Thermal Spike Research Articles

Molecular dynamics simulation of effects of Al on the evolution of displacement cascades in AlxCoCrFeNi high entropy alloys

This work studied the evolution of displacement cascades in AlxCoCrFeNi high entropy alloys (HEAs) with different Al contents by molecular dynamics (MD) simulation to reveal the effects of Al and its-induced microstructural variations on the primary structure damage of HEAs exposed to energetic particle irradiations. Both the amount of peak Frenkel pairs and recombination efficiency of Frenkel pairs in the displacement cascades are increased with Al content, which are induced by the decrease of atomic displacement energies and prolonged thermal spike, respectively. The amount of surviving defects depends on the competition between the two effects. When the PKA energies are 5 and 10 keV, both effects are comparable, resulting in that the amount of surviving defects first decreases and then increases with Al content. The minimum amount of surviving defects is present for Al content of 5 at. %. When the PKA energy is further increased to 20 keV, the increase of peak Frenkel pairs becomes dominant, resulting in the amount of surviving defects increases monotonically with Al content. Moreover, the vacancy clustering is restrained but the interstitial clustering is promoted with increasing Al content. The current results indicate that the addition of oversized alloying elements could introduce two opposite effects in the primary damage stage of HEAs, which should be considered in the design of novel HEAs with higher irradiation resistances.

Simulation of the Irradiation Cascade Effect of 6H-SiC Based on Molecular Dynamics Principles.

When semiconductor materials are exposed to radiation fields, cascade collision effects may form between the radiation particles in the radiation field and the lattice atoms in the target material, creating irradiation defects that can lead to degradation or failure of the performance of the device. In fact, 6H-SiC is one of the typical materials for third-generation broadband semiconductors and has been widely used in many areas of intense radiation, such as deep space exploration. In this paper, the irradiation cascade effect between irradiated particles of different energies in the radiation and lattice atoms in 6H-SiC target materials is simulated based on the molecular dynamics analysis method, and images of the microscopic trajectory evolution of PKA and SKA are obtained. The recombination rates of the Frenkel pairs were calculated at PKA energies of 1 keV, 2 keV, 5 keV, and 10 keV. The relationship between the number of defects, the spatial distribution pattern of defects, and the clustering of defects in the irradiation cascade effect of 6H-SiC materials with time and the energy of PKA are investigated. The results show that the clusters are dominated by vacant clusters and are mainly distributed near the trajectories of the SKA. The number and size of vacant clusters, the number of Frenkel pairs, and the intensity of cascade collisions of SKAs are positively correlated with the magnitude of the energy of the PKA. The recombination rate of Frenkel pairs is negatively correlated with the magnitude of the energy of PKA.

Early cataloguing of fragments from break-up events

Break-up events represent the dominant source of objects in space catalogues, surpassing half of the overall population. These not so uncommon events include explosions, collisions or anomalous events resulting in fragmentations and their number is estimated to be higher than 630. The early cataloguing of the fragments generated during these events poses a complex challenge for space objects catalogue build-up and maintenance processes. The provision of Space Surveillance and Tracking products and services during the few first days after a break-up event can be crucial to avoid collisions between the fragments and other space objects, particularly in highly congested regimes, such as Low Earth Orbit. In this regard, reducing the time required to accurately estimate the trajectories of the fragments may enable the execution of collision avoidance manoeuvres, in the case of operational space objects with manoeuvre capabilities, and analyse potential collision cascade events, which may endanger the space environment. This paper studies the whole cataloguing process after a break-up event, starting from a catalogue with no fragments from the fragmentation under-analysis, and until a well-established orbit is obtained for all fragments, using a ground-based sensor network. First, the observations enter a multi-sensor multi-target track-to-track association algorithm in charge of grouping observations belonging to the same objects. To resolve the ambiguity, particularly shortly after the event, hypotheses about tracks belonging to the same fragment are generated, scored, pruned, and promoted, only when there is enough confidence, leading to the initialisation of new objects in the catalogue. As soon as the catalogue is populated, a track-to-orbit correlation algorithm is responsible for the correlation of observations and already catalogued orbits. This alleviates the track-to-track association and enables the update of the orbital estimates, required for maintaining the catalogue.

Quantifying defect production in solids at finite temperatures: Thermally-activated correlated defect recombination corrections to DPA (CRC-DPA)

It has long been recognized from low-temperature defect production experiments and molecular dynamics (MD) simulations of displacement events in metals that the surviving defect fraction relative to the calculated Norgett-Robinson Torrens (NRT) displacements per atom (dpa) ranges from ∼1 for near-threshold displacements (representative of electron irradiation) to ∼0.3 for energetic displacement cascades (relevant for fast neutrons or energetic heavy ion irradiations). This correlated point defect recombination that occurs within a few picoseconds following the creation of a primary knock-on atom (PKA) has recently been formalized in the athermal recombination corrected dpa (ARC-DPA) parameter. However, at elevated temperatures additional thermally-stimulated correlated defect recombination processes need to be considered. For example, at irradiation temperatures above defect recovery Stage I (typically ∼40–100 K for most metals), mobile self-interstitial atoms induce additional thermally-activated correlated defect recombination that can amount to 70–80% reduction in the surviving defect fraction for low PKA energies and ∼20 to 30% reduction for high PKA energies. Since most nuclear material applications involve operation above room temperature, it is generally important to include this additional correlated defect recombination in radiation effects models. Published experimental defect recovery and defect production studies on 26 metals are analyzed to extract the surviving defect fraction following thermally-activated correlated recombination as a function of PKA energy. These experimental estimates of the athermal- plus thermal-activated correlated recombination-corrected DPA (CRC-DPA) are compared with new long-term MD simulation results on Cu and Fe. The analysis indicates the CRC-DPA fraction of surviving defects in most elements for irradiation at temperatures where interstitials are mobile is ∼25% of the NRT DPA over a wide range of PKA energies relevant for electron, ion and fast neutron irradiation conditions. Limited experimental and kinetic Monte Carlo studies suggest a further reduction to ∼10% of the NRT DPA over a wide range of PKA energies when correlated recombination due to thermally activated vacancy migration is considered. This temperature-dependent CRC-DPA should be used as the defect production parameter (rather than NRT DPA or ARC-DPA) for materials irradiated at all temperatures where defects are mobile.

Defective Graphene Effects on Primary Displacement Damage and He Diffusion at a Ni–Graphene Interface: Molecular Dynamics Simulations

Ni–graphene nanocomposites with high-density interfaces have enormous potential as irradiation-tolerant materials applied in Gen-IV reactors. Nevertheless, the mechanism wherein the intrinsic and/or irradiation-induced defects of graphene affect the irradiation tolerance of the composites remains poorly understood. Here, we investigate the effects of the two types of defective graphene on the displacement damage and He diffusion of the composites, respectively, using atomistic simulations. The introduction of the intrinsic defects of graphene has a significant effect on the Ni lattice structure near the Ni–graphene interface, especially showing that after displacement cascades, the number of defects gradually increases with the increase in graphene-defective size due to the formation and growth of stacking fault tetrahedra. The existence of the irradiation-induced defects of graphene does not diminish the ability of the interface to trap He atoms/clusters and even may be maintained or improved, mainly reflected in the fact that many isolated He atoms and small clusters can gradually migrate toward the interface and the fraction of He within the interface is up to 37.72% after 1 ns. This study provides an important insight into the understanding of the association relationships of defective graphene with the irradiation tolerance of composites.

The interactions between dislocations and displacement cascades in FeCoCrNi concentrated solid-solution alloy and pure Ni

Concentrated solid-solution alloys (CSAs) have been proposed as structural materials for advanced nuclear reactors due to their great irradiation tolerance. We studied and compared the interaction processes of displacement cascades and edge dislocations in FeCoCrNi CSA and pure Ni by molecular dynamics to explore the influence of dislocations on the irradiation resistances of CSAs. The edge dislocations preferentially absorb interstitials in both materials, however, the differences between the numbers of absorbed interstitials and vacancies in FeCoCrNi are smaller than in Ni, which is attributed to the smaller difference of mobilities of interstitials and vacancies in FeCoCrNi. When the centers of displacement cascades coincide with edge dislocations, the numbers of absorbed interstitials and vacancies in edge dislocations of FeCoCrNi are essentially the same, which is independent with PKA energies. The amounts of survived interstitials and vacancies in the matrix of FeCoCrNi are closer than that in pure Ni, which would avoid the formation of numerous large vacancy clusters induced by excessive vacancies. Furthermore, the edge dislocations are enriched with Ni, Co and depleted with Fe, Cr after interactions with displacement cascades, which is consistent with experimental results. The molecular dynamics simulation results of current study reveal that the edge dislocations in CSAs can probably serve as weak biased sinks for the annihilation of irradiation-induced defects and enhancing the irradiation resistances of CSAs.

Microstructural evolution of Ti2ZrHfV0.5Mo0.2 refractory multi-principal alloy under low-energy, high-flux He ion irradiation

The irradiation response of refractory multi-principal element alloys (RMPEAs) has gained increasing attention for the potential applications in future fusion devices. In controlled fusion reactors, plasma-facing materials have to suffer continuous low-energy high flux helium (He) ion irradiations. During high flux He irradiation, vacancy-interstitial pairs can be generated through trap mutation mechanism even without cascade collision. To simplify the model, Ti2ZrHfV0.5Mo0.2 RMPEA was irradiated with 50 eV He+ (less than the minimum He displacement energy of the alloy EdTi = 67 eV) under 1200 K to various fluences of 5 × 1024 - 1 × 1026 ions/m2, and the microstructural evolution was investigated. In the irradiated RMPEA, the intense sputtering of Ti, the growth and degradation of fuzz mainly composed of Zr, Hf elements on the surface, as well as the formation of V, Mo enriched band and high density large He cavities in the subsurface layer were observed. Although the sputtering threshold energy for He of V is similar to that of Ti (ETi = 24 eV, EV = 29 eV), V showed anomalous enrichment in the subsurface layer. Moreover, unlike the W fuzz growth process, the adatoms used to form fuzz in Ti2ZrHfV0.5Mo0.2 were derived from the Zr, Hf atoms diffusing through the vacancy-solute exchange mechanism, rather than from the atoms formed by the loop-punching mechanism. The anomalous enrichment of V atoms and the different fuzz growth mechanism were attributed to (i) different migration rates for different species of atoms in the alloy under vacancy diffusion mechanism and (ii) the formation of AB2 (A = Ti, Zr, Hf; B = V, Mo) phase blocking the continued formation of prismatic dislocation loops mainly composed of V and Mo.

Effect of nanovoids on the displacement cascades and mechanical properties in INCOLOY-800H: A molecular dynamics study

Effect of nanovoids on the displacement cascades and mechanical properties in INCOLOY-800H: A molecular dynamics study

Lattice distortion and re-distortion affecting irradiation tolerance in high entropy alloys.

High entropy alloys (HEAs) are promising nuclear structural materials due to their excellent irradiation resistance. However, the essential mechanisms of irradiation tolerance in HEAs remain largely inferential and imperfectly understood. This study investigates the evolution of irradiation-induced nano-scale microstructures in Ni, FeNiCr, FeNiCrCoCu and FeNiCrCuAl HEA models by molecular dynamics simulations to elucidate the conundrums. As fewer irradiation-induced Frenkel pair (FP) residuals were found in the FeNiCrCuAl HEA model in comparison with other models, a high resistance of the HEAs to the generation of permanent defects was indicated, while also the associated relatively long thermal spike and slow recrystallization stimulated a high efficiency for the recombination/annihilation of FPs to underscore a superior structural recovery of the HEAs. Under the influence of compositional increases of constituent elements, the effect of severe lattice distortion by energetics modifications was found to stimulate decreased atomic mobility accompanied by inhibited dislocation formation. The evolution of the models' lattices in terms of their capacity to restrict interstitials and repair defects revealed that the self-healing/recovery mechanism that confirmed the highest initial lattice distortion value accompanied by the least lattice re-distortion value in the FeNiCrCuAl HEA model is key to the observed superior irradiation tolerance of the HEA models. Thus, by feasibly enhancing lattice distortion in crystalline materials, notably in HEAs, promising and potentially high irradiation-resistant structural materials can be developed.

Simulation of polycrystalline beryllium sputtering by H, D, T atoms

The results of modeling the sputtering coefficients of polycrystalline beryllium by hydrogen isotopes in the range of collision energies of 8 eV-100 keV and their dependences on the angle of incidence of the beam on the surface are presented. This data is necessary for estimating the sputtering of the first wall in the ITER tokamak made from beryllium. A strong surface shape influence on obtained results is shown. The limiting cases of a flat potential barrier (smooth surface) and a spherical potential barrier (a surface consisting of spikes) are considered. The effect of collision cascades on the sputtering coefficient has been established. The dependences of the average depth of sputtered particle formation on the bombarding particles energy are obtained for various angles of beam incidence on the target. The energy spectra and angular dependences of the ejection of sputtered particles are calculated for different energies of bombarding beam atoms. It is shown that the presence of an attractive well in the potential of an incident particle surface changes the sputtering coefficient dependence on incidence angle at small glancing angles. Keywords: Sputtering coefficients, energy and angular distributions of sputtered particles, interatomic potential, hydrogen isotopes, beryllium.

Моделирование распыления поликристаллического бериллия атомами H, D, T

The results of modeling the sputtering coefficients of polycrystalline beryllium by hydrogen isotopes in the range of collision energies of 8 eV–100 keV and their dependences on the angle of incidence of the beam on the surface are presented. This data is necessary for estimating the sputtering of the first wall in the ITER tokamak made from beryllium. A strong surface shape influence on obtained results is shown. The limiting cases of a flat potential barrier (smooth surface) and a spherical potential barrier (a surface consisting of spikes) are considered. The effect of collision cascades on the sputtering coefficient has been established. The dependences of the average depth of sputtered particle formation on the bombarding particles energy are obtained for various angles of beam incidence on the target. The energy spectra and angular dependences of the ejection of sputtered particles are calculated for different energies of bombarding beam atoms. It is shown that the presence of an attractive well in the potential of an incident particle–surface changes the sputtering coefficient dependence on incidence angle at small glancing angles.

Molecular Dynamics Simulations of Displacement Cascade near Precipitate in Zirconium Alloys

Molecular Dynamics Simulations of Displacement Cascade near Precipitate in Zirconium Alloys

Influence of swift heavy ion irradiation on bimetallic gold-silver nanoparticles in dielectric matrices and their optical properties

Nanosized gold-silver (AuAg) alloy nanoparticles (NPs) of sizes, 2 nm -25 nm embedded in fused quartz are synthesized using sequential implantation and post annealing at 900℃ for 1 h in Argon environment. The post annealed film is irradiated using swift heavy ions (SHI), 120 MeV Ag ions to investigate the effect of electronic energy deposition, (Se×ϕ), on size, shape and composition of the alloy NPs. Transmission electron microscopy (TEM) analysis of the as- implanted AuAg film reveals the formation of small sized, 1.8 nm-3.5 nm, bimetallic AuAg NPs. Rutherford backscattering spectroscopy (RBS) spectra along with its fitted graph convey the annealing induced out diffusion, mixing and formation of larger sized, 2 nm -25 nm, alloy NPs through Ostwald ripening. SHI irradiation results in deformation in shape from spherical to ellipsoidal alloy NPs with major axis align along the beam direction and the average aspect ratio is about 1.20. RBS analysis results convey the formation of Ag enriched alloy NPs after irradiation. The smaller nanoparticles are found dissolved while larger ones grow and elongate along the ion beam direction. SPR properties are modified by SHI induced processes of melting, sputtering and re-precipitation in the ion tracks.The un-irradiated film exhibits a single intense SPR peak at 536 nm, while the irradiated film gives rise two SPR peaks: Ist, a blue shifted SPR peak from 536 nm to 515 nm with significantly reduced intensity and much wider FWHM; and, IInd, a small SPR peak around 460 nm. SHI induced modifications on the NPs are understood in terms of thermal spike model. The detailed analysis shows that SHI can be used as a tool to tailor size, shape and composition of the bimetallic AuAg alloy NPs and their SPR properties.

Radiation response of Y3Al5O12 and Nd3+-Y3Al5O12 to Swift heavy ions: insight into structural damage and defect dynamics.

Understanding the behavior of a material under irradiation is paramount to its application in the nuclear industry. The present work explores the radiation response of garnet Y3Al5O12 (YAG) and Nd3+-substituted Y3Al5O12 (Nd-YAG) under a 100 MeV Iodine beam at varying fluences to mimic the effect of fission fragments. This is relevant to the potential application of garnet as a host for minor actinide (MA) transmutation (Nd3+: surrogate for long-lived MA (Am3+, Np3+, Cm3+)). The un-irradiated and irradiated YAG and Nd-YAG samples were investigated by X-ray diffraction and Raman spectroscopy. Positron annihilation spectroscopy, thermal spike modelling and theoretical studies have been employed to understand the role of substitution and defect energetics in influencing this radiation response. Although both materials were not completely amorphized under the present irradiation conditions, a tremendous loss in crystallinity could be observed with increase in fluence, the damage being much more in Nd-YAG. Ion track radii of 2.17 nm and 2.91 nm were estimated for YAG and Nd-YAG respectively. Thermal-spike calculations show an increase in radiation-induced transient temperatures upon Nd-substitution that causes greater radiation damage in Nd-YAG. The enhancement in radiation-induced damage with increasing ion-fluence manifests in broadening and weakening of the Raman modes and XRD peaks. An increase in the average positron annihilation lifetime indicated the creation of oxygen vacancies. The defect formation energies of Y3Al5O12 have been theoretically estimated via density functional theory (DFT) and unfavorable energies required for creating cation pair anti-sites have been proposed as one of the possible reasons for the relatively poorer radiation response of YAG. The irradiation behavior of Y3Al5O12 has been compared with disordered fluorite (YSZ) and zirconate pyrochlores, which are well-researched ceramics for MA transmutation.

Determining role of W+ ions in the densification of TiAlWN thin films grown by hybrid HiPIMS/DCMS technique with no external heating

Hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) with substrate bias synchronized to the high mass metal-ion fluxes was previously proposed as a solution to reduce energy consumption during physical vapor deposition processing and enable coatings on temperature-sensitive substrates. In this approach, no substrate heating is used (substrate temperature is lower than 150 oC) and the thermally activated adatom mobility, necessary to grow dense films, is substituted by overlapping collision cascades induced by heavy ion bombardment and consisting predominantly of low-energy recoils. Here, we present direct evidence for the crucial role of W+ ion irradiation in the densification of Ti0.31Al0.60W0.09N films grown by the hybrid W-HiPIMS/TiAl-DCMS co-sputtering. The peak target current density Jmax on the W target is varied from 0.06 to 0.78 A/cm2 resulting in more than fivefold increase in the number of W+ ions per deposited metal atom, η = W+/(W + Al + Ti) determined by time-resolved ion mass spectrometry analyses performed at the substrate plane under conditions identical to those during film growth. The DCMS is adjusted appropriately to maintain the W content in the films constant at Ti0.31Al0.60W0.09N. The degree of porosity, assessed qualitatively from cross-sectional SEM images and quantitatively from oxygen concentration profiles as well as nanoindentation hardness, is a strong function of η(Jmax). Layers grown with low η values are porous and soft, while those deposited under conditions of high η are dense and hard. Nanoindentation hardness of Ti0.31Al0.60W0.09N films with the highest density is ∼33 GPa, which is very similar to values reported for layers deposited at much higher temperatures (420–500 oC) by conventional metal-ion-based techniques. These results prove that the hybrid HiPIMS/DCMS co-sputtering with bias pulses synchronized to high mass metal ion irradiation can be successfully used to replace conventional solutions. The large energy losses associated with heating of the entire vacuum chamber are avoided, by focusing the energy input to where it is in fact needed, i.e., the workpiece to be coated.

Applying the Inelastic Thermal Spike Model to the Investigation of Damage Induced by High‐Energy Ions in Polymers

AbstractThis 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 ≈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.

Long-timescale transformations of self-interstitial atom clusters of Cu using the SEAKMC method: The effect of setting an activation energy threshold for saddle point searches

On-the-fly kinetic Monte Carlo (kMC), a computational technique for atomistic simulations, has attracted attention because it increases the simulation timescale beyond that of molecular dynamics (MD) simulations while maintaining atomistic fidelity. However, for most kMC methods, when events with high and low activation energies coexist in the event list, trivial events with extremely low activation energies that do not essentially affect the phenomena of interest, so-called flicker events, are frequently selected, making it challenging to observe the key dynamics. In this study, we use Self-Evolving Atomistic kMC (SEAKMC), one of the on-the-fly kMC methods, to model the unstable-to-stable transformations of irregular three-dimensional self-interstitial-atom (SIA) clusters in Cu generated through collision cascade. By setting an activation energy threshold once every five steps, transformations into stable configurations are enhanced. The algorithm renders the simulation timescales one or two orders of magnitude longer than those possible with MD simulations. Further, the probability of transformations into stable configurations is increased by 40 times compared to that of the original SEAKMC method. In addition, we find that the stable configurations obtained by the transformation of the SIA clusters are mostly Frank loops. In summary, this new algorithm for the SEAKMC method helps to resolve the inefficiency of kMC methods resulting from the selection of flicker events and will aid the study of meso-timescale atomistic dynamics.

Development of a semi-empirical interatomic potential appropriate for the radiation defects in V-Ti-Ta-Nb high-entropy alloy

High-entropy alloys (HEAs) hold promise as candidate structural materials in future nuclear energy systems. Body-centred cubic V-Ti-Ta-Nb HEAs have received extensive attention due to their excellent mechanical properties. In this work, the Finnis-Sinclair interatomic potential for quaternary V-Ti-Ta-Nb HEAs has been fitted based on the defect properties obtained with the density functional theory (DFT) calculations. The new potential for Nb accurately reproduces the vacancy formation energy, vacancy migration energy and interstitial formation energy. The typical radiation defect properties predicted by the alloy potential were consistent with the DFT results, including the binding energies between substitutional solute atoms, the binding energy between substitutional atoms and vacancies, and the formation energy of interstitial solute atoms. In addition, the mixing enthalpies of the alloys were also consistent with the DFT results. The present potential can also describe reasonably the collision cascade process of quaternary V-Ti-Ta-Nb HEAs.

A novel method for investigation of the impact of sterilization by gamma radiation on polycaprolactone scaffold

Structural properties of materials irradiated with gamma-rays, such as mechanical and physical properties, may be modified or reduced depending on the displacement damages. Apart from increasing or decreasing that property, damage may be desirable or not. This study investigates the effects of sterilization by gamma radiation on polycaprolactone (PCL) scaffolds. Using a code-based simulation method, MCNPX provides information on primary knock-on atoms, or PKAs, that cause damage. A program has been developed called GAMMATRACK to access PKA information. These PKA data can be used as input for the SRIM code to analyze gamma damage systematically. The rate of damage caused by gamma radiation is calculated on the PCL target. The theoretical calculation method also has been used to confirm the results of the Monte Carlo method (MCNPX + SRIM code). Due to the low-energy PKAs and the thin target possibility of the displacement cascade can be ignored. It is realized that all displacements are due to single vacancies. The total number of hydrogens, carbons, and oxygen PKAs were obtained. It was found that the number of carbons PKA is more than the others, which causes three-dimensional polymer networks to be created. In the experimental analysis, it is necessary to know the appropriate depth of the sample for damage investigation. GAMMATRACK gives the gamma displacement damage graph along the length of the PCL. It shows a uniform distribution of displacement damage. The damage rate for the PCL target is calculated, and the results between the theoretical calculations and the Monte Carlo method (MCNPX + SRIM code) differ by about 17%.

Illustrating the atomic structure and formation mechanism of ion tracks in polyethylene terephthalate with molecular dynamics simulations

This work reports molecular dynamics (MD) simulations of the formation of detailed ion track structures at the atomic scale in polymers. To simulate the initial chemical reactions and the subsequent thermal movement of polymer molecules, an adapted thermal spike model was implemented using a charge-implicit reactive force field potential. The MD simulation reproduces the physical–chemical process of ion track formation observed in the experiment, e.g., the bond breakage and creation, gas production and release, carbonization effect, and the relative radial density distributions, which are consistent with small angle X-ray scattering results of ion tracks in polyethylene terephthalate generated with 15.9 keV nm−1 Au and 10.9 keV nm−1 Xe ions, respectively. Based on the MD simulation, the ion tracks in polymers show a heavily-damaged core region with an inhomogeneous nanoporous structure, and a surrounding transition region with the mass density increasing gradually back to the same value as the pristine sample.