Monte Carlo study of molecular weight distribution changes induced by degradation of ion beam irradiated polymers

In this work we study a polymeric material that degrades upon irradiation due to the energy inhomogeneously deposited by heavy ion beams. Ion beam irradiation of polymers generates rather different effects than those induced by “classical” low ionizing particles such as electrons or gamma rays. This is due to the high electronic stopping power and the inhomogeneous distribution of deposited energy. This energy is transferred to the material within a small volume along the ion path forming the so called “nuclear track” or “latent track”. The track size primarily depends on the ion velocity, and it is determined by the secondary electrons (delta rays) generated along the ion trajectory. By means of Monte Carlo simulations we first obtained equilibrated polymer configurations using a coarse-grained model, and then investigated the spatially inhomogeneous chain scission process due to the passage of the ions. The number average molecular weight, weight average molecular weight and the polydispersity were calculated as a function of track radius, scission probability within the ion track and irradiation fluence. Finally we compared our results with a numerical implementation of a model for random homogeneous degradation.     

Effect of different ion beam energy on properties of amorphous carbon film fabricated by ion beam sputtering deposition (IBSD)

Amorphous carbon (a-C) films were fabricated by ion beam sputtering technique. The influence of sputtering ion beam energy on bonding structure, morphologic, mechanical properties, tribological properties and corrosion resistance of a-C films are investigated systematically. Morphology study shows that lowest surface roughness exists for mid-ion beam energy. Improved adhesion is observed for the films that are prepared under high ion beam energy, attributed to film graphitization, low residual stress and mixed interface. Relatively, a-C films prepared with ion beam energy of 2 keV exhibits optimum sp³ bond content, mechanical properties and corrosion resistance. It is found that the wear rate of DLC films decrease with increased ion beam energy in general, consistent with the varied trend of the H/E value which has been regarded as a suitable parameter for predicting wear resistance of the coatings. The correlation of the sp³ bond fraction in the films estimated from Raman spectroscopy with residual stress, nanohardness and corrosion resistance has been established.     

Assessment of DNA damage of Lewis lung carcinoma cells irradiated by carbon ions and X-rays using alkaline comet assay

DNA damage and cell reproductive death determined by alkaline comet and clonogenic survival assays were examined in Lewis lung carcinoma cells after exposure to 89.63 MeV/u carbon ion and 6 MV X-ray irradiations, respectively. Based on the survival data, Lewis lung carcinoma cells were verified to be more radiosensitive to the carbon ion beam than to the X-ray irradiation. The relative biological effectiveness (RBE) value, which was up to 1.77 at 10% survival level, showed that the DNA damage induced by the high-LET carbon ion beam was more remarkable than that induced by the low-LET X-ray irradiation. The dose response curves of “Tail DNA (%)” (TD) and “Olive tail moment” (OTM) for the carbon ion irradiation showed saturation beyond about 8 Gy. This behavior was not found in the X-ray curves. Additionally, the carbon ion beam produced a lower survival fraction at 2 Gy (SF2) value and a higher initial Olive tail moment 2 Gy (OTM2) than those for the X-ray irradiation. These results suggest that carbon ion beams having high-LET values produced more severe cell reproductive death and DNA damage in Lewis lung carcinoma cells in comparison with X-rays and comet assay might be an effective predictive test even combining with clonogenic assay to assess cellular radiosensitivity.     

Ion beam induced formation of nanocrystalline silicon in pulsed laser deposited SiOX thin films

Synthesis and structural studies of nanocrystalline silicon grown in pulsed laser deposited SiO_X films is reported. The effect of high energy heavy ion beam irradiation on these films is studied using 100 MeV Ag ions. The structural studies were carried out using micro Raman spectroscopy, GAXRD, FTIR, TEM, HRTEM, SAED and EDX. The occurrence of phase separation in non-stoichiometric silicon oxide by means of ion beam irradiation leading to the formation of silicon nanocrystals in the films is confirmed by the results. HRTEM results reveal the structure of silicon phase formed after ion beam treatment and the particle size can be controlled up to 2-3 nm. A detailed analysis by micro Raman and HRTEM studies suggest the presence of crystallite size distribution. The results of GAXRD and SAED confirm the formation of cubic phase of silicon with two different lattice parameters. The studies conclude that the size of the nanocrystals can be controlled by varying deposition and ion irradiation parameters.     

Structural modifications induced by swift heavy ions in thin films of yttria fully stabilized zirconia

Among ceramic materials for nuclear waste containment, single crystal yttria fully stabilized zirconia (FSZ) gained particular consideration because of its excellent radiation resistance both in the elastic and inelastic collision regime. We deposited amorphous and polycrystalline, cubic FSZ thin films on (1 0 0) Si by ultraviolet pulsed laser ablation and irradiated them with swift heavy uranium ions of 2.6-GeV energy at fluences between 2 and 12 × 10¹¹ ions cm⁻². The films were characterized before and after irradiation using X-ray reflectivity, grazing incidence X-ray diffraction, micro-Raman spectroscopy and transmission electron microscopy. Under ion irradiation, as-deposited crystalline films undergo amorphisation, followed by partial recrystallisation, whereas as-deposited amorphous films retain their disordered character. The dominant defects produced in the films are oxygen vacancies which may explain the amorphisation to recrystallisation path of our crystalline films.     

Fast neutron inspection of sea containers for the presence of “dirty bomb”

The possibility of the detection of “dirty bomb” presence inside sea containers is evaluated. The method proposed for explosive and fissile material detection makes use of two sensors (X-rays and neutrons). A commercial imaging device based on the X-ray radiography performs a fast scan of the container, identifies a “suspect” region and provides its coordinates to the neutron based device for the final “confirmatory” inspection. In this two sensor system a 14 MeV neutron beam defined by the detection of associated alpha particles is used for interrogation of only volume elements marked by X-ray sensor. The object’s nature is determined from passive and neutron induced, gamma energy spectra measurements. Experimental results (time-of-flight and gamma energy spectra) obtained for the irradiation 30 kg of TNT, depleted uranium and other materials hidden inside the container are presented.     

Effect of electron beam irradiation sterilization on the biomedical poly (octene-co-ethylene)/polypropylene films

The effect of electron beam irradiation with the dose ranging from 15 to 40 kGy on poly (octene-co-ethylene) (POE)/polypropylene (PP) films was investigated. Wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), yellowness index testing and mechanical performance measurement were applied to characterize the films. It demonstrated that crystalline structure exhibited little change, and degree of crystallinity slightly change under the irradiation treatment. Irradiation brought about oxidation of the films, forming hydroxyl groups of the peroxides and carbonyl groups. Tensile properties become worse as irradiation dose increased. Electron beam irradiation with the dose of 15-40 kGy has little effect on crystalline performance and a little influence for the POE/PP films, indicating a good irradiation resistance.     

Deposition of polycrystalline Si thin films on glass substrates by direct negative Si ion beam deposition

Polycrystalline Si (Poly-Si) thin films were deposited on a glass substrate by direct negative Si (Si⁻) ion beam deposition. The glass substrate temperature was kept constant at 500 °C for all depositions. Prior to deposition, the ion energy spread and ion-to-atom arrival ratio were evaluated as a function of the ion beam energy.The Si⁻ ion energy spread was less than 10% regardless of the ion energy, while the ion-to-atom arrival ratio increased proportionally from 1.3 to 1.6 according to the ion beam energy.Atomic force microscopy images showed that a relatively rough surface was obtained at 50 eV of Si⁻ ion energy and it is also concluded that the Si⁻ ion beam irradiation at 50 eV is effective to deposit Si thin film with small grains as shown in Fig. 3.     

Effect of SHI on dielectric and magnetic properties of metal oxide/PMMA nanocomposites

Magnetic nanoparticles embedded in polymer matrices have excellent potential for electromagnetic device applications like electromagnetic interference suppression, etc. The NiO nanoparticles were synthesized by simple method. These nanoparticles were dispersed in PMMA matrix and films were prepared by casting method with varying concentrations of nickel oxide nanoparticles. These films were irradiated with 50 MeV Li⁺³ ions at a fluence of 5 × 10¹² ions/cm². AC electrical properties of pristine and irradiated samples were studied in wide frequency range. Dependence of dielectric properties on frequency, ion beam fluence and filler concentration was studied. The results reveal the enhancement in dielectric properties after doping nanoparticles and also upon irradiation, which is also corroborated with field-cooled-zero-field-cooled (FC-ZFC) susceptibility measurement in which magnetization is increased upon irradiation. The Fourier transform infrared (FTIR) spectroscopy analysis revealed the change in the intensity of functional groups after irradiation. Average surface roughness observed to change with filler concentration and also with the irradiation fluence as obtained from AFM analysis.     

HDPE预辐照接枝SSS与AA体系的反应动力学研究

采用电子束引发预辐照接枝方法在高密度聚乙烯(HDPE)上接枝丙烯酸(AA)与对苯乙烯磺酸钠(SSS)两种单体,以制备含磺酸和羧酸基团的双功能基阳离子交换膜。研究发现,接枝速率与辐照剂量、单体总浓度及反应温度密切相关。接枝反应的活化能为22．2kJ／mol。傅立叶变换红外光谱(FTIR)测试表明,接枝膜上引入了磺酸基团和羧酸基团。     

Heavy ion beam induced phenomena in polytetrafluoroethylene

This paper describes the results on thermal and chemical analysis of polytetrafluoroethylene (PTFE) film stack after high-energy heavy ion beam irradiation under atmospheric fields at room temperature. After high-energy C⁶⁺ ion beam irradiation, the PTFE film stack was separated one by one, and then the various measurements such as differential scanning calorimetric (DSC) analysis and solid-state ¹⁹F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy were performed to get information of the chemical reaction and structural change at the localized positions. By ion beam irradiation for PTFE at room temperature, it is suggested that the abnormal phenomena due to the change of morphology could be observed by DSC analysis. In the solid-state ¹⁹F-MAS-NMR spectroscopy of ion irradiated PTFE film including Bragg peak region, several new signals were observed besides the intense peak of -CF₂- at −124 ppm. The detected new signals in ion irradiated PTFE should be due to the changed chemical structures. The signals, which are assigned, to the tertiary carbon group with branching site (Y-type crosslinking site), perfluoro-propylene site and chain end methyl site were directly detected, though it was under the oxidation condition. Thus, although it was under the oxidation condition, the branching or crosslinking reaction was taken place with the chain scission in the matrix. Moreover, the branched chain length would become short, compared with EB-crosslinked PTFE. Hence, it could be suggested that the irradiation of heavy ion beam induced large amounts of intermediate species, compared with EB or γ-ray irradiation, and then, those would be reacted with each other in the localized area. Especially, in region of the Bragg peak, the ion beam induced more large amounts of intermediate species than in the other region.     

Formation of Nano-Crystalline Phase in Hydrogenated Amorphous Silicon Thin Film by Plasma Focus Ion Beam Irradiation

A 3.3 kJ Mather type dense plasma focus device is used to generate a pulsed argon ion beam of 100 KeV in this work. Hydrogenated amorphous silicon (a-Si:H) film prepared by plasma enhanced chemical vapor deposition (PECVD) on c-Si substrate was irradiated with the argon ion beam produced by this dense plasma focus device. The effects of exposure to a single, 5 and 10 shots of dense plasma focus argon ion beam irradiation on the surface morphology, crystallinity and chemical bonding properties of the a-Si:H films were studied using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD), Raman scattering and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Formation of nano-crystalline silicon phase along with increase in structural order and hydrogen content in the film structure has been observed when the a-Si:H film was irradiated with a single shot of dense plasma focus argon ion beam. Exposure to 5 and 10 shots of the dense plasma focus argon ion beam irradiation reduced the hydrogen content resulting in a decrease in crystallinity and structural order in the film structure.     

Positron annihilation lifetime and Doppler broadening study in 50 MeV Li3+ ion irradiated polystyrene films

Swift heavy ion (SHI) irradiation of polymeric materials results in the change of their free volume properties which have strong correlation with their macroscopic properties. The modification depends on the polymer and ion beam parameters, namely ion energy, fluence and ion species. Polystyrene films were irradiated with Li³⁺ ions of energy 50 MeV from 15 UD Pelletron accelerators at Inter University Accelerator Centre (IUAC), New Delhi, India to the fluences of 10¹¹, 10¹² and 10¹³ ions/cm². Nanosized free volume parameters in the polymer have been studied by positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS). From o-Ps lifetime τ_3, free volume hole radius, mean free volume of microvoids and fractional free volume are computed and modification in free volume with the fluence is studied. Free volume parameters change slowly with ion fluence with a decrease at the highest fluence of 10¹³ ions/cm². The decrease in τ₃ and I₃ (reflecting the number of free volume holes) may be interpreted on the process of cross-linking. S parameter obtained from DBS measurements showed a minor decrease with increasing fluence.     

The selection and characterization of the mutants in bioflocculant bacteria C8 induced by 3 MeV helium ion irradiation

A 3 MeV He²⁺ beam was used to irradiate C8 (a flocculant-producing bacteria) with a fluence ranging from 10¹¹ to 10¹³ ions/cm². The effects on the survival ratio, TTC-dehydrogenase activity, flocculating activity and RAPD analysis are reported. The survival ratio curve caused by irradiation is proved to be “saddle-shaped”. Eleven mutants were obtained, all of which had a significant change in dehydrogenase activity and most showed a positive change in flocculating activity. RAPD measurements were used to analyse the DNA of mutants with a flocculating activity over 80%, which indicated that all their DNA had been changed by irradiation.     

离子束辅助沉积立方氮化硼的试验研究

运用离子束辅助沉积(IBAD)法在硅片上制备了立方氮化硼(c—BN)薄膜，研究了辅助能量、辅助束流及辅助束中氮气含量等参数对膜中c—BN含量的影响。用红外光谱(FTIR)及X射线光电子能谱(XPS)分析技术对得到的c—BN膜进行了分析。结果表明：合适的离子辅助能量能够获得c—BN含量高的薄膜；膜中c—BN的含量随辅助气体中N2含量的提高而增加；辅助束流对薄膜的形成影响不明显。     

Software for automatization of IEA-analysis of plasma-laser spectra

A software has been developed in order to automatize the ion energy analyzer (IEA) spectra analysis of laser-generated plasmas.A Nd:Yag laser operating at an intensity of the order of 10¹⁰ W/cm², 9 ns pulse width and energy of the order of 600 mJ, has been employed to irradiate different metallic targets (Al, Ti, W) and to produce plasma pulses. The ion emission from the plasma is monitored through an IEA instrument permitting time-of-flight (TOF) measurements to determine the ion energy distributions as a function of the charge state.The software program consists in two sections. The first one permits to identify the IEA ion peaks corresponding to different charge states as a function of the theoretical TOF values. The second section permits to plot the ion velocity and energy distributions as a function of the charge state. The obtained distributions are fitted using the “Coulomb-Boltzamnn shifted” function approach through the “Peakfit” code. The fit of the experimental data permits to estimate the equivalent plasma temperature and the average energy shift of the distributions as a function of the ion charge state.     

Development of sulfonated FEP-Nafion hybrid proton exchange membranes for PEFC

The performance of polymer electrolyte fuel cell (PEFC) is affected by an interfacial property between a proton exchange membrane (PEM) and electrodes. Thus, to develop a well-laminated membrane electrode assembly (MEA), a hybrid PEM (FN) was fabricated by mixing a radiation grafted membrane (sulfonated FEP) with ionomer (Nafion^® dispersion) which is applied to coat the interface of the PEM and electrodes.The obtained FN, sulfonated FEP and Nafion^®112 were characterized in terms of water uptake, ion exchange capacity (IEC), polarization performance and electrochemical impedance. FN showed high IEC and water uptake, which would induce the highest ionic conductivity (IC) among tested PEMs. In terms of FN, the interface between the PEM and electrodes should have been improved because FN showed the lowest charge transfer resistance than other tested PEMs. The high IC and improved interface between the PEM and electrodes resulted in the best cell performance of FN in tested PEMs.     

Structural characteristics of rutile films prepared by direct deposition and neon ion beam assisted deposition

In this article, titanium dioxide films prepared by neon ion beam assisted deposition (IBAD) in an oxygen environment were investigated. The deposition rate was varied from 0.2 to 0.4 nm/s while the current density and ion energy were kept at 20 μA/cm² and 40 keV. The structural characteristics of all films were studied by X-ray diffraction and Raman spectroscopy. Results show that all the films exhibit a rutile phase. The location of (2 0 0) diffraction peaks deviated from the standard value. Simultaneously, the relative intensity of (2 0 0)/(1 1 0) peaks decreases with increasing evaporation rate. All results are discussed in terms of surface free energy and ion channeling effects.     

Structural and optical study of irradiation effect in GaN epilayers induced by 308 MeV Xe ions

Wurtzite GaN epilayers irradiated at room temperature with 308 MeV ¹²⁹Xe³⁵⁺ ions to fluences of 1 × 10¹³ and 3 × 10¹³ cm⁻² have been studied by contact mode atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), micro-Raman scattering and photoluminescence (PL) spectroscopy. The AFM images showed that the surface of GaN films was etched efficiently due to the Xe ion irradiation. The initial step-terrace structure on GaN surface was eliminated completely at a fluence of 3 × 10¹³ cm⁻². HRXRD and Raman results indicated that the Xe ion irradiation led to a homogenous lattice expansion throughout the entire ∼3 μm-thick GaN films. The lattice expansion as well as the biaxial compressive stress of the films was increasing with the increase of ion fluence. PL measurements showed that a dominant yellow luminescence band in the as-grown GaN films disappeared, but a blue and a green luminescence bands were produced after irradiation. Based on these results, the strong electronic excitation effect of 308 MeV Xe ions in GaN is discussed.     

Low temperature resistivity study of nanostructured polypyrrole films under electronic excitations

The synthesis of nanostructured polypyrrole (Ppy) films by electrochemical process and their modifications by electronic excitations induced by swift heavy ion irradiations is reported in this paper. The electrical property of ion beam irradiated polypyrrole was investigated at low temperature by resistivity measurements. The structural and optical properties were also studied using X-ray diffraction (XRD), UV-vis spectroscopy and scanning electron microscopy (SEM). At low temperature, the polypyrrole films show the metallic behaviour after ion beam irradiation. UV-vis spectroscopy shows a red shift in the absorbance edge and thus reduction in band gap with increasing ion fluence. The structural studies show that the percentage crystallinity improves with increase in ion fluence. The SEM study corroborates the results of structural analysis and shows the formation of rod type structures along with the evolution of amorphous phase with increasing ion fluence.