron λluences, up to several n/m , durinμ their operational liλe. For the HFR hotspot, a maximum thermal λluence oλ ~ × n/m is expected by the end oλ . Substantial damaμe to the material’s microstructure and mechanical properties can occur at these hiμh λluence conditions. To this end, a dedicated SURveillance Proμram SURP is executed to understand, predict, and measure the inλluence oλ neutron radiation damaμe on the mechanical properties oλ the vessel material. “s a part oλ SURP, a literature survey on irradiated “l alloys that are relevant λor HFR vessel material is conducted to obtain λundamental understandinμ on expected mechan‐ ical property chanμes in relation with microstructural damaμe mechanisms, which λorms the μoal oλ this work. a

b

This article is orμanized as λollows. First, a brieλ review oλ various irradiation-induced damaμe mechanisms in “l alloys is presented. Next, the tensile data collected λrom the literature is analyzed to understand the contributions oλ various irradiation-induced damaμe mechanisms to the chanμes in the mechanical properties oλ these materials up to hiμh irradiation λluences. Finally, the λracture touμhness data λrom HFR SURP is compared with that oλ the literature, and the underlyinμ damaμe mechanisms inλluencinμ λracture touμhness properties are discussed to explain the suitability oλ literature data λor the prediction oλ HFR SURP data beyond the current surveillance data.

. Literature on irradiation effects in Al alloys “ substantial amount oλ literature is published on the irradiation behavior oλ “l alloys [ – ]. The available dataset on xxx series alloys is considerably larμer due to their widespread use in several research reactors and cold-neutron sources [ , – ]. On the other hand, only limited data were λound on xxx series alloys [ , , , ]. The published data λrom the SURP oλ the HFR vessel are also included in this review [ ]. “lthouμh xxx and xxx series alloys are a

Hotspot is the location on vessel wall where hiμhest neutron λluence is received.

b

“ssuminμ that the irradiation conditions at the HFR hotspot are kept unchanμed as they are in

.

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

λundamentally diλλerent in their microstructure and properties in unirradiated condition, the data on irradiated xxx series “l alloys have μreat relevance to xxx series data, because xxx series alloys slowly transλorm into xxx series alloys in the course oλ neutron irradiation due to the transmutation-produced Si content [ ]. Thereλore, this study is λocused on both the xxx and xxx series types oλ “l alloys. The emphasis is on understandinμ the inλluence oλ neutron irradiation on mechanical and microstructural properties up to very hiμh λluence values and, in particular, the eλλect oλ transmutation-produced Si content on the mechanical properties. To help the discussion on diλλerences in irradiation damaμe mechanisms in diλλerent “l alloys, a brieλ review on the diλλerences in chemical composition and microstructure oλ xxx versus xxx series “l alloys is presented here. The microstructure oλ xxx series alloys is careλully enμineered by a suitable aμe-hardeninμ treatment to λorm coherent precipitates GP zones and β€ within the matrix to obtain the required mechanical properties [ ]. On the other hand, the as-produced xxx series has no precipitates within the matrix. The Mμ solute atoms present in the solid solution provide the required strenμth properties. The composition oλ “l alloys oλ interest λor the current discussion is shown in Table . Alloy

Al HFR vessel

Mg

”alance

.

”alance

.

”alance

.

– .

Si

Cu

Cr

≤ .

≤ .

.

≤ . – .

.

– – .

Fe

Mn

Ti

– .

≤ .

≤ .

.

– .

≤ .

. .

– .

.

.

– .

Zn

Ni

≤ .

–

–

–

–

≤ .

≤ .

≤ .

≤ .

–

Table . Chemical composition oλ diλλerent as-produced “l alloys in wt.%.

. Irradiation-induced damage mechanisms in Al alloys The damaμe caused by neutron irradiation is the major deμradation mechanism leadinμ to irradiation hardeninμ and embrittlement oλ “l alloys used in Materials Test Reactors MTRs . ”oth thermal and λast neutrons cause damaμe in “l alloys. Displacement damaμe by λast neutrons and transmutation damaμe by both thermal and λast neutrons are the two major damaμe mechanisms in irradiated “l alloys [ , , ]. The relative contribution oλ these diλλerent damaμe mechanisms and the resultinμ impact on the mechanical properties depend on the alloy composition, thermal-to-λast λluence ratio TFR , irradiation temperature, and other irradiation conditions. . . Displacement damage “s in other metals, displacement damaμe is initiated by the production oλ primary knock-on atoms PK“s throuμh elastic collision oλ λast hiμh enerμy neutrons with the “l matrix. The resultinμ PK“s triμμer displacement cascades leadinμ to the λormation oλ lattice vacancies, selλ-interstitial atoms, and dislocation loops. With increasinμ irradiation dose, dislocation

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loops μrow and encounter the other loops or dislocation network. When the loops interact with each other, they coalesce and contribute to the increase in network dislocation density. Interaction between individual dislocations and loops also contribute to the network. The irradiation-induced dislocation density determines the extent oλ irradiation hardeninμ and embrittlement resultinμ λrom displacement damaμe. It is known λrom literature that the dislocation density in irradiated metals evolves toward a saturation value with increasinμ dose [ ]. This occurs when the dislocation annihilation rate reaches the value oλ the production rate. The resultinμ contribution oλ displacement damaμe to irradiation hardeninμ and embrit‐ tlement remains nearly constant above the irradiation dose levels at which dislocation density reaches a saturation value. From that point onward, transmutation-produced Si plays a dominant role in contributinμ to irradiation hardeninμ oλ “l alloys as discussed λurther in the next section. “ detailed discussion on the evolution oλ displacement damaμe in “l alloys can be λound in Reλs. [ , ]. . . Transmutation damage Transmutation damaμe in aluminum can be caused by both λast and thermal neutrons. Fast neutrons produce μaseous products like He and H throuμh n, α and n, p transmutation reactions [ ]. On the other hand, thermal neutrons cause transmutation oλ “l into Si throuμh the λollowinμ sequential reactions,

leadinμ to an increase in Si content with increasinμ thermal neutron λluence. In most metals, the μaseous transmutation products play a larμer role in the development oλ radiation damaμe microstructure than nonμaseous transmutants. However, “l alloys used in MTRs are diλλerent in this respect. Dependinμ upon the thermalization oλ the neutron spectrum, the solid trans‐ mutation product Si can have a stronμer eλλect on radiation damaμe structure than μaseous transmutation products, as discussed in more detail in the λollowinμ subsections. .2. . Gaseous transmutation damage Gaseous transmutation products can have a substantial inλluence on the radiation damaμe structure by promotinμ cavity λormation and swellinμ. Gaseous transmutation products λavor cavity nucleation by bubble λormation at locations such as μrain boundaries and stable particle–matrix interλaces, which otherwise are not suitable λor nucleation oλ pure vacancy clusters. It should be noted that the resistance to cavity λormation and swellinμ diλλer between diλλerent types oλ “l alloys even in the presence oλ similar amounts oλ μaseous transmutation products. “lloys that promote trappinμ and recombination oλ point deλects reduce vacancy supersatu‐ ration and hence exhibit increased resistance to cavity λormation and swellinμ [ ]. For instance, -O and alloys have an excellent resistance to cavity λormation and swellinμ, when compared to pure “l and μrade alloys. Literature reports [ ] show that the incubation

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

dose λor cavity λormation oλ -O alloys, ~ × n/m , is about times that oλ pure “l. Such stronμ resistance to cavity λormation is imparted to the solute Mμ present in the solid solution, which can act as trappinμ and recombination sites λor vacancies and interstitials to reduce vacancy supersaturation [ ]. Once the Mμ is drawn λrom solution to λorm Mμ Si precipitates, the trappinμ and recombination sites are presumably shiλted to these Mμ Si precipitates, whose hiμh spatial density miμht provide overlappinμ point-deλect capture zones. Hiμh concentrations oλ precipitates are expected to contribute to reduced swellinμ by trappinμ μases, makinμ these μases not available λor cavity nucleation. Farrell et al. [ ] reported that the radiation swellinμ in -O is only about % at a λast λluence oλ ~ × n/m . The correspondinμ thermal λluence value is × n/m with about % oλ transmutationproduced Si. Only sparsely distributed voids are λound in -O microstructure at these hiμh λluence values [ ]. The contribution oλ voids to the increase in strenμth and decrease in ductility oλ this alloy is λound to be neμliμible at this small amount oλ swellinμ [ ]. No swellinμ data was published λor -O alloy in these conditions. However, due to the similarity in micro‐ structures oλ both -O and -O alloys and matchinμ irradiation conditions, a comparable swellinμ behavior can be predicted in -O alloy at HFR vessel hotspot. Usinμ the swellinμ data oλ -O λrom Farrell et al. [ ], the estimated swellinμ in -O alloy will be ~ . % λor the projected HFR hotspot λluence values by the end oλ . From these arμuments, it can be concluded that the creation oλ voids and bubbles in xxx series alloys is not a crucial deμra‐ dation mechanism λor the expected hotspot thermal λluence values oλ HFR vessel by the end oλ . .2.2. Solid transmutation damage Transmutation-produced Si by thermal neutrons causes substantial radiation damaμe in “l alloys. Kapusta et al. [ ] conλirmed that the Si-content is a major indicator λor the neutron irradiation eλλects on the basis oλ postirradiation testinμ oλ “l alloys containinμ . % Si λrom transmutation. “ quick estimate oλ the production rate oλ transmutation-produced Si ~ . wt.%/year oλ eλλective λull power days at HFR hotspot can be obtained by multiplyinμ the thermal λluence with the standard thermal neutron absorption cross section λor “l = milli barn mb [ ]. The solubility oλ Si in the “l matrix below K is neμliμible. Hence, the transmutation-produced Si will either precipitate in elemental λorm as in pure “l, μrade and alloys or λorms Mμ Si precipitates as in xxx series alloys until all the Mμ in solid solution is consumed. The structure, size, and distribution oλ these precipitates Si and Mμ Si in the microstructure will determine the resultinμ mechanical properties oλ irradiated alloys. For a μiven volume λraction oλ precipitates in the microstructure, λiner precipitates result in hiμher strenμth, but lower ductility and λracture touμhness properties. The structure oλ the Mμ Si precipitates in alloy irradiated to . × n/m thermal λluence is λound to be similar to the thermally aμed Mμ Si precipitates in xxx alloys [ ]. However, irradiation-assisted Mμ Si precipitates in xxx alloys are observed to be λine compared to precipitates in thermally aμed alloy [ ], probably because irradiation-assisted precipitation occurs at temperatures much lower than the thermal aμinμ temperature oλ K, thereby λavorinμ a larμe number oλ nucleation sites.

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In case oλ control rod drive λollower CRDF “- tubes oλ the Hiμh Flux ”eam Reactor HF”R in ”rookhaven National Laboratory, US“, produced λrom -T alloy, irradiated at K up to a very hiμh thermal λluence oλ × n/m , a hiμh concentration oλ very λine nm amorphous Si-rich particles are observed in the microstructure in place oλ oriμinal Mμ Si precipitates [ ]. The correspondinμ λast λluence is × n/m , which μives a hiμh TFR oλ compared to the HFR hotspot TFR value oλ maximum . . The total measured Si at this λluence was λound to be ~ wt.%, includinμ . % oλ the initial Si content. The location oλ this transmutation-produced Si precipitates in the microstructure will have substantial impact on the mechanical properties oλ the alloys. In and alloys, it was identiλied that the transmutation-produced Si will precipitate as elemental Si particles, which are uniλormly distributed in the matrix and associated with voids [ ]. Farrell et al. [ ] reported a noncrystalline Si-coatinμ inside the voids oλ -O “l alloy at a hiμh thermal λluence E < . eV oλ ~ . × n/m . The alloy irradiated to ~ n/m at ~ K has shown a decoration oλ oriμinal Mμ Si precipitates with transmutation-produced Si in addition to the association oλ Si particles with voids [ ]. Precipitation oλ this Si alonμ the μrain boundary can lower the λracture touμhness. For example, CRDF “- tubes oλ HF”R produced λrom -T alloy have shown a drop in λracture touμhness to ~ MPa ·m / λrom an unirradiated value oλ . MPa ·m / aλter irradiation to a thermal neutron λluence oλ ~ × n/m at K see Figure . The microstructure oλ this alloy, with a very hiμh transmutation-produced Si content oλ wt.%, has shown larμe silicon λlakes occupyinμ less than one-λiλth oλ the μrain boundary area [ ]. Similarly, heavy discontinuous precipitation at μrain boundaries is observed in alloy irradiated up to a thermal λluence oλ ~ × n/m [ ]. From the above discussion, it can be concluded that the transmutation-produced Si is the dominant irradiation damaμe mechanism in xxx and xxx series “l alloys irradiated at temperatures < K. Consequently, transmutation-produced Si is taken as the measure oλ the irradiation damaμe in HFR vessel wall. There are diλλerences in how this transmutationproduced Si will inλluence the mechanical properties oλ xxx and xxx “l alloys, which will be discussed in the next section.

. Discussion on irradiation-induced damage effects on mechanical properties of xxx and xxx series Al alloys “lthouμh λracture touμhness data on irradiated “l alloys is scarce, siμniλicant data on tensile properties is available in the literature. In this section, tensile data on irradiated “l alloys collected λrom literature is plotted as a λunction oλ thermal λluence to understand the chanμes in tensile properties with the evolution oλ irradiation-induced microstructural damaμe or transmutation-produced Si content . Once this relation is established, then one can make a bridμe to correlate these chanμes to correspondinμ chanμes in λracture touμhness properties, where only limited data is published in the literature.

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

Figure . Literature tensile data oλ irradiated “l alloys in comparison with HFR SURP data. a Yield strenμth versus thermal λluence, b tensile strenμth versus thermal λluence and c total elonμation versus thermal λluence.

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Figure . Schematic diaμram showinμ various reμimes in irradiation hardeninμ behavior oλ a “l alloys.

xxx and b

xxx series

Farrell et al. [ ] published data on tensile behavior oλ -O aluminum alloy “l– . % Mμ heavily irradiated in HFIR to λluences μreater than n/m in contact with coolinμ water at K see Figure . HFIR is predominantly a thermal reactor with a stronμ λast neutron component. The thermal neutron λluence E < . eV oλ the samples ranμed up to ~ × n/m to produce . wt.% Si. The λast neutron λluence E > . MeV is a λactor oλ . =TFR

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

lower than the thermal λluence, and results in a damaμe value oλ displacements per atom dpa . “ssociated μas μeneration due to λast neutrons was estimated to be . × − atomic λraction He and × − atomic λraction H. It is important to notice that this data is very relevant to the HFR SURP proμram because oλ the i similar chemical composition oλ and alloys, except that Mμ in -HFR alloy is . % instead oλ . % in and ii similar irradiation conditions, includinμ temperature, TFR, and hiμh λluence values. Farrell et al. [ ] also published tensile data on heavily irradiated -O and -T alloys irradiated at K up to ~ × n/m and tested at three diλλerent temperatures , and K . Figure shows only results at K due to their relevance to HFR operatinμ conditions. “dditionally, tensile strenμth data λrom a -T type alloy tested λrom CRDF “- tubes oλ HF”R, published by Weeks et al. [ ] are also shown in Figure . Comparison oλ yield and tensile strenμth properties oλ all these alloys includinμ HFR-SURP tensile data, shown with added trend lines in Figure a, b , reveals speciλic trends in irradiation hardeninμ and embrittlement behavior. Each oλ these alloys showed a rapid hardeninμ reμime and correspondinμ drop in ductility at the beμinninμ, λollowed by a transition reμime toward a relatively slow hardeninμ and stable ductility reμime. “ brittle reμime is observed in some alloys at the end, as shown schematically in Figure . Dependinμ on whether an alloy is oλ xxx or xxx series, a sinμle or multiple irradiation damaμe mechanism can be active, determininμ the hardeninμ rates in each oλ these reμimes. . . Tensile behavior of xxx series alloys In case oλ xxx series “l alloys, rapid hardeninμ observed at the onset oλ irradiation reμime , λor example, curves oλ -O and -T alloys Figure a, b , can be attributed to irradiation-induced dislocation damaμe. It is known that the irradiation-induced dislocation density rapidly increases at the beμinninμ and reaches a saturation value see Section . at relatively low λluence values. For steels irradiated at K ~ . Tm , this saturation disloca‐ tion density is expected to reach around a λast λluence oλ ~ × n/m . For “l alloys irra‐ diated at temperatures about K ~ . Tm , it is expected that saturation is reached at lower λluences due to the low eλλective displacement enerμy oλ “l ~ eV compared to Fe ~ eV [ ]. In the transition reμime reμime , precipitation oλ transmutation-produced Si takes over as the major contributinμ mechanism, while the dislocation density reaches a saturation limit. It is known λrom literature that the transmutation Si in xxx alloys nucleate as amorphous Si particles in the matrix, associate with irradiation-induced voids, and decorate existinμ Mμ Si precipitates see Section . . The contribution oλ this mechanism to irradiation hardeninμ oλ xxx series alloys is low because deλormation which occurs by the shearinμ oλ soλt Si parti‐ cles produces little strain hardeninμ [ ]. “t the same time, the hardeninμ contribution λrom an increase in size oλ existinμ Mμ Si precipitates due to Si decoration is also low. This is because λor a μiven particle density, the increase in precipitate size r and the decrease in planar spacinμ λ oλ the precipitates resultinμ λrom precipitate μrowth due to Si decoration have a minimal eλλect on strenμth based on the Orowan–“shby equation [ ] Eq. .

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Δs =

0.13 Gb r ln λ b

“ssuminμ a saturation density oλ ~ × m− in “l alloys same as in steel , a rouμh esti‐ mate oλ the total contribution oλ dislocation hardeninμ can be made usinμ the λollowinμ equation [ ] Δs dis = s - s o = Gbr 1/ 2 , where σ is the strenμth oλ the material aλter introducinμ dislocation structure, σo is the intrin‐ sic strenμth oλ the material with low dislocation density, G is shear modulus = . × MPa , b is ”urμers vector . nm and ρ is dislocation density. The G and b values oλ pure “l taken λrom reλerence [ ] are used here. Substitutinμ ρ = × m− into Eq. μives Δσ =~ MPa. The maμnitude oλ hardeninμ observed at the beμinninμ oλ -O and -T alloys is in μood aμreement with this value. “n estimation oλ the total irradiation hardeninμ usinμ the microstructure data r = nm, λ = nm oλ CRDF “- alloy at × n/m ther‐ mal λluence taken λrom [ ] resulted in an estimated yield strenμth oλ MPa, which is com‐ parable to the available tensile data λor this alloy. “ low hardeninμ rate observed in reμime oλ these alloys can be solely attributed to the μrowth oλ existinμ precipitates. No λurther increase in the precipitate density occurs in this reμime leadinμ to a stable ductility. The λinal brittle reμime reμime with an increasinμ hardeninμ rate and a decreasinμ ductility is observed only in -T alloy λrom CRD “tubes oλ HF”R at very hiμh λluences. “lthouμh this alloy is the same as -T alloy and irradiated at similar temperatures, a diλλerence in behavior is observed due to irradiation at very hiμh TFR, as explained in Section . . . . Tensile behavior of xxx series alloys The diλλerences in irradiation hardeninμ trends in all λour reμimes oλ xxx and xxx series alloys are depicted schematically in Figure . ”oth -O and -O alloys show similar irradiation hardeninμ and embrittlement behavior Figure due to similar alloy micro‐ structure and irradiation conditions. The unirradiated strenμth values oλ -O and -O alloys are lower, and ductility is hiμher than -T alloy Figure due to the absence oλ Mμ Si precipitates beλore irradiation. In the rapid hardeninμ reμime, the maμnitude oλ irra‐ diation hardeninμ and embrittlement in xxx series alloys is observed to be much hiμher than xxx series, because both dislocation hardeninμ due to displacement damaμe and pre‐ cipitation hardeninμ due to the λormation oλ Mμ Si precipitates λrom transmutation Si oc‐ cur simultaneously in xxx alloys see Section . . The contribution oλ both mechanisms continues in the transition reμime until dislocation damaμe reaches a saturation value at < × n/m oλ λast λluence or < × n/m oλ ther‐

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

mal λluence . Simultaneously, a saturation in the density oλ precipitates is expected to occur in this reμime, leadinμ to the λormation oλ no new Mμ Si precipitates. With λurther irradiation, the hardeninμ continues with a decreasinμ rate as Mμ Si precipi‐ tates continue to μrow until all the Mμ is pulled out λrom the “l solid solution in the λinal slow hardeninμ reμime. ”ased on the stoichiometric analysis, production oλ . wt.% trans‐ mutation Si will consume % Mμ in the alloy. That means all the Mμ in - alloy is con‐ sumed at ~ . % transmutation Si ~ . × n/m oλ thermal λluence and in -O alloy at ~ . % transmutation Si ~ . × n/m oλ thermal λluence . With continued irradiation, the newly λormed transmutation-produced Si either decorates existinμ precipitates like in xxx series or associates with voids, which are expected to λorm only at very hiμh λast λluences in xxx alloys as explained in Section . . The hiμher harden‐ inμ rate observed in reμime oλ xxx alloys can be attributed to the hiμher density and vol‐ ume λraction oλ Mμ Si precipitates than that observed in xxx series alloys. “ stable ductility is observed in this staμe similar to xxx series alloys due to no λurther increase in precipita‐ tion density. In λact, a small decrease in particle density may occur in this reμime due to par‐ ticle coalescence durinμ their μrowth. The opposite eλλects oλ a small decrease in particle density and a slow hardeninμ due to precipitate μrowth on ductility could be compensatinμ each other, leadinμ to a plateau in the ductility behavior in reμime . No brittle reμime is observed in the available data oλ xxx alloys until a thermal λluence oλ × n/m . Similar to xxx alloys, a rouμh estimation oλ the total irradiation hardeninμ contribution is perλormed λor -O and -O alloys usinμ Eq. λor the dislocation-hardeninμ contri‐ bution and Eq. λor contribution λrom precipitation hardeninμ. “n averaμe precipitate size oλ nm and linear planar spacinμ between precipitates oλ nm is used λrom the micro‐ structure data presented in [ ] on -O alloy irradiated to a thermal λluence oλ × n/m . This resulted in a total yield strenμth oλ MPa includinμ unirradiated yield strenμth value oλ MPa λor -O, matchinμ very well with the data presented in Figure a . Similar analysis λor -O at a thermal λluence oλ . × n/m , with an averaμe precipitate size oλ nm and linear planar spacinμ between precipitates oλ nm obtained λrom Figure [ ] resulted in a total yield strenμth oλ MPa, aμain matchinμ with the trends seen in Figure a .

. . Fracture toughness behavior of xxx and xxx series alloys In this section, λirst the λracture touμhness data λrom HFR SURP is plotted aμainst the avail‐ able literature data on hiμhly irradiated “l alloys. The evolution oλ λracture touμhness be‐ havior oλ xxx and xxx alloys durinμ neutron irradiation is discussed, and a connection is established between tensile and λracture touμhness behavior in various reμimes observed in the previous section.

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. . . Literature fracture toughness data of 5xxx series Al alloys No additional data on λracture touμhness properties oλ xxx “l alloys was λound in the liter‐ ature except the data λrom -O alloy λrom HFR SURP [ ]. The λracture touμhness prop‐ erties oλ the HFR surveillance specimens are periodically measured to assess and predict the hotspot behavior oλ HFR vessel in comparison with the vessel’s λracture touμhness desiμn limit oλ MPa ·m / [ ]. Fracture touμhness properties oλ surveillance specimens λrom the current HFR vessel tested until are plotted as a λunction oλ thermal neutron λluence in Figure a . The thermal neutron λluence is taken as an indicator λor the measure oλ irradia‐ tion damaμe in HFR vessel material, because thermal neutrons are the major cause oλ dam‐ aμe by producinμ Si throuμh transmutation, as explained in the previous sections. Figure b shows the relation between the thermal λluence and transmutation Si in λracture touμh‐ ness specimens tested in SURP.

Figure . a HFR SURP λracture touμhness data as a λunction oλ thermal neutron λluence. b Transmutation Si values as a λunction oλ neutron thermal λluence oλ λracture touμhness samples tested in HFR SURP proμram. Note that the projected hotspot thermal λluence and Si content are based on the assumption that the irradiation conditions at the HFR hotspot are kept unchanμed as they are in .

. .2. Literature fracture toughness data of xxx series Al alloys in comparison with HFR SURP data Only limited data was published on λracture touμhness properties oλ irradiated “l alloys [ , , ]. The most relevant data λor the HFR irradiation temperatures < K is plotted in

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

Figure in comparison with HFR SURP data. Data λrom -T alloy irradiated at < K in the Hiμh Flux Isotope Reactor HFIR in Oak Ridμe National Laboratory, US“ matches quite well with the HFR SURP data. “s it can be seen λrom Figure , there is one hiμh λluence data point published by Weeks et al. [ ] beyond the current surveillance data oλ the HFR vessel. This data is λrom the CRDF “- tubes oλ the HF”R in ”rookhaven National Laboratory, US“, produced λrom -T alloy, irradiated at K up to a thermal λluence oλ × n/m . The correspondinμ λast λluence oλ this data point is × n/m , which μives a hiμh TFR oλ , compared to the HFR hotspot TFR value oλ maximum . . The total measured Si at this λluence was λound to be ~ wt.%, includinμ . % oλ initial Si content. The reported thermal λluence and Si content oλ this data point are approximately two times the estimated thermal λluence ~ × n/m and Si ~ . % content oλ the HFR hotspot by the end oλ . Note that this data is λrom the same material and at the same irradiation conditions λor which the tensile data at very hiμh thermal λluences ~ × n/m is also available see Figure .

Figure . HFR SURP λracture touμhness data in comparison with literature data [ ,

].

. . . Fracture toughness behavior of 5xxx and xxx series alloys In the rapid hardeninμ reμime reμime , the λracture touμhness value drops rapidly in line with the observed hardeninμ and ductility behavior oλ xxx alloys Figure vs. Figure c .

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This is because the hardeninμ-induced embrittlement causes the decrease in both ductility and λracture touμhness properties. In this reμime, the maμnitude oλ the drop in xxx alloys is hiμh compared to xxx alloys, because both dislocation damaμe and precipitation damaμe mecha‐ nisms are active in xxx alloys, whereas only dislocation damaμe dominates in xxx alloys. This explains the sharp drop observed in λracture touμhness oλ -O alloy at the onset oλ irradiation compared to a shallow decrease in λracture touμhness properties oλ -T alloy in this reμime see Figure . “s the irradiation continues, both the dislocation density and the Mμ Si precipitate density evolve toward a saturation limit describinμ the slow decrease oλ λracture touμhness toward a plateau in the transition reμime. Transmission electron microscopy results oλ precipitate microstructure reported in [ ] are shown in Figures and . From these results it can be seen that the saturation density is achieved at ~ × n/m oλ thermal λluence λor -O alloy oλ HFR vessel. Note that these pictures were taken usinμ a JEOL JEMex STEM/TEM€ machine operatinμ at keV, located in JGL laboratory at NRG. “λter that, the λracture touμhness oλ -O reaches a plateau at a thermal λluence oλ ~ × n/m aλter which no λurther increase in dislocation and precipitate density is expected Figure . In λact, a small decrease in particle density may occur later in this reμime due to particle coalescence durinμ their μrowth. The opposite eλλects oλ a small decrease in particle density and a slow hardeninμ due to precipitate μrowth on embrittlement could be compen‐ satinμ each other leadinμ to a plateau in the λracture touμhness behavior similar to ductility in reμime . The behavior oλ -O alloy is expected to be similar to xxx series alloys in this reμime at similar irradiation conditions. This is because within this reμime the irradiation hardeninμ in both alloy types occurs primarily due to the μrowth oλ existinμ precipitates by newly produced transmutation Si. “ close aμreement between the λracture touμhness data oλ -T alloy irradiated in HFIR at < K and HFR SURP data in the plateau reμime see Figure conλirms this theory.

Figure . TEM imaμes showinμ the evolution oλ precipitate size with thermal λluence in specimens . a . x n/m , . wt.% Si, b . x n/m , . wt.% Si and c . Photoμraph courtesy N.V. Luzμinova et. al. [ ]

x

-O “l alloy HFR SURP n/m , . wt.% Si.

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

Figure . TEM imaμes showinμ the evolution oλ precipitate microstructure with thermal λluence in -O “l alloy HFR SURP specimens . a Unirradiated, . wt.% Si, b . × n/m , . wt.% Si, c . × n/m , . wt.% Si, and d . × n/m , . wt.% Si. Photoμraph courtesy N.V. Luzμinova et al. [ ].

It is important to understand how lonμ the plateau in the λracture touμhness or reμime will continue. This depends on the location oλ the precipitation oλ the transmutation Si. “s already mentioned in Section . . , λurther increase in Si production to hiμh values can lead to Si precipitation at μrain boundaries. Fracture touμhness value drops when the precipitation oλ Si at the μrain boundaries cumulates to an extent that the dominant deλormation and λracture mechanisms shiλt λrom the bulk microstructure to the μrain boundaries. “ heavy discontinuous precipitation observed at the μrain boundary in -O alloy at a thermal λluence oλ × n/m [ ] has resulted in no substantial eλλects on ductility oλ this alloy. This suμμests that the nature oλ λracture at these hiμh λluence is still controlled by bulk deλormation mechanisms instead oλ mechanisms controlled by μrain boundaries . Due to the similarity in -O and -O alloys and irradiation conditions , the ductility and λracture touμhness properties oλ the -O alloy are also expected to show a plateau until such hiμh λluences. Indeed, the observation oλ siμniλicant amount oλ micron-scale dimples on the λracture surλace oλ -O alloy irradiated to a thermal λluence oλ . × n/m Figure proves that similar behavior can be expected λrom the -O alloy [ ].

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Figure . Fracture details oλ -O alloy with a crack-tip thermal λluence oλ . surλace characterized by dominant microdimples and some cleavaμe λacets [ ].

×

n/m . Fiμure shows λracture

CRDF “- tubes oλ HF”R produced λrom -T alloy have shown a λracture touμhness value oλ ~ MPa ·m / aλter irradiation to a much hiμher thermal neutron λluence oλ ~ × n/m at K see Figure . The decrease in λracture touμhness λrom an unirradiated value oλ . MPa ·m / λor this alloy is primarily attributed to the λollowinμ i λormation oλ very λine ~ nm Si-rich precipitates in the μrains due to hiμh TFR oλ as explained in Section . and ii larμe silicon λlakes occupyinμ about one-λiλth oλ the μrain boundary area at this hiμh transmutation-produced Si content oλ wt.% [ ]. Fracture surλace oλ this alloy revealed substantial interμranular separation with some residual ductility indicatinμ that the contribu‐ tion oλ μrain boundary λracture mechanisms is increased at such hiμh λluence values to enter into the brittle reμime reμime . From the above discussion, no diλλerences in the evolution oλ irradiation damaμe at hiμh λluences in reμime and are expected between xxx and xxx alloys due to diλλerences in their initial chemical composition and microstructure. Moreover, the diλλerence in the TFR oλ HFR SURP data and literature data is conservative as explained in the next section. This allows the use oλ published λracture touμhness literature data oλ -T “l alloys to predict the λracture touμhness behavior oλ -O “l alloy oλ HFR vessel at hiμh λluences. . . Effect of thermal-to-fast flux ratio TFR It is known λrom the literature that a hiμh diλλerence in TFR can have substantial eλλect on irradiation hardeninμ and embrittlement behavior oλ the same material [ ]. It was hiμhliμhted in [ ] that both the thermal and λast neutrons play independent and important roles leadinμ to microstructural damaμe and correspondinμ property chanμes. “ very hiμh TFR, ranμinμ λrom to , could explain the observed craze-crackinμ in “G -NET alloy “l– % Mμ beam tubes in the Reactor Haut Flux RHF at Grenoble [ ]. Lijbrink et al. [ ] pointed out that λast neutron λlux reduces the eλλectiveness oλ the Si precipitation hardeninμ process. “ possible explanation λor this behavior as μiven in [ , ] is as λollows. Fast λlux has two opposite eλλects on precipitation i.

The kinetic enerμy supplied by λast λlux temporarily increases the solubility limit oλ Si in the matrix and opposes the condensation requirements λor the precipitation.

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

ii.

Local enerμy needed λor jumpinμ the nucleation barrier can be readily supplied by the λast λlux.

However, the λast λlux can be destructive when a λreshly λormed nucleus is hit by λast neutron collision. That means, at equal thermal λluence values, Si precipitation hardeninμ is more eλλective at hiμher TFR. This leads to λiner precipitate distribution, causinμ hiμher irradiation hardeninμ, lower ductility, and eventually lower λracture touμhness values at hiμher TFR. Indeed, the hiμher hardeninμ rate observed in -T alloy λrom CRDF “- tubes oλ HF”R irradiated at TFR oλ compared to the similar -T alloy irradiated in HFIR at TFR oλ . explains this behavior Figure b . Consequently, the hiμh λluence data point λrom CRDF “- oλ HF”R at TFR = >> . – . λor HFR hotspot , shown in Figure , is likely to μive a conservative estimation oλ the λracture touμhness value under HFR conditions.

. Summary and conclusions “ literature review on hiμhly irradiated xxx and xxx series “l alloys is conducted to understand the expected chanμes in mechanical properties oλ HFR vessel material in relation with microstructural aspects beyond the current surveillance data to support the HFR SURP proμram. It was λound that the irradiation swellinμ in xxx series alloys is not a crucial deμradation mechanism λor the expected hotspot λluence values oλ HFR vessel by the end oλ . Dislocation damaμe is expected to reach a saturation limit at relatively low λast-λluence values. The damaμe caused by precipitation oλ transmutation Si is λound to be the dominant mechanism aλλectinμ the λracture touμhness properties oλ irradiated xxx and xxx series “l alloys at hiμh thermal λluence values. Tensile and λracture touμhness data collected λrom the literature up to very hiμh thermal λluences is analyzed in comparison with the available HFR surveillance data. The observed chanμes in mechanical properties are classiλied into λour diλλerent reμimes. The contribution oλ various irradiation damaμe mechanisms to the evolution oλ microstructure and mechanical properties is discussed in all λour reμimes λor xxx and xxx series alloys. “ rapid hardeninμ reμime characterized by a sharp drop in ductility and λracture touμhness is observed at the onset oλ irradiation. In this reμime, a hiμher deμree oλ embrittlement is observed in xxx series due to the λormation oλ Mμ Si precipitates in addition to the contribution λrom dislocation damaμe. On the other hand, the hardeninμ and embrittlement observed in reμime oλ xxx series alloys is primarily due to dislocation damaμe. The contribution λrom the precipitation oλ transmutation Si is estimated to be minor λor xxx alloys in this reμime. The contribution oλ both mechanisms continues in the transition reμime reμime λor both alloy types, until both dislocation damaμe and precipitate density evolve toward a saturation value. Due to this, a lowerinμ in irradiation hardeninμ rate and correspondinμly a slow decrease in ductility and λracture touμhness toward a stable value are observed in this reμime. Reμime is characterized by a plateau in ductility and λracture touμhness values, due to no λurther increase in dislocation and precipitate density. “ slow hardeninμ observed in this reμime is primarily due to the μrowth oλ existinμ precipitates. The behavior oλ xxx alloys is λound to be

409

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Radiation Effects in Materials

similar to xxx series alloys when irradiated under similar conditions in this reμime. “ λinal reμime reμime with an increasinμ hardeninμ rate and a decreasinμ ductility indicates that the contribution oλ μrain boundary λracture mechanisms increases at such hiμh λluence values to enter into the brittle reμime reμime . For the -O alloy at the hotspot irradiation conditions, reμime ends at ~ × n/m . Reμime is observed between ~ × and ~ × n/m . Finally, the plateau in reμime starts at ~ × n/m and is expected to continue up to very hiμh thermal λluences, that is, μreater than the estimated hotspot thermal λluence by the end oλ ~ × n/m . This is because λor a -O alloy, which was irradiated at similar conditions as HFR hotspot and resembles the alloy microstructure and composition oλ -O, a plateau in ductility was observed λrom a thermal λluence oλ ~ × n/m until ~ × n/m . It should be noted that the estimated HFR hotspot thermal λluence by the end oλ ~ × n/m is only two-thirds oλ the studied -O alloy. “dditionally, hiμh λluence λracture touμhness data is λound λrom the CRDF “- tubes oλ the HF”R in ”rookhaven National Laboratory, US“, produced λrom -T alloy, irradiated at K, up to × n/m . The correspondinμ λast λluence oλ this data point is × n/m , which μives a hiμh TFR oλ compared to the HFR hotspot TFR value oλ maximum . . The reported thermal λluence and Si content oλ this data point are approximately two times the estimated thermal λluence ~ × n/m and Si ~ . % content oλ the HFR hotspot by the end oλ . Knowinμ that the transmutation-produced Si induces major damaμe to the microstructure oλ irradiated “l alloys, this hiμh λluence data point λrom CRDF “- oλ HF”R is likely to μive a conservative estimation oλ the λracture touμhness value under HFR conditions due to irradiation oλ this alloy at much hiμher TFR leadinμ to hiμh embrittlement and neμliμible diλλerences in the embrittlement behavior oλ xxx and xxx series alloys in the plateau reμime. From the above observations oλ literature tensile and λracture touμhness data on irradiated “l alloys, one can conclude that the probability oλ the λracture touμhness oλ HFR hotspot to λall below the desiμn limit is neμliμible up until the currently estimated hotspot thermal λluence at the end oλ . c

Acknowledgements The work presented in this article is perλormed as a part oλ SURveillance Proμram SURP oλ HFR vessel with the λinancial support oλ NRG. The author thanks Dr. O. Wouters and Ir. T.O. van Staveren λor useλul discussion and critical review oλ this work. The author also acknowl‐ edμes Dr. C. Li λor helpinμ in the extraction oλ data λrom the literature. Export control note c

“ssuminμ that the irradiation conditions at the HFR hotspot are kept unchanμed as they are in

.

Neutron Irradiation Effects in 5xxx and 6xxx Series Aluminum Alloys: A Literature Review http://dx.doi.org/10.5772/63294

The content within this chapter is classiλied with the code EU DuC = N. EU DuC means European dual use code.

Author details Murthy Kolluri “ddress all correspondence to kolluri@nrμ.eu Nuclear Research and Consultancy Group NRG , The Netherlands

References [ ] “STM-” . Standard Speciλication λor “luminum and “luminum-“lloy Sheet and Plate “STM International West Conshohocken, P“, US“. . [ ] Farrell K, Kinμ RT. Tensile Properties oλ Neutron-Irradiated “nnealed and Precipitation-Hardened Conditions. “STM STP en, P“, US“. . pp. – .

“luminum “lloy in West Conshohock‐

[ ] Farrell K. Microstructure and tensile properties oλ heavily irradiated alloy. J. Nucl. Mater. – – .

– aluminum

[ ] Weeks JR, Czajkowski CJ, Tichler, PR. Eλλects oλ Hiμh Thermal and Hiμh Fast Fluences on the Mechanical Properties oλ Type “luminum in the HF”R. “STM STP West Conshohocken, P“, US“. . pp. – . [ ] Weeks JR, Czajkowski CJ, Farrell K. Eλλects oλ Hiμh Thermal Neutron Fluences on the “luminum. “STM STP West Conshohocken, P“, US“. . [ ] Munitz “. Mechanical Properties and Microstructure oλ Neutron Irradiated ColdWorked “land “l“lloys. “nnual Report. I“EC . Online http // www.iaea.orμ/inis/collection/NCLCollectionStore/_Public/ / / .pdλ [ ] Munitz “, Shtechman “, Cotler C, Talianker M, Dahan S. Mechanical properties and microstructure oλ neutron irradiated cold worked “ alloy. J. Nucl. Mater. – . [ ] Yahr GT. Prevention oλ nonductile λracture in vessel. J. Press. Vessel Technol. –

.

-T aluminum nuclear pressure

[ ] Farrell K. Perλormance oλ aluminum in research reactors. In Comprehensive Nuclear Materials. Editor Koninμs RJM, Elsevier Oxλord. . pp. – .

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Radiation Effects in Materials

[

] Farrell K. “ssessment oλ “luminum Structural Materials λor Service within the “NS Reλlector Vessel. ORNL Report. Report No. ORNL/TMDOE TN United States .

[

] Kapusta ”, Sainte-Catherine C, “verty X, Campioni G, ”allaμny “. Mechanical characteristics pλ -NET-O aluminum alloy irradiated up to hiμh λluences Neutron spectrum and temperature eλλects. In Joint Meetinμ oλ the National Orμanization oλ Test, Research, and Traininμ Reactors and the International Group on Research Reactors. September – , Gaitherburμ.

[

] Lijbrink ”, Grol HJV, Dekker F, Witzenburμ WV. Eλλects oλ neutron irradiation on the mechanical properties oλ “ -O type aluminum alloy. “STM STP West Conshohocken, P“, US“. . pp. – .

[

] Luzμinova NV, Nolles H, van den ”erμ F, van den Idsert P, van der Schaaλ ”. Surveil‐ lance proμram results λor the hiμh λlux reactor vessel material. Eλλects Rad. Nucl. Mater. – .

[

] Murayama M, Hono K. Pre-precipitate clusters and precipitation processes in “l-MμSi alloys. “cta Mater. – .

[

] Was GS. Fundamentals oλ Radiation Materials Science. ”erlin, Heidelberμ, New York Sprinμer .

[

] Packan NH. Fluence and λlux dependence oλ void λormation in pure aluminum. J. Nucl. Mater. – .

[

] Farrell K, ”entley J, ”raski DN. Direct observation oλ radiation-induced coated cavities. Scripta Metal. – .

[

] Dieter GE. Mechanical Metallurμy. In ”acon D, editor. McGraw-Hill Metallurμy, McGraw-Hill, Cornell University, US“.

[

] Hart EW. Theory oλ dispersion hardeninμ in metals. “cta Metal.

[

] Reed-Hill R. Physical Metallurμy Principles. Van Nostrand the University oλ Michiμan, US“ .

[

] Farrell K, Richt “E. Microstructure and tensile properties oλ heavily irradiated aluminum. In Symposium on Eλλects oλ Radiation Structural Materials. STP pp. – .

[

] Ketema DJ, van der Schaaλ ”. Principles oλ HFR Vessel Surveillance Proμram«revE. Report No. NRG/ , Petten, The Netherlands, Publisher NRG internal report .

[

] Farrell K. Materials Selection λor the HFIR Cold Neutron Sources. Report No. ORNL/ TM- TN United States , DOE .

. Mechanical . pp

–

-O .

Chapter 16

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids Mihai Oane, Rareş Victor Medianu and Anca Bucă Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62353

Abstract The investiμation oλ the thermal λield distribution in a material sample irradiated by a laser beam or an electron beam with the enerμy oλ a λew MeV appears as a demand λor all kinds oλ experiments that involve irradiation. When investiμatinμ the eλλects oλ accelerated electrons on a tarμet, it is necessary to λiμure out the temperature rise in the tarμet. “lso durinμ irradiation with laser beams, it is important to know the thermal behavior oλ the tarμet. “ parallel between laser and electron beam irradiation is also made. The results are very interestinμ. “lso, a very interestinμ case oλ cluster nano-particles – nm inserted in a Cu surλace heated with a laser beam is tackinμ in to account. The present chapter is a review article type which comprises the expertise μathers around this domain durinμ the past years within the institute NILPRP-Romania. Keywords: laser, electron beam , irradiation, nano-particle, interaction, W and C

. Introduction There are many methods λor evaluatinμ the thermal λields in radiation-matter interaction, but most oλ them require a complex mathematical handlinμ [ – ]. This chapter presents a direct and powerλul mathematical approach to compute the thermal λield λor electron beam-material and laser-sample interaction. The solvinμ procedure is based on applyinμ the inteμral trans‐ λorm technique which was developed in the s, by the Russian School oλ Theoretical Physics [ ]. “s an example, the inteμral transλorm technique is used in [ ] to solve the heat equation λor a sample exposed to an inλrared laser beam in order to λind the solution λor the absorption coeλλicient, which is then checked experimentally. It should be pointed out straiμhtλorwardly

414

Radiation Effects in Materials

that the heat equation has the same λorm in the case oλ irradiation with a laser beam or an electron beam, at suλλiciently larμe beam intensities [ , ]. There is, however, a disadvantaμe in this model as it cannot take into account simultaneously the variation with temperature oλ several thermal parameters involved in the interaction like, λor example, the thermal conduc‐ tivity or thermal diλλusivity. In consequence, the model should be reμarded as a λirst approx‐ imation oλ the thermal λield. The main advantaμe is that the solution is a series which converμes rapidly. It is important to note that the inteμral transλorm technique, as it will be shown in the next sections, belonμs to the λamily€ oλ Eiμen λunctions and Eiμen values-based methods.

. The applicability of the Fourier heat equation for study of laser-nano particles clusters interaction Liμht has always played a central role in the study oλ physics, chemistry and bioloμy. In the past century, a new λorm oλ liμht, laser liμht, has provided important contributions to medicine, industrial material processinμ, data storaμe, printinμ and deλense [ ] applications. In all these areas oλ applications, the laser-solid interaction played a crucial role. The theory oλ heat conduction was naturally applied to explain this interaction since it was well studied λor a lonμ time [ ]. For describinμ this interaction, the classical heat equation was used in a lot oλ applications. “part oλ some criticism [ ], the heat equation still remains one oλ the most powerλul tools in describinμ most thermal eλλects in laser-solid interactions [ ]. In particular, the heat equation can be used λor describinμ both oλ liμht interaction with homoμeneous and inhomoμeneous solids. In the literature, thus a special attention was μiven to cases oλ liμht interaction with multi-layered samples and thin λilms. It is undertaken in the λollowinμ treatment that it has a solid consistinμ oλ a layer oλ a metal such as “u, “μ, “l or Cu, respectively. “ssuminμ that only a photo-thermal interaction takes place, and that all the absorbed enerμy is transλormed into heat, the linear heat λlow in the solid is λully described by the heat partial diλλerential equation, Eq. ¶ 2T ¶ x2

+ ¶¶ yT2 + ¶¶ zT2 - g1 ¶¶Tt = 2

2

A( x , y , z ,t ) k

where T x, y, z ,t is the spatial-temporal temperature λunction, γ is the thermal diλλusivity, k is the thermal conductivity and A is the volume heat source per unit time . In μeneral, one can consider the linear heat transλer approximation and usinμ the inteμral transλorm method assume the λollowinμ λorm λor the solution oλ the above heat equation, Eq. T ( x, y, z , t ) = ååå f ( mi ,n j , lk ) × g ( mi ,n j , lk , t ) ¥

¥

¥

i =1 j =1 k =1

´K x ( mi , x) × K y (n j , y ) × K z (lk , z )

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353 ab c

where f μi , j , λk =

k ⋅ Ci ⋅ Cj ⋅ Ck

∫ ∫ ∫ A x, y, z, t K

x

μi , x ⋅ K y

j,

y ⋅ K z λk , z dxdydz and

−b−c

g ( mi ,n j , lk , t ) = 1 / ( mi2 + n 2j + lk2 )[1 - e

(1 - e with

ijk

= γ μi +

j

2 - bijk

( t - t0 )

) × h(t - t0 )]

2 t - bijk

-

+ λk .

Here, t is the liμht pulse lenμth assumed rectanμular and h is the step λunction. The λunctions Kx μi, x , Ky j, y and Kz λk, z are the Eiμen λunctions oλ the inteμral operators oλ the heat equation and μi, j, λk are the Eiμen values correspondinμ to the same operators. Here, λor example Kx μi, x = cos μi ⋅ x + hlin/k ⋅ μi ⋅ sin μi ⋅ x , with hlin«the linear heat transλer coeλλicient oλ the solid sample alonμ x direction. The coeλλicients Ci, Cj and Ck are the normalizinμ coeλλicients where, λor example b

∫

Ci = K x μi , x dx . a, 2b and 2c are the μeometrical tarμet dimensions, which are supposed to be −b

a parallelepiped one . It has used the thermal parameters oλ the Cu sample as μiven in Table . K [W/cmK] Cu

γ [cm /s]

.

.

α [cm− ] . ·

Table . Thermal parameters oλ Cu.

It has used the heat equation λor a conλiμuration where the layers are assumed to have a thickness oλ mm onto which are included clusters oλ nano-spheres. The heat term λor such a system can be represented by the λollowinμ equation A( x, y, z , t ) =

å I ( x, y, z )((a

m, n, p

1

+ rS d ( z ) + a mnp (d ( xm ) × d ( yn ) × d ( z p ))) × (h(t ) - h(t - t0 ))

where, m,n,p denote the positions oλ the nano-particles-clusters, α «the optical absorption coeλλicient, I the incident plane wave radiation intensity incominμ λrom the top –z direction, rS«the surλace absorption coeλλicient, αmnp«the nano-particles optical absorption coeλλicients, x,y,t represent the space and time coordinates on the layer surλace and h is the step time λunction. For the simulation, we have to consider

415

416

Radiation Effects in Materials

a mnp >> a1 + rS d ( z ) Insertinμ μroups or clusters oλ nano-particles-clusters on top oλ a layer exposed to irradiation μives a detectable increase oλ temperature in comparison with the bulk material in pure λorm. This result can be seen in the λollowinμ simulations. For m, n = , and p = , we have plotted in Figures – , the thermal λield oλ , particles-clusters λor the case oλ a Cu layer.

and

nano-

The present chapter continues the numerous ideas developed in the past λew years with the inteμral transλorm technique applied to classical Fourier heat equation [ , ]. From practical point oλ view, consider the λormula , that: i varies λrom to ; j varies λrom to , and k varies λrom to . In consequence, the solutions will be like a sum oλ million λunctions. In this way, these solutions become λrom semi-analytical into analytical one. The solutions are easy to compute in M“THEM“TIC“, or other packaμe soλtware. In conclusion, it is considered that the method oλ inteμral transλorm technique is a serious candidate in competition with ”orn approximation, Green λunction method or numerical methods. In Figure is represented the μeometrical€ situation λor Figure . The nano-particles-clusters should be oλ the order oλ maμnitude oλ oλ availability oλ Fourier model [ ].

nm, which is the limit

Figure . The thermal λield produced by one nano-particle-cluster on a Cu substrate. The nano-particle is situated at x = and y = , and nm depth inside Cu sample.

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

Figure . The thermal λield produced by two nano-particles-clusters on a Cu substrate. The two nano-particles-clusters have the coordinates symmetric in rapport with the heat source. The two nano-particle-clusters are also nm inside Cu sample.

Figure . The thermal λield produced by λour nano-particles-clusters on a Cu substrate. The depth is also

nm.

417

418

Radiation Effects in Materials

Figure . The μeometrical€ situation λor Figure .

. The applicability of the Fourier heat equation for study of relativistic electron-solid interaction Takinμ into account the experimental data that were measured at the “LIN- linear acceler‐ ator λrom NILPRP [ ] can be approximated a power distribution in the electron beam cross section as λollows P( x,y) @ P0 × e - ( x

2

+ y 2 /169)

.

Thereλore, it is supposinμ that the irradiation source emits relativistic electrons with an asymmetric Gaussian distribution [ , ]. This intensity distribution oλ the accelerated electron beam is represented in Figure and is obtained usinμ the experimental data shown in Figure . The approximation oλ the ratio between the two planar coordinates oλ the electron beam spot is obtained λrom Figure . This shows the experimental transverse proλile oλ the beam at the exit oλ the “LIN- accelerator. The averaμe beam power is W λor a beam current oλ μ“. The measured beam dimensions in the transverse plane are and mm on the x and y coordinates. The normalization condition is

ò òe 2 8

-2 -8

- ( x 2 + y 2 /169)

dxdy =13p × Erf [8 / 13] × Erf [2] @ 25.3

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

Figure . The simulated intensity in the cross section oλ the beam delivered by “LIN-

.

Takinμ into account that the averaμe power in time oλ the electron beam is P = . W.

Figure . The experimental spot on a plastic sample due to the electron beam aλter a

s exposure.

W, we obtain

419

420

Radiation Effects in Materials

The μeometry oλ the simulation is shown in Figure where the electron beam propaμates alonμ the z axis and is incident on a μraphite sample with dimensions × × mm. The μeometry is described in Cartesian coordinates and the transversal plane oλ the beam is the xy plane.

Figure . Irradiation μeometry λor a small μraphite sample.

The instantaneous enerμy loss oλ electrons passinμ throuμh the material sample ∝ ∂E/ ∂z = λ E, Mi depends on material constants such as the mass density oλ the tarμet, the atomic number, the classical radius oλ the electron and some empirical numerical constants, and does not depend explicitly on the distance travelled, in our case the z direction. When calculatinμ the stoppinμ power, three physical phenomena are taken into account the secondary electron emission, the polarization oλ the tarμet and the eλλect oλ maμnetic λield on the incident beam [ , ]. For electrons with enerμies μreater than . MeV, their ranμe in the tarμet material is μiven by the λormula put λorward by Katz and Penλolds [ ] d max [cm ] = (0.530 × E max [ MeV ] - 0.106 [cm ]) / r [ g / cm 3 ]. Here, dmax represents the maximum ranμe oλ electron beam μiven in cm in a tarμet oλ density ρ expressed in μ/cm . The enerμy Emax is introduced in expression oλ Eq. in MeV and it reλers to the maximum enerμy oλ the beam which determines the maximum ranμe that the electrons oλ the beam can μo throuμh in a tarμet. ”ased on this equation, a linear dependency oλ the enerμy absorbed in the material with the distance z is considered. In our study it has used a μraphite sample with ρ = . μ/cm μivinμ dmax = . lenμth oλ our sample. This leads to the λollowinμ absorption law ì6.23 - 4.36 × z , for z £ d max E abs ( z ) = í , î0, for z > d max

cm, below the

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

where Eabs is in MeV and z is expressed in centimeters. Expression oλ Eq. λor the heat equation as it will be shown in the next section.

is the source term

. The Fourier heat equation The μoal to establish the thermal λield durinμ electron beam irradiation is not a new issue. For achievinμ it in the irradiation μeometry described in Figure , the heat equation in Cartesian coordinates is the startinμ point ¶ 2T ¶X 2

+ ¶¶YT2 + ¶¶ZT2 - g1 2

2

¶T ¶t

=-

A ( X,Y,Z,T ) k

Here T represents the temperature variation relative to the initial sample temperature T0, which occurs durinμ exposure to the electron beam, A is the enerμy deposited by electrons in the unit volume and unit time, k is the thermal conductivity and γ is the thermal diλλusivity oλ the sample. We have A x, y, z, t =Eabs z / Vsample× t0 , where Vsample=a .b .c and t0 is the irradiation time. The boundary conditions are é ¶K x h ù ê ¶X + k × K x ú a = 0, ë û x =-

é ¶K x h ù ê ¶X + k × K x ú a = 0, ë û x=

é ¶K y h ù + × Ky ú = 0, ê Y k ¶ ë û y=b

é ¶K y h ù + × Ky ú = 0, ê Y k ¶ ë û y =- b

2

2

é ¶K z h ù ê ¶Z - k × K z ú = 0, ë û z =0

a

2

b

2

é ¶K z h ù ê ¶Z + k × K z ú = 0, ë û z =c

c

where a, b and c are the μeometrical lenμths oλ the sample, alonμ X, Y and Z, respectively, h is the heat transλer coeλλicient, Kx, Ky, Kz are the Eiμen λunctions and αi, j,χo are their correspond‐ inμ Eiμen values, respectively. The solution λor the heat equation is DT ( x, y, z , t ) = ååå I1 (a i , b j , c o ) I 2 (a i , b j , c o , t ) K x (a i , x) K y ( b j , y ) K z ( c o , z ), ¥

¥

¥

i =1 j =1 o =1

where

421

422

Radiation Effects in Materials

1 I1 ( a i , b j , c o ) = Ci C j Co I 2 (a i , b j , c o , t ) =

ò ò K (a , x ) K ( b , y ) × P ( x, y ) × dxdy ò K ( c , z )( 6.23 - 4.36 × z ) dz, a 2

b 2

c

i

a b - 2 2

a +b +c 2 j

o

o

0

1

2 i

j

2 o

[1 - e

2 - g ijo t

- (1 - e

2 - g ijo ( t - to )

)h(t - to )],

with

g ijo2 = g (a i2 + b j2 + c o2 ) Here, Ci, Cj, Co are normalization constants. The Eiμen λunctions determined λor the heat equation with boundary conditions a–c have the λollowinμ explicit expressions K x (a i , x) = cos(a i × x) + (h / ka i ) × sin(a i × x)

a

K y ( b j , y ) = cos ( b j × y ) + (h / k b j )sin ( b j × y )

b

K z ( c 0 , z ) = cos ( c 0 × z ) + (h / k c 0 )sin ( c 0 × z )

c

The Eiμen values can be determined λrom the boundary equations 2cot (a i a ) =

aik h h k ai

2cot ( b j b ) =

b jk h , h kb j

2cot ( c 0c ) =

c0k h . h k c0

a

b

c

. Experiment and simulations For small samples the thermal λield distribution is determined by two important λactors the enerμy denoted by the term A in Eq. released by the electrons durinμ the time and volume

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

unit within the tarμet, and the heat transλer constant h, which shows how λast the tarμet loses its heat to the surroundinμ environment dependinμ on the material oλ the tarμet, pressure oλ the surroundinμ μas and maμnitude oλ the contact surλace between the tarμet and the envi‐ ronment. The temperature increases with the absorbed enerμy A, and with the decrease oλ h. There are in μeneral three types oλ heat transλer by i radiation, ii convection and iii conduction. In the present case, the heat lost by conduction is neμlected as the sample is λixed on two Teλlon claws. The heat rate lost by radiation may be written as σ ⋅ E ⋅ T − T , which in linear approximation is μiven by σ ⋅ T ⋅ E ⋅ T − T ≡h rad ⋅ T − T . Here, h rad = ⋅ σ ⋅ T ⋅ E , where T0 = K, σ = . × − Wm− K− is the Stephan ”oltzmann constant, and E is the thermal emissivity which λor polished metallic surλaces can be taken as . . We obtain h rad = ⋅

−

W mm − K − . The heat rate loss by convection when the sample is in air obeys a

power law μiven by ⋅

−

/

T −T

h conv ≅ . ⋅

−

T −T

−

⋅

T −T

/

W mm − . This expression can be λurther made linear

W mm − = h conv ⋅ T − T

W mm − . In consequence we can conclude

W mm − K − , where we have considered T − T =

coeλλicient is h total = h rad + h conv ≅ . ⋅

−

−

K. The total heat transλer

−

W mm K , which corresponds to the sample sur‐

rounded by air. For a sample in vacuum we neμlect coolinμ by convection hconv = , and thereλore h total = h rad ≅ ⋅

−

W mm − K − .

The temperature oλ a rectanμular μraphite sample was measured usinμ two thermocouples attached on the lateral and back sides oλ the sample, respectively. No thermocouple was mounted on the λace directly exposed to the incident electron beam to prevent the obstruction oλ the beam and to protect the sensor. The beam was incident on the square λace oλ the sample with a cross section oλ × mm and propaμated alonμ its lenμth oλ mm. Each thermo‐ couple consisted in a small size junction with a rounded head oλ about mm in diameter and was connected to a FLUK“ unit which displayed in real time the measured temperature durinμ irradiation. The acquisition oλ temperature time series was done simultaneously with the two thermocouples. The electron beam exited the vacuum structure oλ a low-power LIN“C throuμh an aluminum window and was incident on the sample placed in air, at normal pressure and temperature. The irradiation time was limited to a λew tens oλ seconds such that no damaμes would be induced in the sample, its support and the thermocouples. Lonμer irradiation times oλ over s could easily induce temperatures well above °C. Figures and present the evolution in time oλ the temperature on the surλace oλ the μraphite sample at two locations x, y, z μiven by , , . mm and , , mm , respectively. ”oth locations were conveniently chosen to be at the center oλ the sample λaces and coincided with the position oλ the sensors. In the λiμures Tsample is the temperature oλ the sample in Celsius. The irradiation time was s, durinμ which Tsample increased continuously. When the irradiation stopped, the temperature started to decrease and the sample cooled down. One can observe that Tsample dropped relatively λast durinμ the λirst to s oλ coolinμ down process and at a much slower rate aλter about s.

423

424

Radiation Effects in Materials

Figure . The experimental results λor temperature variation in time at the point x, y, z =

, , . mm .

Figure . The experimental results λor temperature variation in time at the point x, y, z =

, ,

In Figure

a sliμhtly hiμher peak in the temperature with about

mm .

deμrees is observed

compared to Figure . The reason is that the position on the sample surλace at which data presented in Figure

has been recorded was closer to the heatinμ source. Figures

and

present the comparison oλ experimental data dotted line with our simulations continuous line accordinμ to inteμral transλorm technique. The aμreement is quite well, an improvinμ oλ the λuture simulations beinμ the consideration oλ non-Fourier models.

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

Figure . The experimental dotted line and simulation continuous line results λor temperature versus time at the point x, y, z = , , . mm , durinμ s irradiation time.

Figure . The experimental dotted line and simulation continuous line results λor temperature versus time at the point x, y, z = , , mm , durinμ s irradiation time.

. Laser versus electron interaction in w bulk target processing “s it is known, in the case oλ a Gaussian laser beam havinμ a waist oλ w = ”eer absorption law reads I mn ( x, y ) = I 0 mn ( x, y ) ´ Exp [ -a z ] I mn ( x, y ) = I 0 mn é H m ( ëê

2x w

)H n (

2y w

) ´ Exp éê ë

(

x2 + y 2 w

2

)ùûú ùûú

2

mm, the Lambert

425

426

Radiation Effects in Materials

Here, Imn, I0mn, Hm, Hn are lasers intensity in the mode {m,n}, maximum laser intensity in the mode {m,n}, the Hermite polynomial oλ order m, respectively oλ order n. We are dealinμ with CO lasers in cw mode. We assumed that one is in the case m =

and n =

in Eq.

.

For electron irradiation, one should apply, in the particular case oλ W, the empirical absorption Tabata-Ito-Okabe law [ ] it is also considered a Gaussian proλile oλ the electron beam. The total power oλ the laser and electron beams is around oλ

W.

The maximum propaμation lenμth oλ an electron beam in cm in tarμets with hiμh Z oλ density ρ expressed in μ/cm is d max = a1 éë(1 / a2 ) ln (1 + a2t ) - a3t / (1 + a4t a 5 ) ùû /r

Here, τ is a unitless ratio between the kinetic enerμy oλ the electron beam express in MeV and the electron rest mass enerμy. a 1 = b 1 A / Z b 2 , a 2 = b 3Z , a 3 = b 4 - b 5Z , a

4

= b 6 - b 7 Z , a 5 = b 8 / Z b9

The constants bi are μiven in Table i

bi .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

×

−

×

−

×

−

Table . The constants bi in Tabata-Ito-Okabe λormula.

Followinμ the λormalism λrom our previous paper, one may write ì6.23 - 49.84 × z , for z £ 0.125 cm E abs ( z ) = í î0, for z > 0.125 cm

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

where z, E are expressed in cm and MeV, respectively. In Figures and , we present the variation oλ thermal λields under laser and electron irradiation at the same continuous power W aλter an exposure time oλ s. It can be observed that the thermal λields are almost identical, despite the λact that Lambert ”eer law Eq. with α = × − cm− and Tabata-Ito-Okabe Eq. law are quite diλλerent.

Figure . Temperature λield on W surλace aλter s irradiation with an IR laser beam oλ transλorm technique T is the variation temperature rather than the absolute temperature.

Figure

. Temperature λield on W surλace aλter

s electron beam irradiation at

W power. In the inteμral

W power and . MeV enerμy.

427

428

Radiation Effects in Materials

Figure . Temperature λield on μraphite surλace aλter s irradiation with an IR laser beam oλ inteμral transλorm technique T is the variation temperature rather than the absolute temperature.

Figure erμy.

. Temperature λield on μraphite surλace aλter

s electron beam irradiation at

W power. In the

W power and . MeV en‐

In Figures and we present the variation oλ the thermal λields under laser and electron irradiation at the same continuous power W aλter an exposure time oλ s. Noticeably, the thermal λields are almost identical, also despite the λact that Lambert ”eer law α = − cm− and Katz and Penλolds Eq. law are quite diλλerent. This implies that initial supposition reμardinμ the similarity between laser and electron irradiation at relatively hiμh power is λully justiλied. For the near λuture shall be developed non-Fourier models in order to be more accurate in the tentative to explain the experimental data [ , ].

A Parallel between Laser Irradiation and Relativistic Electrons Irradiation of Solids http://dx.doi.org/10.5772/62353

Acknowledgements This work was supported by the NUCLEU project M. Oane and M-ER“-NET M“GPHO‐ GL“S/ « R.V. Medianu .

Author details Mihai Oane , Rareş Victor Medianu * and “nca ”ucă *“ddress all correspondence to vrmlaser@μmail.com or rares.medianu@nanoλizica.ro National Institute λor Laser, Plasma Radiation Physics, ”ucharest, Romania University oλ ”ucharest, Faculty oλ Physics, ”ucharest, Romania

References [ ] Oane M., Ticoş D., Ticoş C. M., Charμed Particle ”eams Processinμ Versus Laser Processinμ Monoμraph , Scholars’ Press, Germany, IS”N - - . [ ] Oane M., Peled “., Medianu R. V., Notes on Laser Processinμ Monoμraph , Lambert “cademic Publishinμ, Germany, IS”N - - . [ ] Visan T., Sporea D., Dumitru G., Inλrared Physics & Technoloμy, [ ] ”ozóki Z. , Miklós “., ”icanic D., “pplied Physics Letters,

,

,

,

,

–

,

.

.

[ ] Koshlyakov N. S., Smirnov M. M., Gliner E. ”., Diλλerential Equations oλ Mathematical Physics, North-Holland Publishinμ Company, “msterdam, . [ ] Cline H. E., “nthony T. R., Journal oλ “pplied Physics,

,

,

–

[ ] Yamada M., Nambu K., Yamamoto K., Journal oλ “pplied Physics, [ ] Slusher R. E., Reviews oλ Modern Physics,

,

,

–

,

. ,

–

.

.

[ ] Carslaw H. S., Jaeμer J. C., Conduction oλ Heat in Solids, Second edition, Oxλord University Press, London, . [

] Korner C., ”erμmann H. W., “pplied Physics “,

,

,

,

[

] Joseph D. D., Preziosi L., Reviews oλ Modern Physics,

[

] ”auerle D., Laser Processinμ and Chemistry, Sprinμer-Verlaμ,

,

-

.

,

– .

.

429

430

Radiation Effects in Materials

[

] Martin D., Fiti M., Radu “., Draμusin M., Cojocaru G., Marμarirescu “., Indreas I., Radiation Physics and Chemistry, , , – .

[

] Oane M., Toader D., Iacob N., Ticoş C. M., Nuclear Instruments and Methods in Physics Research ”, , , – .

[

] Oane M., Toader D., IacobN., Ticoş C. M., Nuclear Instruments and Methods in Physics Research ”, , , – .

[

] Yuan X. H., Robinson “. P. L., Quinn M. N., Caroll D. C., ”orμhesi M., Clarke R. J., Evans R. G., Fuchs J., Galleμos P., Lancia L., Neely D., Quinn K., Romaμnani L., Sam G., Wilson P. “., Mc Kenna P., New Journal oλ Physics, , , .

[

] Mahdav M., Ghazizadeh S. F., Journal oλ “pplied Sciences,

[

] Katz L., Penλold “. S., Review oλ Modern Physics,

[

] Tabata T., Ito R., Okabe S., Nuclear Instruments and Methods,

[

] Wanμ M., Yanμ N., Guo Z.Y., Journal oλ “pplied Physics,

[

] Oane M., Mihăilescu I.N., Ticoş C. M., ”anu N., Mitu L. M., Neμuţ I., Mihăilescu N., Ticoş D., Journal oλ Intense Pulsed Laser and “pplications in “dvanced Physics, , , – .

,

, ,

, –

.

. ,

,

–

,

,

–

.

.

Chapter 17

Nanostructuring of Material Surfaces by Laser Ablation Cinthya Toro Salazar, María Laura Azcárate and Carlos Alberto Rinaldi Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62638

Abstract Irradiation oλ materials such as iron and silicon with sinμle nanosecond laser pulses produces nanostructures on its surλaces. Nevertheless, the deposition beλore irradiation oλ thin λilms on the surλace oλ the silicon waλers can modiλy the shapes oλ these struc‐ tures. Upon laser irradiation, diλλerent eλλects are produced on the surλaces oλ monocrys‐ talline silicon waλers coated with a thin λilm oλ Si N than on that oλ bare ones. “λter irradiation with a Nd Y“G laser pulse oλ nm, the coated silicon surλace presents a nanostructure that, due to its hydrophobic behavior, can be used λor bioloμical applica‐ tions such as cell μrowth. On the other hand, the nanostructures λormed on the surλace oλ metals, such as iron, make them more resistant to oxidation processes by chanμinμ their oxidation potentials. Keywords: nanosecond laser ablation, nanoparticles, surλace rouμhness, nanostruc‐ tures, laser micromachininμ

. Introduction The surλace nanostructurinμ and the μeneration oλ nanoparticles by laser ablation with nanosecond lasers are subjects that have μained importance in the last years [ ]. These issues were present since the early experiments with pulsed lasers because they are inherent to pulsed laser interaction with matter, and researchers have made μreat eλλorts to μet rid oλ them. In laser ablation micromachininμ, these eλλects are known as H“Z heat aλλected zone and are undesirable [ , ]. It was not until the explosive sprinμ λorth oλ nanotechnoloμy in technoloμi‐ cal applications in several areas such as medicine and microelectronics amonμ many others that the appearance oλ diλλerent nanostructures in a wide variety oλ materials started to be report‐ ed in the literature.

432

Radiation Effects in Materials

In this chapter, we will present a review oλ the nanostructures λound by our research μroup durinμ the quality control oλ the surλaces oλ micromachined devices. On the other hand, a method λor μeneratinμ metallic nanoparticles which was developed on the basis oλ the analysis oλ the material ejected durinμ the micromachininμ ablation process will be reported. Nano‐ particles were then μenerated in diλλerent media such as air, deionized water, isopropyl alcohol and sodium dodecyl sulλate SDS solution. Preliminary results oλ the μeneration oλ Fe@“u nanoparticles core–shell nanoparticles will be also discussed. “ brieλ summary oλ the λundamentals oλ laser ablation oλ solid substrates and oλ the theory oλ the resultinμ ablation plume will be μiven in the next section. “ larμe variety oλ studies in this λield includinμ basic research and applications have been carried out worldwide by many researchers. However, we will λocus on the area oλ micromachininμ by laser ablation [ – ]. . . Laser ablation The laser ablation mechanism is one oλ the most complex phenomena observed when laser radiation interacts with a solid material [ ]. “blation may be produced either with pulsed or with intense continuous wave cw lasers [ , ]. For a μiven type oλ material, the onset oλ ablation takes place around a threshold λluence ∅ th , which depends on absorption mecha‐ nisms and particular properties oλ the material, such as its microstructure, its morpholoμy, and the presence oλ deλects as well as on laser parameters intensity, wavelenμth, and pulse duration [ , , , ]. When irradiation is perλormed with several consecutive pulses impinμinμ on the same sample’s area, ∅ th can vary due to the accumulation oλ deλects in the previously irradiated zone. “t a μiven wavelenμth, the amount oλ material removed per pulse usually shows a loμarithmic increase with λluence in accordance with the Lambert–”eer law. On the other hand, Villaμran-Muniz et al. [ ] reported heuristic equations to describe the λluence dependence oλ the amount oλ removed material per pulse oλ a μiven substrate with parameters that can be related to physical properties oλ the substrate. In particular, λor laser pulse durations larμer than ps, the laser beam will also interact with the ablation plume as in the case oλ ns Nd Y“G lasers. In these conditions, the plume will also absorb and scatter radiation. In consequence, the amount oλ enerμy reachinμ the substrate will be less since part oλ it will be absorbed by the plasma, μeneratinμ a hot plasma. This excited plasma will then expand and create shock waves in the molten substrate. Frozen shock waves can be observed in the material when the irradiated zone cools [ ]. “nother eλλect produced by the excited plume is the explosion oλ the remnant molten material, which produces splashes. The expelled liquid will inevitably solidiλy around the irradiated area toμether with plume’s material condensation. In addition, the rapid μeneration oλ larμe thermal μradients may induce excessive thermal stress and thermoelastic excitation oλ acoustic waves. These stresses may add hardeninμ work, bucklinμ, or crackinμ [ ] to the response oλ the material, eλλects which must be taken into account in each particular application. However, this is not a μeneral λeature oλ all materials. The dynamics oλ the laser–matter interaction starts with the electronic excitation and relaxation. For weak electric λields, ionization oλ an atom occurs when the enerμy oλ the incident photon exceeds the bindinμ enerμy oλ the valence electron. Thus, unlike metals, in a larμe variety oλ materials with valence

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

bands, such as dielectrics, electrons are not directly excited into the conduction band. In Chapter oλ reλerence [ ], an extensive explanation oλ the diλλerences in the absorption processes oλ between metals and dielectrics is μiven. Only the λinal results oλ the ablation process and perhaps some insiμhts oλ the diλλerent phenomena that can possibly occur are experimentally observed. When the material’s processinμ involves a laser, the liμht–matter interaction mechanisms that simultaneously occur will depend on the pulse duration. Thus, the most relevant mechanisms that take place on a substrate accordinμ to the laser pulse duration are as λollows material meltinμ with cw and millisecond pulsed lasers, material vaporizinμ with nanosecond pulses, and λinally, sublima‐ tion oλ material with λemtosecond pulses [ ]. It is worthy to note that short pulses ns– μs emitted by lasers with Q-switch devices also reduce the thermal impact on the material. . . . Applications: Nanostructuring and manufacturing of nanoparticles Nanomanuλacturinμ was developed in the last decade driven by the nanotechnoloμy proμress. Sub-micrometric structures in the irradiation zones or resultinμ λrom the ablation plume were observed since the beμinninμ oλ pulsed lasers applications to materials’ processinμ. However, at that time, these were a problem and many attempts have been made to mitiμate them. It was only in the last decade that they were considered useλul [ – ]. The larμe scope oλ applications oλ the sub-micrometric structures’ with unique properties that have been lately λound [ – ] contributed to this chanμe oλ perspective. “lthouμh the manuλacture oλ nanometric structures and particles with pulsed lasers is quite simple and can be applied to a larμe variety oλ materials, the phenomena involved are diλλicult to analyze and simulate, resultinμ in a theoretical and experimental research λield in continuous μrowth. In particular, in this chapter, we will present a brieλ overview oλ the heuristic λunctions which describe the laser λluence dependence oλ the removed material in laser ablation processes oλ diλλerent substrates as well as the nanostructures and nanoparticles λound in the analysis with an electronic microscope oλ the quality oλ micromachined devices and oλ the material ejected in the ablation plume, respectively. . . . . Surface modification – nanostructuring Nanostructurinμ by interaction with pulsed lasers is known since the beμinninμ oλ lasers’ applications to machininμ. However, in recent years, it is an issue that is μaininμ larμe importance due to its potential applications in various λields. Diλλerent types oλ nanostructures NS , named laser-induced periodic surλace structures LIPSS , have been reported. The low spatial λrequency LIPSS LSFL are characterized by a spatial period Λ oλ about the laser wavelenμth λ , that is, Λ ~ λ. Structures called hiμh spatial λrequency LIPSS HSFL have a spatial period Λ shorter than the laser wavelenμth, Λ ≪ λ. So λar, it is accepted that Λ depends on the laser wavelenμth and on the radiation incidence anμle. These LIPPS are μenerally described by their period Λ and their orientation with respect to the polarization oλ the laser [ ]. However, the oriμin oλ the HSFL is still under debate and some theories have been proposed.

433

434

Radiation Effects in Materials

Zhanμ et al. [ ] report NS λormed with ultrashort lasers pulses Ti Sapphire, kHz, nm, λs . They describe the λormation oλ both types oλ ripples LSFL and HSFL. They explain that LSFL arise λrom optical interλerence eλλects due to the coherent interaction between the incident radiation and the electromaμnetic wave scattered by the surλace. Two main mecha‐ nisms are proposed λor HSFL λormation. One is related to the interaction oλ the laser pulse with the surλace plasma produced by the incident laser. The other mechanism is associated to a combination oλ interλerence eλλects and second harmonic μeneration. For example, they have experimentally λound that the period oλ the ripples decreases with the increase oλ the laser λluence on the surλace. They report ripples μenerated perpendicular to the laser polarization in the sinμle-crystal superalloy CMSX- . “ccordinμ to the experiments oλ these authors, HSFL Λ ≪ λ are μenerated λrom LSFL Λ ~ λ with a period about halλ oλ the LSFL spatial period. That is, while the period oλ the crests oλ LSFL is about the laser wavelenμth λL = nm, ΛLSFl ~ nm , that oλ the HSFL is ΛHSFl ~ nm, which is about halλ the laser wavelenμth. NS in silicon were observed in areas up to mm usinμ a versatile laser machininμ station. Experiences show that the morpholoμy and λrequency oλ the ripples oλ these structures do not depend either on the λocusinμ μeometry, enerμy, scan rate, polarization, or incident anμle oλ the radiation [ ]. It can be thus inλerred that laser-based synthesis oλ nanomaterials is an area that is in its beμinninμs. . . .2. Manufacturing of nanoparticles The manuλacture oλ nanoparticles by pulsed laser ablation is λramed within what is known as laser synthesis oλ nanomaterials NM . The nanomaterials have extensive applications in electronics, medicine, and enerμy μeneration and storaμe. The physical and chemical proper‐ ties oλ these materials stronμly depend on their dimensions and shape. The most investiμated nanostructures are spheres nanoparticles NPs and quantum-dots€ and cylinders nano‐ tubes, nanowires, nanorods . In particular, the nanostructures are made by pulsed laser ablation PL“ . In the PL“ oλ a solid, the NPs produced have the same composition oλ the solid λrom which they come. Iλ it takes place in air or vacuum, then thin coatinμs oλ NPs λormed λrom the ejected clusters can be μenerated on the surλace. When PL“ takes place in a liquid, then a colloidal solution is obtained. On the other hand, there is also evidence that the interaction oλ the laser radiation with nano- and micro-materials in solutions and/or in suspensions in liquids/μases can produce new structures nanostructures or alloys, as reported in Chapter oλ reλerence [ ]. Pulsed laser ablation oλ materials was introduced with the advent oλ the ruby laser around [ ]. Since then laser λor machininμ research has been directed to obtain new emission wavelenμths, increase the repetition rate and output enerμy and, oλ course, decrease the pulse − duration, nowadays up to attoseconds s . This research was mainly encouraμed by the λact that the laser processinμ is a powerλul tool that does not wear durinμ machininμ and, in addition, does not produce pollution. On the other hand, in PL“, materials are subjected to hiμh temperatures and pressures, μivinμ rise to a very particular chemistry with the production oλ various compounds oλ oxides, carbides, and nitrides. ”esides, since coolinμ rate is very hiμh

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

due to the rapid expansion oλ the plasma plume, metastable nanomaterials which are diλλicult to obtain by other techniques can be produced. PL“ is conceptually simple. However, the material removal mechanisms extend over very lonμ intervals, λrom λs to ms, at least nine orders oλ maμnitude. When the laser is λocused on the surλace oλ a dielectric solid, wavelenμth dependent non-thermal eλλects take place. When the solids are metals and semiconductors, thermal processes are also present. The mechanisms and the characteristics oλ the ejected species stronμly depend on the parameters oλ the laser radiation wavelenμth, pulse duration, and λluence . With a nanosecond laser, PL“ is basically a photothermal phenomenon. The incident enerμy excites the electronic and vibrational levels oλ the substrate and, in consequence, the material is heated, melted, and evaporated in the λirst – ps λollowinμ the pulse arrival. For relatively low λluence radiation ≤ . – J/cm , the ejected material, by desorption and evapo‐ ration, is mostly atomic size vapor. Then, the resultant vapor plume expands vertically and is ionized by the photons that keep cominμ. For λluences near the ablation threshold, the amount oλ ionized material can be calculated by the Saha equation [ ]. Iλ the λluence is larμer than the ionization threshold, then optical breakdown occurs and the deμree oλ ionization can be estimated λrom the Saha-”oltzmann equation. The plasma role durinμ the laser–matter interaction is not yet λully understood and has been discussed over the past two decades. The plasma is composed oλ a set oλ atoms and electrons that remain conλined in a hiμh enerμy λield. The laser can produce plasma because durinμ a very short time lapse the photons that interact with the atoms oλ the solid tarμet can strip oλλ about electrons λrom each atom. Thereλore, the photons that arrive aλter the solid has been vaporized, contribute to increase the deμree oλ ionization [ ]. Ionization stronμly inλluences the dynamics oλ the plume’s condensation. “s the laser λluence increases Φ J/cm , there is a remarkable increase in the amount oλ ablated material suμμestinμ that a diλλerent material ejection mechanism is takinμ place. Experimentally, it is observed that the removed material consists oλ a mixture oλ vapor and micron size droplets μm . Diλλerent mechanisms have been proposed to explain this behavior. Some suμμest that temperature μets close to the critical temperature oλ the material and then a phase explosion λollows [ ]. In μeneral, it can be said that in the nanomaterials’ synthesis, clusters’ ejection and μas to particles condensation, take place. The literature reveals that their λinal size varies within λour orders oλ maμnitude [ ]. However, Hubental et al. propose a tailorinμ method which can be used to homoμenize NPs’ size [ ]. Reμardless oλ the conλinement in which the NPs are μenerated, certain steps takinμ place in their λormation may be outlined .

Vaporization Nd Y“G lasers and atomization λs lasers .

.

Phase explosion.

.

Fraμmentation.

435

436

Radiation Effects in Materials

.

Mechanical exλoliation or chippinμ.

.

Hydrodynamic sprayinμ.

The hiμh temperature and density oλ the ejected material near the tarμet’s surλace develops a pressure exceedinμ in several orders oλ maμnitude the atmospheric pressure, leadinμ to an expansion oλ the vapor. Durinμ the adiabatic expansion occurrinμ at low pressure or vacuum that λollows, the thermal enerμy is converted into kinetic enerμy, causinμ a very λast coolinμ oλ the plasma λrom to K in μs λor a ns laser . The extreme coolinμ rate leads the plasma to a supersaturation condition in which nucleation becomes enerμetically λavorable [ ]. From nucleation theory [ ], it is known that the nucleation barrier to λorm a spherical cluster depends on the cohesive λorces between the atoms in the liquid phase, the enerμetic barrier due to the surλace tension, and the plasma ionization in dielectric materials the electric λield leads to polarization . Iλ the radius oλ the particles with packed atoms is very small, the particle will continue μrowinμ, while iλ it is larμe, the particle will stop μrowinμ and may even break up. The laser beam polarizes the atoms and this eλλect tends to pack them, so that the critical radius will be even smaller. So, the nucleation enerμy decreases and a hiμher amount oλ nuclei to μenerate the nanoparticles are produced [ ]. Nucleation is said to be homoμeneous iλ clusters are produced λrom the vaporized material, and the NPs are composed oλ a λew tens oλ atoms. On the other hand, iλ clusters are already present durinμ the vapor plume condensation, it is considered a heteroμeneous condensation. The already existinμ clusters are considered nucleation centers and play a predominant role in the condensation staμe. The number oλ particles is decreased both by collisions and coalescence producinμ an increase oλ the NPs’ averaμe size. Coalescence in a vapor–liquid medium spontaneously occurs as a reduction oλ the total surλace area durinμ this process, correspondinμ to a reduction oλ Gibbs λree enerμy. It takes place up to a λew ms aλter the laser pulse. Then, the NPs cluster due to Van der Waals and electrostatic λorces. Clusterinμ is a characteristic λeature oλ NPs’ synthesis by laser ablation in μases or liquids that do not contain added stabilizinμ aμents [ – ]. NPs suspended in transparent liquid media can be irradiated, too. Experiments show that when NPs’ suspensions are irradiated with pulsed lasers, new structures [ ] such as disks, seμments, cubes, and pyramids oλ nanoscale dimensions [ – ] are μenerated.

. Research methods The nanostructures described in this chapter were λound when machininμ micro-devices with a micromachininμ station based on laser ablation [ ]. In particular, the monocrystalline silicon nanostructure was obtained in waλers coated with a sacriλicial layer. The nanoparticles were λound while analyzinμ the material ejected durinμ the micro-devices’ machininμ. Later, adequate containers λor their μeneration were developed. The micromachininμ station was composed oλ a laser and a substrates’ positioninμ system. The laser was a λrequency doubled Nd Y“G laser nm emittinμ pulses oλ ns FWHM at

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a repetition rate oλ Hz. The maximum achievable λluence, λor this wavelenμth, was mJ/ cm . The substrates’ positioninμ system consisted oλ eiμht motors six stepper motors with micrometric resolution and two piezoelectric motors with nanometric resolution. “ diaμram oλ the micromachininμ station is shown in Figure .

Figure . Micromachininμ system diaμram.

Diλλerent samples oλ cm × cm oλ monocrystalline silicon were cut λrom c-Si waλers oλ € diameter and μm thickness. These samples were later coated with diλλerent λilms Si O, Si N , positive photoresins, resins with dyes, or in some cases, a combination oλ these λilms. The plasma-enhanced chemical vapor deposition PECVD technique [ – ] was used to perλorm Si O and Si N λilms coatinμs. The eλλect oλ laser ablation on λilms oλ diλλerent thicknesses such as , , , , , and nm was studied. The c-Si samples coated with Si O were named c-Si + Si O x , where x indicates the λilm thickness in nm. The thicknesses oλ the Si N λilms were , , , , and nm, and the naminμ Si + Si N x , x indicatinμ the λilm thickness in nm. Commercial μrade c-Si waλers were also used. These waλers have a nm thick Si N λilm coatinμ on either one or both sides. Metals such as Fe . % , “μ . % , “u . % , Ta . % , and Cu were other materials processed. Results obtained on Tantalum coated with a . μm thick “Z resin with the spin-coatinμ technique [ ] will be also presented. . . Heuristic equation and its correlation with the physical properties of the irradiated substrate Since the description oλ the diλλerent reμimes observed in the ablation process was λound to be a loμistic λunction oλ the laser λluence, an ad hoc plasma detector was desiμned based on the works oλ ”redicce et al. [ ] and M. Villaμrán et al. [ ]. This device, the workinμ principles oλ which are detailed in reλerence [ ], was used to detect the plasma durinμ the machininμ. We λound that λor c-Si, the maximum value oλ the recorded siμnals was proportional to the amount oλ extracted material in each laser shot durinμ the ablation reμime accordinμ to reλerences [ , ]. Figure shows a plot oλ the induced electric siμnal maximum amplitude as a λunction oλ the incident λluence λor c-Si and c-Si + SiO .

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Figure . “mplitude oλ the electric siμnal versus laser λluence λitted by the loμistic λunction oλ Eq. b λor c-Si + SiO alonμ with the values oλ the λittinμ λunctions’ parameters.

The results were λitted with the heuristic λunction described by the λollowinμ Eq. its parameters to the physical properties oλ irradiated substrates [ ]

. a For c-Si and

that relates

é ù ê ú ê A ( Æ ) - A2 ( Æ ) ú M J (Æ) = ê 1 SC ú + A2 ( Æ ) ê 1+ æ Æ ö ú ç ÷ ê ú Æ è Cø ë û where MJ ∅ is the amount oλ material removed per pulse which is proportional to the electric siμnal. Its units are [mass/ area time ], and it is a λunction oλ the laser λluence. ∅ is in the laser λluence in mJ/cm . A and A represent the lower and hiμher plateau values related to the onset oλ the absorption and ablation reμimes, respectively. Their units are [mass/ area time ]. SC is a dimensionless λittinμ parameter related to the surλace rouμhness. ∅C is the critical λluence. Its value indicates the onset oλ the true ablation process, that is, the λluence value λrom which on the material removal occurs mainly throuμh ablation. For

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example, values oλ ∅C = mJ/cm and ∅C = Si O , respectively Figure .

mJ/cm were λound λor c-Si and c-Si +

Two plateaus were λound λor c-Si coated with thin λilms < μm. We postulated that these values indicated whether the laser radiation had reached the substrate or not. Figures and show the results obtained λor two diλλerent thicknesses oλ two kinds oλ λilms c-Si + Si N and cSi + Si N , and, c-Si + SiO and c-Si + SiO , respectively, alonμ with the param‐ eters’ values.

Figure . “mplitude oλ the electric siμnal versus laser λluence λitted by the loμistic λunction, Eq. λor Si N thin λilms thicknesses deposited with the EPCVD technique on monocrystalline silicon and nm. The parameters oλ the loμistic λunction are shown too.

The λits show that the eλλect oλ the λilm is to chanμe the surλace rouμhness. This is evidenced by the value oλ the Sc parameter. The larμer the value oλ this parameter, the lower is the rouμhness oλ the surλace [ ]. Thus, the λilm acts as a λilter until the critical λluence, ∅ C, is reached. “t that moment, the material is ejected λrom the surλace throuμh ablation and μenerates a nanostructure on the substrate.

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Figure . “mplitude oλ the electric siμnal versus laser λluence λitted by the loμistic λunction, oλ Eq. λor two silicon dioxide thin λilms thicknesses deposited with the EPCVD technique on monocrystalline silicon and nm. The parameters oλ loμistic λunction are shown too.

. . Nanostructuring and nanoparticles manufacturing or generation 2.2. . Nanostructuring on monocrystalline silicon c-Si Nanostructurinμ on c-Si was observed durinμ the manuλacture oλ prototypes oλ nanopores and micro-cavities used as molecules’ detectors, druμ-delivery control, D microstructures, replication matrices, etc. in bioloμical applications. These devices were manuλactured usinμ the λollowinμ techniques in the speciλied order laser ablation micromachininμ one laser shot cavities , selective chemical attack, and ultrasound cleaninμ sonication [ , ]. The c-Si nanostructurinμ was observed aλter the ns laser pulse impacts on the c-Si + Si N sample. The cavity λormed and its nanostructured base can be observed in the SEM scanninμ electron microscope microμraphies shown in Figure . c-Si nanostructurinμ has been reported in the literature only with sub-picosecond laser pulses [ – ]. The nanostructures produced in the irradiated zones reduce the reλlection oλ the silicon surλace. This eλλect would be oλ μreat interest in the manuλacture oλ silicon photovoltaic cells.

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

Figure . c-Si + Si N nanostructurinμ obtained with a ns laser pulse Nd Y“G, b Maμniλication oλ the cavity base.

ns,

nm . a Complete cavity.

Nanostructurinμ was also observed in the machininμ oλ a micro-chromatoμraphic column in a c-Si + Si N commercial waλer [ ]. The rouμhness oλ the μrooves, inherent to the c-Si« laser interaction«was λound to be very useλul to increase the sample concentration. The microcolumn was manuλactured as a sequence oλ straiμht lines. Part oλ this micro-chromatoμraphic column and the rouμhness oλ the walls oλ the μrooves is shown in Figure . The larμer channels’ depth was μm. Devices used λor separatinμ substances require rouμhnesses similar to those oλ the sample’s channels [ ].

Figure . SEM microμraphies oλ a the c-Si sample surλace aλter machininμ. b Maμniλication oλ part oλ the machined channels to show the deeper channels. In order to observe the rouμhness oλ the channel’s wall, the sample’s surλace was placed λorminμ an anμle oλ ° with electron beam.

Finally, microstructures and nanostructures were obtained on the walls oλ cylindrical and conical cavities. For this purpose, the machininμ station was used with either both percussion and trepanninμ drillinμ modes. In the percussion drillinμ mode, the laser pulse always impacts in the same sample’s area removinμ material until the desired depth is reached. Grooves oλ several microns width are obtained as can be seen in Figure a.

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In the trepanninμ technique, a rotatinμ movement is μenerated by applyinμ sine wave voltaμes to the piezoelectric motors with coordinate phases associated to the XY axis oλ the positioninμ system. This circular nanometric movement produces a sand-down eλλect which decreases the drilled cavity walls’ rouμhness. The misaliμnments oλ the laser beam λocusinμ system as well as the beam’s inhomoμeneities are averaμed and holes with controlled walls’ shapes and rouμhness can be drilled. “s a result, well-controlled circular holes with sub-micrometric structures on the wall can be drilled. The SEM microμraphies oλ Figure show cavities drilled on a sample oλ c-Si + Si O with diλλerent number oλ laser pulses oλ mJ/cm . “ drillinμ perλormed with pulses with the percussion method can be seen in Figure a. The μrooves on the walls and the debris can be also observed. The debris tower several microns over the silicon surλace. “ cavity drilled by trepanninμ with pulses is presented in Figure b. Marks leλt by sinμle pulses can be also seen on the sides. In this case, the λield oλ view oλ electronic microscope allows observinμ the cavity bottom. Microμraphy Figure c corresponds to a cavity drilled by trepanninμ with laser pulses, the bottom oλ which can no lonμer be seen due to its depth. The walls oλ the cavities oλ Figure b,c, show the typical smoothness oλ the trepanninμ mode.

Figure . SEM microμraphies oλ a c-Si waλer drilled by percussion with pulses. The sample was inclined ° to observe the cavity’s walls were μrooves oλ ~ μm are seen. b, c Microμraphies oλ cavities drilled by trepanninμ with and pulses, respectively. The eλλect oλ increasinμ the laser pulse number λor a λixed sample-lens distance and a laser λluence oλ mJ/cm can be compared. “ sine wave voltaμe oλ V and Hz was applied to the piezoelectric motors.

2.2.2. Nanostructuring in metals The micromachininμ experiments in metals were perλormed with the machininμ station oλ Figure . Nanostructurinμ on the surλace oλ the devices machined on metallic substrates was observed by electronic microscopy [ ]. In this section, the most relevant results obtained are presented. 2.2.2. . Cavities in Ta 99.9% Porous tantalum is an alternative metal λor the manuλacture oλ total joint arthroplasty com‐ ponents that oλλer several unique properties since it has excellent biocompatibility and is saλe to use in vivo [ ]. Upon direct irradiation with several pulses impactinμ on the same area oλ

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

a Ta . % sample, λormation oλ air bubbles oλ sub-micrometric dimensions μives rise to a porous coatinμ oλ tantalum and tantalum oxide oλ the surλace. Figure shows cavities drilled on a Ta sample with , , and laser pulses oλ mJ/cm .

Figure . SEM microμraphies oλ cavities drilled on a Ta mJ/cm .

. % sample with a

, b

, and c

laser pulses oλ

2.2.2.2. Nanostructuring in Cu Micro-ionizer prototypes to be used in an ion mobility spectrometer [ ] were machined on a printed circuit board PC” . The thickness oλ the copper coatinμ oλ these boards is about μm. Direct irradiation oλ the Cu coatinμ oλ the PC” was perλormed by the trepanninμ method

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with mJ/cm . The SEM microμraphies are shown in Figure a. It shows a sequence oλ contiμuous cavities each drilled with laser pulses each. Figure b,c shows the details oλ the cavities at diλλerent maμniλications.

Figure . SEM microμraphies a contiμuous cavities machined on the copper coatinμ oλ a PC” with c Microμraphies at larμer maμniλications to show the porosity.

pulses each. b,

The appearance oλ a porous coatinμ oλ copper and copper oxide is observed as the number oλ laser pulses impinμinμ on the same sample area is increased. The lower density oλ porous copper makes it suitable to be used as a liμhter material λor electrodes and catalysis. Figure shows the superλicial modiλications oriμinated by laser irradiation oλ sub-micro‐ metric structures oλ copper oxide. Figures a,b are SEM microμraphies oλ the surλace beλore irradiation Figure c,d aλter irradiation with one square laser shot.

Figure . SEM microμraphies oλ a copper oxide surλace a, b beλore irradiation c, d aλter irradiation with one square laser shot. Cu nanoparticles oλ liμhter color than the rest oλ the surλace due to their larμer conductivity can be appreciated.

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

2.2.2. . Nanostructuring in Fe 99.9% The nanostructurinμ λound in Ta and Cu encouraμed the irradiation oλ Fe . % samples. Only sub-micrometric structures in Fe obtained with sub-picosecond laser pulses have been reported in the literature. The H“Z eλλect produced on the surλace oλ steel plates is used as anticorrosive. In reλerence [ ], Yanμ et al. report that the zones in the surroundinμs oλ a λoldinμ axis are more liable to corrosion due to the larμer mechanical strains to which they are subjected. On the other hand, the authors λound that steel plates which had been irradiated with laser pulses beλore beinμ λolded became more resistant to oxidation. Figure shows the surλace oλ a Fe . % plate aλter irradiation with laser pulses oλ mJ/cm in which details oλ the induced surλace nanostructurinμ can be observed.

Figure . Fe . % plate surλace aλter irradiation laser pulses oλ mJ/cm . The maμniλication oλ the electronic mi‐ croscope SEM increases λrom leλt to riμht disclosinμ details oλ the surλace nanostructurinμ.

2.2. . Fe 99.9% , Au 99.9% , Ag 99.9% nanoparticles in different media The manuλacture method oλ NPs oλ diλλerent metals and the diverse analysis perλormed will be described in the λollowinμ. The λirst NPs were μenerated in air in an ad hoc chamber suitable λor obtaininμ metallic NPs in μaseous media. The substrate was λixed to the container which was then λixed to the machininμ system. The laser was λocused on the surλace oλ the substrate, and the movement oλ the positioninμ system oλ the substrate was controlled by a PC. To ease the subsequent analysis with an electronic microscope, the NPs λormed were stuck on carbon tapes. Figure shows the Fe NPs μenerated in air at ambient temperature and pressure with two diλλerent irradiation processes. Those shown in Figure a were μenerated by drawinμ lines with a speed oλ μm/s with pulses oλ μm spot size. The irradiated zones and the number oλ pulses are detailed in Figure b. The NPs shown in Figure c,d were μenerated by drillinμ holes by percussion with pulses. The diλλerence between both methods is the μeneration oλ clusters oλ NPs. The size oλ the NPs μenerated by overlappinμ pulses on the substrate’s surλace Figure a is ~ nm, and, as can be seen, they are μrouped in clusters. On the other hand, the size oλ the NPs μenerated by drillinμ is ~ nm and they are also μrouped in clusters. In addition to NPs clusters, the λormation oλ dense spherical microparticles is observed Figure c . This eλλect could be produced by the chanμe oλ the superλicial crystalline structure introduced by the ns nm laser pulse on the metal surλace, Fe . % in this case [ , ].

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Figure . a Fe NPs manuλactured by drawinμ lines with up to seven contiμuous pulses, b Fe NPs μenerated by percussion pulses in the same sample area . In both processes, the laser λluence was mJ/cm . “ll microμra‐ phies were obtained by SEM.

The μeneration oλ NPs in liquid media was perλormed at ambient temperature and pressure. The substrate was immersed in the liquid contained in a beaker. Laser pulses were λocused on the substrate’s surλace, while the position oλ the substrate was continuously beinμ chanμed so that each pulse would impact in a non-irradiated surλace area. Metallic NPs dispersions in diλλerent liquid media such as ultrapure H O, isopropanol, and a solution oλ sodium dodecyl sulλate SDS were obtained λollowinμ this method.

Figure . NPs μenerated in air and in diλλerent liquid media. a Tyndall eλλect in dispersions and solutions λrom leλt to riμht “μ NPs in ultrapure H O, ultrapure H O, Fe NPs in isopropanol, Fe NPs in SDS, and Fe NPs in ultrapure H O. b Characterization oλ the Fe NPs in a SDS solution by microscopy HR-TEM .

Diλλerent methods were used λor the NPs characterization

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

.

Tyndall eλλect λor a rapid veriλication oλ the NPs’ μeneration in liquid media. In order to observe this eλλect, the dispersion is illuminated with a cw laser. For example, in Fig‐ ure a, a mW cw laser @ nm was used. The presence oλ NPs disperses the laser beam and makes it visible at simple siμht. This eλλect is not observed in solutions or as in the case oλ ultrapure H O in the second beaker λrom leλt to riμht oλ Figure a.

.

Hiμh-resolution transmission electron microscopy HR-TEM , which allowed studyinμ the NPs’ appearance, λorm and size Figure b .

.

UV–visible liμht absorption spectrophotometry λor the analysis oλ suspensions.

The advantaμe oλ this last method is that it allows preservinμ the NPs’ properties in situ, avoidinμ alterations due to dryinμ eλλects. Clusterinμ or oxidation eλλects usually appear when the NPs are separated λrom the medium in which they were oriμinated Figure . Finally, the size distribution oλ the NPs in their oriμinal medium was estimated λrom the absorbance spectra oλ the dispersions and their comparison with those calculated with the MiePlot alμorithm “ppendix E, reλerence [ ] .

Figure . a “bsorbance spectrum oλ a dispersion oλ “u NPs in ultrapure H O compared to that oλ the same disper‐ sion diluted times, b comparison oλ the absorbance spectrum oλ “μ NPs in H O experimentally obtained with that calculated λor “μ NPs oλ nm oλ radius in H O with a loμ-normal distribution with diλλerent standard deviations.

2.2. . . Core–shell nanoparticles preliminary results Nanoparticles oλ diλλerent nucleus’ materials and core–shell were produced as prototypes λor drug delivery. The particles were required to have a λerromaμnetic nucleus to be able to be delivered with maμnets to the desired zones and a core–shell oλ a material assimilable by the orμanism so as not to be rejected by it. The λollowinμ method was used λor the synthesis oλ core–shell NPs. First, a suspension oλ Fe NPs in ultrapure H O was obtained by laser ablation oλ a Fe . % plate. “n “u . % plate was subsequently irradiated in the Fe NPs suspension. The Fe NPs acted as nucleation centers λor “u crystallization accordinμ to the nucleation principles described in Section . . . . The absorbance spectrum oλ the λinal suspension obtained, shown in Figure , resulted in very μood aμreement with those reported by other authors in reλerences [ , ].

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Figure

. “bsorbance spectrum oλ dispersions oλ Fe NPs, “u NPs, and Fe@“u NPs in ultrapure H O.

. Conclusions Laser ablation allows numerous technoloμical developments ranμinμ λrom laser-induced breakdown spectroscopy LI”S , pulsed laser deposition PLD , laser propulsion, to surλace modiλication and μeneration oλ nanoparticles, NPs. In this chapter, we have presented a review oλ the results obtained with these two latter processes. However, it should be noted that these eλλects or phenomena were λound to occur durinμ the implementation oλ the micromachininμ processes and have μained relevance since their observation by means oλ electron microscopy in its diλλerent λorms SEM and TEM. The possibility oλ producinμ nanostructures on surλaces opens up new possibilities λor studyinμ their eλλects on physicochemical surλace phenomena. These eλλects, mentioned in the Section . . , as laser-induced periodic surλace structures and the increase oλ rouμhness in the μeneration oλ channels λor chromatoμraphic columns will allow the production oλ cheaper systems based on these principles. On the other hand, the heuristic model presented in Section . to explain the phenomenon oλ laser ablation allows us to understand the eλλect oλ surλace modiλication and use it as a tool to transλorm surλaces by coatinμ them with thin λilms. “nother very important issue is the possibility oλ producinμ core–shell nanoparticles oλ the type shown in the Section . , usinμ diλλerent metals. In our case, the production oλ Fe@“u NPs resulted a very convenient way to uniλy in a same material the maμnetic properties oλ Fe with the bioloμical properties oλ “u. “s a λinal remark, as it was our intention to put λorward throuμhout this chapter, we would like to emphasize that nanosecond lasers are still a very important source λor the modiλication oλ surλaces λor technoloμical uses.

Nanostructuring of Material Surfaces by Laser Ablation http://dx.doi.org/10.5772/62638

Author details Cinthya Toro Salazar , María Laura “zcárate , and Carlos “lberto Rinaldi ,

, *

*“ddress all correspondence to rinaldi@cnea.μov.ar Centro de Investiμaciones en Láseres y “plicaciones CEIL“P CITEDEF-CONICET , ”uenos “ires, “rμentina Consejo Nacional de Investiμaciones Cientíλicas Técnicas, ”uenos “ires, “rμentina Comisión Nacional de Enerμía “tómica, ”uenos “ires, “rμentina Escuela de Ciencia y Tecnoloμía, UNS“M, ”uenos “ires, “rμentina

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