This work reports on damage production in polymers by high-energy ions within the framework of the inelastic thermal spike model (i-TS). The model is used to describe the effective size of the damaged region around the ion path (the track size) in amorphous poly(methyl methacrylate) (PMMA) and the semicrystalline poly(p-phenylene sulphide) (PPS), poly(ethylene terephthalate) (PET), and poly(vinylidene difluoride) (PVDF). Track size calculations are compared to experimental data deduced from measurements of crater size, bond-breaking cross-sections, changes in crystallinity and electron density, track etching, and electrical depolarization. The use of data obtained from distinct types of damage provides a broad platform to test the applicability of the model to polymers. This work shows that the i-TS correctly describes the dependence of the track size on energy loss obtained from most experimental probes, when the activation energy of thermal decomposition of the polymers is used as the criterion of track formation, using an electron-phonon mean free path of approximate to 3 nm. As damage is not uniform across the ion track radial dimension, there are fine variations in the experimental damage radii that can only be accounted for by using multiple activation processes. Amorphization radii of the semicrystalline polymers are not directly correlated to melting induced by the ions.

The material exposed to energetic radiation may change its properties and performance. Ion beam irradiation is an established method to investigate radiation damage in materials. In the present study, SRIM code is employed as a tool to determine the electronic and nuclear energy losses and displacement per atom (DPA) associated with the damage induced in Al2O3 using 100 MeV Au ion. We have further studied the creation of 100 MeV Au ion induced molten zone along the ion track in Al2O3 in the framework of the thermal spike (TS) model. Using the in-elastic thermal spike model, elastic thermal spike model, and unified thermal spike model, the evolution of lattice temperature and latent track radius as a function of depth of Al2O3 for 100 MeV Au ion irradiation are investigated. The current results demonstrate that the latent track radius shows a U-shaped variation based on the combined effect of electronic stopping power and nuclear stopping power. In order to corroborate these results, an additional irradiation experiment was performed using swift heavy ion (SHI), 100 MeV Au ions with fluence 1×1014 ions/cm2 for Al2O3. To investigate the structural properties, surface morphology and to identify the defects in the samples, pristine and irradiated Al2O3 samples were characterized by Grazing Incident X-Ray Diffraction (GIXRD), Atomic Force Microscopy (AFM) and Photoluminescence Spectroscopy (PL). AFM study shows the increase in roughness after SHI irradiation. A decrease in intensity of PL spectra upon SHI irradiation indicates the formation of new defects and disordered structures in the material, which is quite in agreement with the theoretical results.

Damaged regions of cylindrical shapes called ion tracks, typically in nano-meters wide and tens micro-meters long, are formed along the ion trajectories in many insulators, when high energy ions in the electronic stopping regime are injected. In most cases, the ion tracks were assumed as consequences of dense electronic energy deposition from the high energy ions, except some cases where the synergy effect with the nuclear energy deposition plays an important role. In crystalline Si (c-Si), no tracks have been observed with any monomer ions up to GeV. Tracks are formed in c-Si under 40 MeV fullerene (C60) cluster ion irradiation, which provides much higher energy deposition than monomer ions. The track diameter decreases with decreasing the ion energy until they disappear at an extrapolated value of ~ 17 MeV. However, here we report the track formation of 10 nm in diameter under C60 ion irradiation of 6 MeV, i.e., much lower than the extrapolated threshold. The diameters of 10 nm were comparable to those under 40 MeV C60 irradiation. Furthermore, the tracks formed by 6 MeV C60 irradiation consisted of damaged crystalline, while those formed by 40 MeV C60 irradiation were amorphous. The track formation was observed down to 1 MeV and probably lower with decreasing the track diameters. The track lengths were much shorter than those expected from the drop of Se below the threshold. These track formations at such low energies cannot be explained by the conventional purely electronic energy deposition mechanism, indicating another origin, e.g., the synergy effect between the electronic and nuclear energy depositions, or dual transitions of transient melting and boiling.

Material sputtered from CaF2 single crystals by 180 MeV Au ions impinging at different incidence angles were collected on high-purity amorphous C-coated Cu grids and Si100 wafer catcher surfaces over a broad angular range. These catcher surfaces were characterized complementary by transmission electron microscopy, atomic force microscopy and medium energy ion scattering, revealing the presence of a distribution of partially buried CaF2 nanoparticles in conjunction to a thin layer of deposited CaF2 material. Particle size distributions do not follow simple power laws and depend on the angles of ion incidence and particle detection. It is shown that the particle ejection is directly related to the jet-like component of sputtering, previously observed in ionic crystals, contributing significantly to the total yield. This contribution enhances as the impinging ions approach grazing incidence. Possible scenarios for the emission of particles are discussed in light of these observations.

Boron carbide (B4C) behavior under irradiation is widely studied in order to predict the lifetime of this material in future (Generation IV) nuclear fission reactors. This paper is focused on the effects of high electronic stopping powers (Se) on B4C structure modifications. Sintered B4C samples were irradiated at room temperature with swif(t) heavy ions (between 0.5 and 3 MeV.u(- 1)) corresponding to Se values in the 4.1 to 15.4 keV.nm(-1) range at the sample surface. In order to investigate the structural changes as a function of depth, transmission electron microscopy and Raman mapping were performed on the irradiated samples along the path of the incident ions. For the highest Se values, damage results in the creation of large hillocks at the sample surface along with the amorphization of the bulk. These results are explained, in the frame of the inelastic thermal spike model, by local melting in latent tracks that are created only when irradiations are performed above a Se threshold evaluated at around 9 keV nm(-1). (C) 2020 Elsevier B.V. All rights reserved.

High electronic excitations in radiation of metallic targets with swift heavy ion beams at the coulomb barrier play a dominant role in the damaging processes of some metals. The inelastic thermal spike model was developed to describe tracks in materials and is applied in this paper to some systems beams/targets employed recently in some nuclear physics experiments. Taking into account the experimental conditions and the approved electron-phonon coupling factors, the results of the calculation enable to interpret the observation of the fast deformation of some targets.

Microcrystalline CeO2, ThO2, and UO2 were irradiated with 198 MeV Xe-132 ions to the same fluence at temperatures ranging from 25 degrees C to 700 degrees C then characterized by synchrotron X-ray diffraction and X-ray absorption spectroscopy. All samples retain crystallinity and their nominal fluorite-type phase at a fluence of 1.5 x 10(13) ions/cm(2). Both CeO2 and ThO2 display defect-induced unit cell expansion after irradiation at room temperature (similar to 0.15% and similar to 0.10%, respectively), yet as irradiation temperature increases, the maximum swelling produced decreases to similar to 0.02%. Alternatively, UO2 shows an initial contraction in unit cell parameter (approximately -0.05%) for room temperature irradiation, most likely related to irradiation-enhanced annealing or irradiation-induced oxidation. At higher temperatures (above 200 degrees C) UO2 begins to swell, surpassing its unit cell parameter prior to irradiation (similar to 0.05%), an effect which could be attributed to minor reduction in uranium oxidation state in vacuum. However, while CeO2 irradiated at room temperature undergoes partial reduction, both UO2 and ThO2 exhibit no measurable change in cation oxidation state as evidenced by X-ray absorption spectroscopy. All samples display a decrease in irradiation-induced heterogeneous microstrain as a function of increasing irradiation temperature. (C) 2019 Elsevier B.V. All rights reserved.

The sensitivity of materials towards swift heavy ion (SHI) irradiation, as determined by the widely accepted inelastic thermal spike (i-TS) model, has been found to be inaccurate in certain cases where predictably insensitive materials show SHI induced mixing (SHI mixing) across their interfaces. Conventionally, creation of SHI induced transient molten zones, not predictable in SHI insensitive materials, is largely believed to be the essential prerequisite for observing SHI mixing. In this work, prospects of 100 MeV Au ion induced mixing across Pd/Si and Ni/Si interfaces have been explored by examining whether molten state can be achieved according to the i-TS model calculations. Possibilities of melting in bulk Pd and Ni, and in the vicinity of Pd (20 nm)/Si and Ni (20 nm)/Si interfaces, have been investigated. The results indicate that although bulk Pd and Ni are SHI insensitive, melting is possible on both the sides of both the interfaces, and hence SHI mixing could occur in these two systems.

Gold and platinum nanoparticles of few-nm size were deposited on amorphous silicon nitride (a-SiN) films. These samples were irradiated with 380 MeV Au ions at grazing incident angles (theta(i) = 2 degrees-5 degrees) to a fluence of similar to 1 x 10(10) ions/cm(2). The irradiated samples were observed using transmission electron microscopy (TEM). Ion tracks were clearly observed as long bright lines. Nanoparticles were found to be desorbed from long and narrow regions along the ion tracks. The surface temperature at the thermal spike produced by the ion impact was evaluated from the observed nanoparticle desorption. The observed temperature distribution is qualitatively explained by a one-dimensional two temperature model (1D-TTM) although there are some discrepancies which may be attributed to the surface effects which are not taken into account in 1D-TTM.

Stable C-C bonds existing in several sp hybridizations place carbon thin films of different structural compositions among the materials most tolerant to radiation damage, for applications in extreme environments. One of such applications, solid state electron stripper foils for heavy-ion accelerators, requires the understanding of the structural changes induced by high-energy ion irradiation. Tolerance of carbon structure to radiation damage, thermal effects and stress waves due to swift heavy ion impacts defines the lifetime and operational efficiency of the foils. In this work, we analyze the consequences of a single swift heavy ion impact on two different amorphous carbon structures by means of molecular dynamic simulations. The structures are constructed by using two different recipes to exclude the correlation of the evolution of sp2-to-sp3 hybridization with the initial condition. Both initial structures contain approximately 60% of sp2-bonded carbon atoms, however, with different degree of clustering of atoms with sp3 hybridization. We simulate the swift heavy ion impact employing an instantaneous inelastic thermal spike model. The analysis of changes in density, bonding content and the number and size of carbon primitive rings reveals graphitization of the material within the ion track, with higher degree of disorder in the core and more order in the outer shell. Simulated track dimensions are comparable to those observed in small angle x-ray scattering measurements of evaporation-deposited amorphous carbon stripper foils irradiated by 1.14 GeV U ions.

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The damage induced in cerium dioxide by swift heavy ion irradiation was studied by micro-Raman spectroscopy. For this purpose, polycrystalline sintered pellets were irradiated by 100-MeV Kr, 200-MeV Xe, 10-MeV, and 36-MeV W ions in a wide range of fluence and stopping power (up to ∼28 MeV μm−1). No amorphization of ceria was found whatsoever, as shown by the presence of the peak of Raman-active T2g mode (centered at 467 cm−1) of the cubic fluorite structure for all irradiation conditions. However, a clear decrease of the T2g mode peak intensity was observed as a function of ion fluence to an asymptotic relative value of about 45%. Similar decays were also observed for satellite peaks and second-order peaks. Track radii deduced from the decay kinetics for the 36-MeV W ion data are in good agreement with previous determinations by X-ray diffraction and reproduced by the inelastic thermal spike model for low ion velocities. However, interaction between the nuclear and electronic stopping powers is needed to describe the decay kinetics of 10-MeV W ion data by the thermal spike process. Moreover, the asymmetrical broadening of the main T2g peak after irradiation was analyzed with different theoretical models.

Gold and platinum nanoparticles of few-nm size were deposited on amorphous silicon oxide and amorphous silicon nitride films. These films were irradiated with 0.72 and 1.1MeV C603+ ions. Local heating of these films induced by the single ion impact was evaluated by observing desorption of the nanoparticles from the target surfaces upon ion impact. It was found that the local heating at the exit surface is very sensitive to the film thickness. For thinner films, the observed local heating at the exit surface is enhanced compared to the entrance surface while the result is opposite for thicker films. The observed result can be well explained by the unified thermal spike model taking account of the broadening of the spatial distribution of constituent carbon ions during the passage across the film.

Simple and complex borosilicate glasses were irradiated with single and double ion beams of light and heavy ions over a broad fluence and stopping power range. As a result of the heavy ion irradiation (U, Kr, Au), the hardness was observed to diminish and saturate after a decrease by 35 +/- 1%. Unlike slow and swift heavy ion irradiation, irradiation with light ions (He,O) induced a saturation hardness decrease of 18 1% only. During double ion beam irradiation; where glasses were first irradiated with a heavy ion (gold) and then by a light ion (helium), the light ion irradiation induced partial damage recovery. As a consequence of the recovery effect, the hardness of the pre-irradiated glasses increased by 10-15% depending on the chemical composition. These results highlight that the nuclear energy loss and high electronic energy loss (>= 4 keV/nm) result in significant and similar modifications whereas light ions with low electronic energy loss (<= 1 keV/nm) result in only mild damage formation in virgin glasses and recovery in highly pre-damaged glasses. These results are important to understand the damage formation and recovery in actinide bearing minerals and in glasses subjected to self-irradiation by alpha decays. (C) 2015 Elsevier B.V. All rights reserved.

Few-nm sized gold, platinum and palladium nanoparticles were deposited on amorphous silicon nitride films. These films were irradiated with 420MeV Au and 100MeV Xe ions. Temperature distributions of thermal spikes produced by these ions were evaluated by observing desorption of the nanoparticles from the target surfaces upon ion impact. It was found that the temperature of the thermal spike produced by 420MeV Au is higher than 100MeV Xe. The observed temperature of the thermal spike at the entrance surface is slightly lower than that at the exit surface both for 420MeV Au and 100MeV Xe ions. These results can be well explained by the inelastic thermal spike model.

Pronounced swelling is observed when single crystals of yttrium iron garnet Y3Fe5O12 (YIG) are irradiated in the electronic energy loss regime with various swift heavy ions. The out-of-plane swelling was measured by scanning across the border line between an irradiated and a virgin area of the sample surface with the tip of a profilometer. The step height varied between 20 and 600nm depending on fluence, electronic energy loss and total range of the ions. The step height divided by the ion range as a function of the ion fluence exhibits a linear increase in the initial phase and saturates at high fluences leading to a density decrease of around 1.7%. With complementary channeling-Rutherford-backscattering experiments (c-RBS), the damage fraction and the corresponding damage cross section were extracted and compared to the cross section deduced from swelling measurements. Irradiation effects were also characterized by scanning force microscopy (SFM). A threshold for damage creation as deduced from all the present physical characterizations is 5.5±1.0keV/nm. The value is in full agreement with previous measurements confirming that swelling and SFM characterizations can provide information concerning the electronic energy loss threshold for track formation. In contrast, track radii deduced from swelling measurements are smaller and radii from SFM are larger than deduced from c-RBS analysis. The results of Y3Fe5O12 of this work are compared with data obtained for other crystalline oxides and for ionic crystals.

The different models developed to describe track formation induced by swift heavy ions will be presented. The macroscopic ones are the Coulomb explosion model, the bond weakening (BW) model, the exciton self-trapping (STX) model, the concept of reduced electronic energy loss, the analytical thermal spike model, the IDEA (Ionization Diffusion-Explosion-Amorphization) model, the inelastic thermal spike model (i-TS) and to finish microscopic descriptions using molecular dynamic (MD) calculations. All the models were applied to describe the track formation in different kinds of materials (metals, semiconductors or insulators), while additionally the i-TS model and MD calculations were used to describe the sputtering yield. It will be shown that the initial energy deposition plays an important role in the different descriptions and that there is no simple link between the energy deposited in the electronic and later in the atomic system. The large number of models presented here shows by itself that we are far away from a complete description of track formation. So the ambition here is just to give a present status of the different models.

A number of studies have suggested that the irradiation behavior and damage processes occurring during sequential and simultaneous particle irradiations can significantly differ. Currently, there is no definite answer as to why and when such differences are seen. Additionally, the conventional multi-particle irradiation facilities cannot correctly reproduce the complex irradiation scenarios experienced in a number of environments like space and nuclear reactors. Therefore, a better understanding of multi-particle irradiation problems and possible alternatives are needed. This study shows ionization induced thermal spike and defect recovery during sequential and simultaneous ion irradiation of amorphous silica. The simultaneous irradiation scenario is shown to be equivalent to multiple small sequential irradiation scenarios containing latent damage formation and recovery mechanisms. The results highlight the absence of any new damage mechanism and time-space correlation between various damage events during simultaneous irradiation of amorphous silica. This offers a new and convenient way to simulate and understand complex multi-particle irradiation problems.

Gold and platinum nanoparticles of few-nm size were deposited on amorphous silicon nitride (a-SiN) films. These samples were irradiated with 1.1MeV C603+ ions to a fluence of ∼5×1010ions/cm2 and observed using transmission electron microscopy (TEM). The ion tracks were clearly seen as bright spots and the metal nanoparticles disappeared from a neighboring region (5–10nm) around each ion track. The platinum-nanoparticle-cleared region is slightly smaller than that of gold nanoparticles. This trend can be reproduced by the u-TS calculations assuming that the nanoparticles are desorbed when the local temperature surpasses the melting point of nanoparticles as was predicted by molecular dynamics simulations (Anders et al., 2009). This indicates that the temperature distribution in a nanometer region can be evaluated by observing the desorption of nanoparticles of different metals having different melting temperatures.