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This study investigates the stability of Inconel–Cu Multimetallic Layered Composites (MMLCs) in nuclear reactor applications using Molecular Dynamics simulations. The focus is on understanding the underlying mechanisms governing the properties of MMLCs for advanced nuclear reactors, specifically, the mechanochemistry of the interface between Inconel and copper alloys. The selection of Inconel–Cu MMLCs is primarily due to copper's superior thermal conductivity, enhancing heat management within reactors by preventing hotspots and ensuring uniform temperature distribution. This research examines Incoloy 800H and two Inconel variants (718 and 625), assessing their stability at 1000 K after exposure to 10 keV collision cascades up to 0.12 dpa. Notable findings include defect clustering on the {1 2 0} family of planes of Inconel and Cu, with Stacking Faults and Lomer–Cottrell locks on the Inconel side. [ABSTRACT FROM AUTHOR]

In this work we studied the effects of 20 keV collision cascades in alpha iron with a 1/2〈111〉{110} edge dipole using molecular dynamics. We analysed three different cases: a) the primary knock-on atom (PKA) is centred between both dislocations, b) the PKA is closer to one of the dislocations, and c) the PKA is on top of one of the dislocations and directed towards it. Our calculations show enhanced formation of vacancy clusters in the bulk for intermediate distances due to the absorption of self-interstitials by the dislocation during the collision cascade reducing the recombination between vacancies and self-interstitials. This effect results in the formation of jogs at the dislocation and the consequent climb due to the absorption of the self-interstitials. As a result, there is an unbalance between vacancies and self-interstitials produced by the collision cascade, with a significantly larger number of vacancies than self-interstitials in the bulk and the formation of large vacancy clusters. When the collision cascade develops directly on top of the dislocation, jogs are formed due to both the absorption of vacancies and self-interstitials, inducing climb and with the total dislocation length increasing up to several nanometers.

In the paper, the distributions of structure damage created in alpha-phase of gallium oxide by keV fluorine, phosphorus and xenon ion irradiation, have been obtained at room temperature. A noticeable effect of the average individual collision cascade density on the stable damage production efficiency at the surface was established. In contrast to many other semiconductors, an intermediate damage peak appeared in the alpha-Ga2O3 between the surface and bulk maxima. This intermediate peak visible in the RBS/C spectra at low damage levels was discovered for the first time. Characteristic peculiarities of the discovered maximum were investigated.

We study radiation damage accumulation in alpha polymorph of gallium oxide (α-Ga2O3) epitaxial layers under irradiation with 40 keV monatomic P and 140 keV molecular PF4 ions. The distribution of stable structural damage is bimodal in both cases. The growth rate of the surface disordered layer under PF4 ion irradiation is significantly higher than that under monatomic P ion bombardment. At the same time, monatomic ion irradiation is more efficient in the bulk defect peak formation. Thus, the density of displacement cascades strongly affects the formation of stable damage in α-gallium oxide. The doses required to create the same level of disorder in the metastable α-polymorph are higher than that in the thermodynamically stable α-. Mechanisms of damage formation in these polymorphs are different. [ABSTRACT FROM AUTHOR]

This study investigates the stability of Inconel–Cu Multimetallic Layered Composites (MMLCs) in nuclear reactor applications using Molecular Dynamics simulations. The focus is on understanding the underlying mechanisms governing the properties of MMLCs for advanced nuclear reactors, specifically, the mechanochemistry of the interface between Inconel and copper alloys. The selection of Inconel–Cu MMLCs is primarily due to copper’s superior thermal conductivity, enhancing heat management within reactors by preventing hotspots and ensuring uniform temperature distribution. This research examines Incoloy 800H and two Inconel variants (718 and 625), assessing their stability at 1000 K after exposure to 10 keV collision cascades up to 0.12 dpa. Notable findings include defect clustering on the {1 2 0} family of planes of Inconel and Cu, with Stacking Faults and Lomer–Cottrell locks on the Inconel side.

A comprehensive statistical treatment is conducted to analyse the outcomes of MD simulations of collision cascades in α-titanium in a wide range of primary knocked-on atoms (PKAs) energy 5 keV 25 keV and irradiation temperature 100 K 900 K. The fractions of vacancies and interstitial atoms in clusters of point defects formed in individual cascades and their average values and , the average sizes of vacancy and interstitial clusters, and the average number of vacancy and interstitial clusters per cascade are evaluated. The physical mechanisms that determine the dependence of , , , , , and on simulation parameters have been proposed. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were applied to study primary damage formation in collision cascades initiated by the recoil of primary knock-on atoms (PKAs) with PKA energies = 5, 10, 15, 20, and 25 keV in α-Ti at temperature T = 100, 300, 600, and 900 K. A statistical sample of 24 collision cascades per set of parameters was generated in order to assure statistical reliability of the obtained results. The size of the sampling set was justified posteriori using a simple procedure. The number of Frenkel pairs, , and cascade relaxation time were obtained as functions of . It was found that the average values fit into ≈0.3NRT if the threshold displacement energy is selected in the range of 28–40 eV depending on the irradiation temperature. At high PKA energies/low temperatures, collision cascades in α-Ti tend to break up into subcascades elongated along the trajectories of high-energy recoil atoms and their relaxation time does not depend on . At low PKA energies/high temperatures, equiaxed collision cascades dominate and their relaxation time increases monotonically with increasing PKA energy . [ABSTRACT FROM AUTHOR]

α‐type Ti35 alloy (Ti‐6 wt%Ta) has been recommended as one of the candidate materials for advanced nuclear reactors due to its excellent overall performance. Nonetheless, irradiation effects on the alloy remain scarcely understood by far. Herein, the primary irradiation damage of Ti35 alloy is investigated from multiple perspectives using atomistic simulations. Results show that with the increasing energy of the primary knock‐on atom (2 keV ≤ EPKA ≤ 10 keV), the number of Frenkel pairs (NFP) gradually increases independent of the incident direction of PKA (IDPKA) and the ambient temperature (100 K ≤ T ≤ 700 K), while it exhibits a downtrend at each IDPKA as the T elevates. The magnitude of EPKA can affect the anisotropy of IDPKA on irradiation damage. Unrelated to EPKA, IDPKA, and T, di‐interstitial clusters and Nvacancy > 3 clusters respectively account for the largest proportion of their categories, highlighting their stability. In any case, vacancies are more prone to cluster than interstitials. The increase of EPKA has a greater effect on vacancy clustering than interstitial clustering but can promote the increase in both the clustering fractions. An important insight into the understanding of the irradiation damage behaviors for the alloy has been provided. [ABSTRACT FROM AUTHOR]

Energy loss during interactions between high-energy particles and target materials mainly consists of nuclear and electronic energy losses. Electronic stopping and electron-phonon coupling effects are two different mechanisms that reflect electronic energy loss effects. To accurately simulate the irradiation damage process of high-energy particles, it is necessary to solve the key scientific problem of the influence of electronic energy loss on irradiation damage. This paper reviews the most recent progress on the irradiation damage behavior study of several key structural materials under the influence of electronic energy loss effects, elaborates the effects of electronic stopping, electron-phonon coupling, and electronic thermal conductivity on irradiation defects. The influence laws of electronic energy loss effects on the irradiation damage of target materialsare summarized and the existing problems in the research of high-energy particle irradiation of target materials are highlighted. Finally, the prospectives are outlined for future research directions.

Abstract—Molecular dynamics (MD) simulations were applied to study radiation damage formation in collision cascades initiated by primary knock-on atoms (PKA) with PKA energy EРКА = 5, 10, 15, and 20 keV in α-Ti at T = 100, 300, 600, and 900 K ambient temperatures. A series of 24 collision cascades was simulated for each (EРКА, Т) pair. The necessary sampling set size was justified by a simple a posteriori procedure. The number of Frenkel pairs and the fraction of vacancies, , and self-interstitial atoms (SIAs), εi, in point defect clusters were evaluated as functions of (EРКА, Т). It was established that collision cascades in α-Ti are extended along PKA trajectories and tend to split into subcascades. In contrast to other elemental metals with close-packed crystal structure, in collision cascades in α-Ti. Moreover, both and demonstrate weak temperature dependence. This is an indirect indication that both vacancy and SIA clusters created in collision cascades in α-Ti are stable in the considered temperature range. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive examination of the physical mechanisms driving hardening in irradiated face-centered cubic FeNiCr alloys. The evolution of irradiation-induced defects during shear deformation is modeled by atomistic simulations through overlapping cascade simulations, where the nucleation and evolution of dislocation loops is validated by transmission electron microscopy images obtained from irradiated FeNiCr alloys using tandem accelerator. The effect of different shear rates on the microstructure of irradiated materials with a specific focus on the changes in the density of voids and dislocation loops induced by irradiation was analyzed. Additionally, the fundamental interaction processes between single irradiation-induced defects contributing to irradiation hardening, such as voids and dislocation loops in the alloy are explained. The analysis at atomic level indicates that both the dislocation loops and the voids exhibit strengthening effects. Furthermore, the nanometric voids are much stronger obstacles than dislocation loops of comparable size. The mechanism of cutting the voids leads to an increase of voids density and thus contributes to an increase in irradiation hardening. The mechanism of collapse of small voids into dislocation loops leads to decrease of voids density and at the same time increase of loops density. The coupling effect between the density of voids and dislocation loops is determined. Finally, the novel, physical mechanisms-based model of irradiation hardening and dislocation-radiation defect reaction kinetics are developed, which consider the mechanisms of void cutting, void shrink and void collapse to dislocation loop. • Atomistic insight into the mechanisms of radiation nano-damage generation. • Defects modeled by atomistic simulations through overlapping cascade simulations. • Explanation of fundamental interaction processes between single defects. • New irradiation hardening model proposed based on the physical mechanisms. [ABSTRACT FROM AUTHOR]

Understanding irradiation damage involves a multi-scale and multi-physics approach, integrating data from experiments, simulations and phenomenological models. This paper focuses on its early stages, specifically neutron-induced collision cascades in zirconium, as nuclear-grade zirconium alloys are widely used in fuel assemblies. We have gathered and analysed a significant sample of results from high-fidelity, large-scale molecular dynamics (MD) simulations, employing existing interatomic potentials and the two-temperature model to account for electron–phonon coupling. Our data can be directly applied to higher-scale methods. Furthermore, we carried out a comprehensive statistical analysis of the features associated with the defect production, including the number of defects, their distribution and size of the affected area. As a result, we developed a generative model of collision cascades that is parametric, hierarchical and stochastic, i.e. it takes into account a statistical nature of the phenomenon, is interpretable and shareable. This model has been developed with three primary objectives: to provide a sufficient descriptor of a cascade, to interpolate data obtained from high-fidelity simulations, and to demonstrate that the statistical model can produce representative distributions of primary irradiation defects. The results can be used to generate synthetic inputs for models at longer length and time scales, to provide fast approximations that take into account the morphology of introduced defects, and in general to serve as a powerful analytical tool. [ABSTRACT FROM AUTHOR]

The irradiation response of yttria-stabilized zirconia, having different grain sizes, subjected to 900 keV iodine ions at room temperature and 1000 K is reported. GIXRD and Raman spectroscopy indicate superior radiation tolerance of the fine-grained samples when compared to their coarse-grained counterparts which is attributed to the abundance of grain boundaries at relatively shorter distances. A reduction in the residual strain is observed in the samples irradiated at 1000 K. This is attributed to the clustering of the irradiation induced point defects thereby resulting in a decrease in their density, but with a corresponding increase in the extended defects density. [ABSTRACT FROM AUTHOR]

The high stochasticity of collision cascades makes running large sets of molecular dynamics simulations mandatory to obtain meaningful statistics. The convergence of the number of defects and of clusters and of the Primary Knock-On Atom (PKA) penetration depth with respect to the number of simulations in the sets is investigated for PKAs of 1 keV and 5 keV in Si. Two methods for setting the initial directions of the PKAs are compared: one is entirely based on randomness and the other integrates symmetry considerations. The latter method eases the convergence of the results. Larger sets are needed to converge the PKA depth than the number of clusters and defects. We observe that the higher the energy of the PKA, the harder it gets to reach the convergence. We find that large sets of simulations enables to get rid of the influence of the initial position of the PKA. [ABSTRACT FROM AUTHOR]

The mobility of a 1 / 2 〈 111 〉 { 110 } edge dipole in alpha-iron has been studied using molecular dynamics simulations. Collision cascades generated by keV recoils have been shown to induce the migration of dislocations. In order to elucidate the origin of the motion of these dislocations, and separate the production of defects from temperature or pressure effects, a stressed region of different shapes (sphere and cylinder) is simulated close to the edge dipole. We observe that the generated shock wave triggers the movement of the dislocations even when no defects are produced. The shape of the distorted region and the character of the dislocations influence the way the dislocations move, due to the change in Peach-Koehler force direction and to the fact that the shock waves arrive to the different parts of the dislocations at different times. [ABSTRACT FROM AUTHOR]

The sensitivity of collision cascades simulations to the Two-Temperature Model main parameters is investigated by performing an extensive statistical study both in Si and Ge materials. The purpose is to identify the parameters of the Two-Temperature Model whose impact is the most significant on the cascades properties and to discuss the physical role of each parameter. We demonstrate that the electronic stopping power and electron–phonon coupling have a drastic impact both in Si and Ge but that these two parameters act differently on those two materials due to their distinct thermal properties. We show that the formation of thermal spikes and therefore of amorphous pockets is sensitive to the electronic specific heat. The effects are again very distinct in Si and in Ge. The influence of both the threshold velocity for the stopping power and the electron–phonon coupling activation time are found to be negligible at the considered energies. [ABSTRACT FROM AUTHOR]

For a few decades now, molecular dynamics (MD) simulations have been extensively used for studying primary damage formation in collision cascades in materials exposed to fast particle irradiation. Because of the stochastic nature of defect production phenomena, it is vital to model collision cascades in batches with the same set of essential simulation parameters that includes primary knock-on atom (PKA) energy and target temperature in the first instance. No generally accepted practice has been established so far to determine the optimal size of the sampling set of MD simulations of collision cascades. The suggested simple a posteriori sampling set size validation method is based on reviewing the dependence of the average and median number of Frenkel pairs generated in collision cascades on the amount n of simulated cascades in a series with identical simulation parameters. As the average and median number of Frenkel pairs converges with raising n , the optimal sampling set size is determined as a function of the simulation conditions. It is shown how it depends on the PKA energy, irradiation temperature, alloy composition and the interaction of collision cascades with the free surfaces. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were applied to study radiation damage formation in collision cascades initiated by primary knock-on atoms (PKA) with energy E PKA = 5, 10, 15 and 20 keV in pure nickel at temperature T = 100, 300, 600, 900 and 1200 K. A series of 24 collision cascades per E PKA , T set was simulated to assure statistical reliability of the results. The number of Frenkel pairs, N FP , the fraction of vacancies, σ vac , and self-interstitials (SIA), σ SIA , in point defect clusters, the average size of vacancy and SIA clusters, N vac and N SIA , respectively, and the average vacancy and SIA cluster per cascade yield, Y vac and Y SIA , respectively, were evaluated as functions of E PKA , T . It is found that N FP ∝ E PKA under all simulated conditions. Both σ vac and σ SIA demonstrate similar dependence on E PKA . σ vac matches Y vac , while σ SIA correlates with N SIA and is affected by SIA diffusivity. N vac is determined by the irradiation temperature and thermal stability of vacancy clusters. They are stable at T ⩽ 300 K and N vac ∝ E PKA , whereas at 600 K ⩽ T ⩽ 900 K, N vac ≈ 6 and 10, which corresponds to the sizes of regular stacking fault tetrahedra. SIA cluster per cascade yield Y SIA ∝ N FP and therefore ∝ E PKA under all simulated irradiation conditions. [ABSTRACT FROM AUTHOR]

The interaction of collision cascades initialized by alpha decays in PuO 2 crystals with xenon, helium and mixed Xe-He bubbles of linear dimensions of 1–2 nm was studied by a molecular dynamics technique. The bubbles were not destroyed by the cascades studied, however individual fast Xe and He atoms could be released. These fast atoms received high energies up to 90% of the collision cascade energy (80 keV). Also, the diffusion migration of helium atoms to the region of the crystal lattice damaged by the collision cascade was detected. Xenon atoms did not diffuse to the damage area on the simulated time scale. However, the xenon clusters changed their shape in the disordered surroundings. [ABSTRACT FROM AUTHOR]

The release of clusters from the surface of PuO 2 nanocrystals caused by the alpha decay collision cascades was simulated using the molecular dynamics. The clusters containing up to several hundred particles were recorded. The obtained size distributions of the clusters were characterized by relatively high probabilities of the formation of large clusters. The total kinetic energy of the released material reached tens of percent of the total energy of the collision cascade. Single ions, both plutonium and oxygen, could have kinetic energies of up to several thousand electron-volts. The electric charge of the clusters in most cases was close to zero, although clusters with significant negative charges were also observed. [ABSTRACT FROM AUTHOR]

The process of radiation damage formation in collision cascades initiated by primary knock-on atoms (PKAs) with energy EPKA = 5, 10, 15, and 20 keV in nickel at temperatures T = 100, 300, 600, 900, and 1200 K was studied using the molecular dynamics method. To ensure the statistical validity of the results, a series of 24 cascades was modeled for each pair of (EPKA, T) parameters. The simulation results were analyzed to determine the number NFP of Frenkel pairs, fractions of vacancies σvac and interstitial atoms σSIA in clusters of point defects, average sizes of vacancy 〈Nvac〉 and interstitial 〈NSIA〉 clusters, and average numbers of vacancy 〈Yvac〉 and interstitial 〈YSIA〉 clusters produced in collision cascades as functions of the PKA energy and simulation temperature. It was found that the relation 〈NFP〉 = 2 ± 0.9 × holds true at all the examined values of (EPKA, T). The functional dependences of 〈σvac〉 and 〈σSIA〉 on EPKA were identical. The dependence of 〈σvac〉 follows that of 〈Yvac〉, while 〈σSIA〉 is governed by 〈NSIA〉 and the mobility of interstitials. The value of 〈Nvac〉 depends on the irradiation temperature and the thermal stability of vacancy clusters. These clusters are stable at T ≤ 300 K, and 〈Nvac〉 ∝ EPKA; at 600 ≤ T ≤ 900 K, 〈Nvac〉 ≈ 6 and 10, which corresponds to the sizes of regular stacking fault tetrahedra. The value of 〈YSIA〉 is proportional to 〈NFP〉 and, consequently, to EPKA in the entire range of PKA energies. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were employed to study radiation damage created in collision cascades in L1 0 TiAl intermetallic compound and fcc Ti-50at.%Al disordered solid solution. Either Al or Ti primary knock-on atoms (PKA) with PKA energy 5 keV ⩽ E PKA ⩽ 20 keV were initiated in the two materials at temperature T ranging from 100 K to 1200 K. From 36 to 48 different cascades for each ( E PKA , T) set were simulated in order to emulate an isotropic spatial and random temporal distribution of PKAs, generate representative sampling and obtain statistically reliable quantitative results. The number of Frenkel pairs, 〈 N FP γ - TiAl 〉 and 〈 N FP Ti - 50 Al 〉 , formed in L1 0 TiAl intermetallics and Ti-50at.%Al disordered solid solution, respectively, and averaged over collision cascades with the same ( E PKA , T) was used as a quantitative measure of radiation resistance against primary damage formation. It is shown that the relationship 〈 N FP γ - TiAl 〉 ⩽ 〈 N FP Ti - 50 Al 〉 is fulfilled under all simulation conditions, i.e. L1 0 ordered crystal structure of TiAl intermetallics is essential for its high radiation tolerance. However, a relatively high resistance to the formation of primary radiation defects is retained even after complete disordering of L1 0 TiAl that points out to the existence of additional mechanisms contributing to its radiation tolerance. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were applied to study primary damage formation in collision cascades initiated by primary knock-on atoms (PKA) with energy E PKA = 5 , 10, 15 and 20 keV in aluminum at temperature T = 100 , 300 and 600 K. A series of 24 collision cascades for each E PKA , T set was simulated in order to assure statistical reliability of the obtained results. The number of Frenkel pairs, fraction of vacancies σ vac and self-interstitials (SIA) σ SIA in point defect clusters, the average vacancy N vac and SIA N SIA cluster size, the average vacancy Y vac and SIA Y SIA cluster per cascade yield and the average cascade relaxation time τ c were evaluated as a function of E PKA , T . It was established that collision cascades in aluminium split into subcascades along the projectile trajectory. As a result, σ vac , σ SIA , N vac , N SIA and τ c do not depend on E PKA . [ABSTRACT FROM AUTHOR]

Computer modelling by molecular dynamics (MD) was employed to study radiation damage created in collision cascades in L1 2 Ni 3 Al intermetallic compound. Either Al or Ni primary knock-on atoms (PKA) with PKA energy 5 keV ≤ E P K A ≤ 20 keV were initiated in the intermetallic crystals at ambient temperatures 100 K ≤ T ≤ 1200 K. At least 24 different cascades for each ( E P K A , T , PKA type) set were simulated in order to mimic an isotropic spatial and random temporal distribution of PKAs. The total yield of nearly 1000 simulated cascades provides the largest yet reported sampling to get statistically reliable quantitative results. The obtained MD simulation data were analysed to get the number of Frenkel pairs, the fraction of point defects in point defect clusters, the fraction of Al and Ni vacancies, self-interstitial atoms (SIA) and anti-sites created in collision cascades as a function of ( E P K A , T , PKA type). It was found that under identical simulation conditions, collision cascades in L1 2 Ni 3 Al initiated by Al PKAs generate more radiation damage, whereas collision cascades initiated by Ni PKAs produce more chemical disorder. Preferred formation of Ni SIAs in collision cascades in Ni 3 Al was observed under all ambient temperatures and PKA energies. • Collision cascades in Ni 3 Al were modelled over a wide temperature and PKA energy range. • The number of Frenkel pairs and anti-sites are found as a function of ( E P K A , T). • Collision cascades initiated by Al PKAs generate more radiation damage. • Collision cascades initiated by Ni PKAs generate more disorder. • Preferred formation of Ni SIAs was observed under all temperatures and PKA energies. [ABSTRACT FROM AUTHOR]

Abstract A molecular dynamics study of radiation damage created in collision cascades in D0 19 Ti 3 Al intermetallic compound and a Ti-Al binary disordered solid solution with the same chemical composition is carried out. Collision cascades are initiated by either Al or Ti primary knock-on atoms (PKA) with PKA energy 5 keV ≤ E P K A ≤ 20 keV in the two materials at temperature T ranging from 100 K to 900 K. A series of at least 32 different cascades for each ( E P K A , T) set was simulated in order to imitate an isotropic spatial and random temporal distribution of PKAs, generate representative sampling and obtain statistically reliable quantitative results. The numbers of Frenkel pairs, 〈 N F P α 2 〉 and 〈 N F P α 〉 , formed in D0 19 Ti 3 Al intermetallics and Ti-25at.%Al disordered solid solution, respectively, were averaged over collision cascades with the same ( E P K A , T) and used to quantify the radiation resistance against primary damage formation. It is shown that the relationship 〈 N F P α 2 〉 ≤ 〈 N F P α 〉 is satisfied under all simulation conditions, i.e. D0 19 ordered crystal structure of Ti 3 Al intermetallics is an important feature affecting its radiation tolerance. Nevertheless, a relatively high resistance against the formation of primary radiation defects has been retained even after complete disordering of D0 19 Ti 3 Al, which points out to the existence of additional mechanisms governing its radiation tolerance. Highlights • High radiation tolerance of α 2 -Ti 3 Al is determined by its ordered crystal structure. • Primary damage in Ti 3 Al is compared with that in Ti-25at.%Al disordered solid solution. • Notable fraction of high radiation tolerance of Ti 3 Al is retained after disordering. • Other PKA energy dissipation mechanisms contribute to radiation tolerance of α 2 -Ti 3 Al. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A BCA-MD method with adaptive volume to simulate cascades in solids is proposed. • The MD cell is adapted and optimized for each cascade using BCA results. • The BCA-MD reproduces very well the different phases of cascades. • The speedup of MD calculations achieved by the BCA-MD increases with the PKA energy. • A speedup of ×312 was estimated for a PKA energy of 0.5 MeV in Fe. Abstract We present a method combining the Binary Collision Approximation (BCA) and Molecular Dynamics (MD) with adaptive volume to simulate high-energy collision cascades in solids under irradiation. The results obtained with the BCA-MD method with adaptive volume are in very good agreement with those obtained with full MD calculations. The BCA-MD predicts very well in a broad range of Primary Knock-on Atom (PKA) energies the different phases of evolution of the cascade, the number of Frenkel pairs, the fraction of point defects in clusters and their size distribution. The BCA-MD method proposed here achieves a considerable acceleration of MD simulations with a speedup factor that increases with the PKA energy. For a PKA energy of 80 keV in Fe, the speedup measured is higher than 30. For a PKA energy of 0.5 MeV in Fe, by comparison with MD simulations performed by other authors, we estimate that the BCA-MD accelerates MD simulations by a factor 312. [ABSTRACT FROM AUTHOR]

Experiments with irradiated single-walled carbon nanotubes are shown to generate a set of probability distribution functions and to derive a set of information theoretic entropy-based parameters. Energetic Cs + ions initiate linear collision cascades and nonlinear thermal spikes in single-walled carbon nanotubes. The probability distribution functions are constructed from the normalized experimental yields of the sputtered atoms and clusters. The information or Shannon entropy and fractal dimension are evaluated for each of the emitted species. Along with the fractal dimension, the information is used to identify and distinguish the energy dissipation processes that generate conditions for monatomic sputtering and clusters emissions. [ABSTRACT FROM AUTHOR]

Hydrogenated diamond-like carbon films produced by C 3 H 6 deposition at 5 kV and implanted at room temperature with 30 keV Co atoms to 12 at.% show not only a bimodal distribution of Co atoms but also a massive redistribution of hydrogen in the films. Resonant nuclear reaction analysis was used to measure the hydrogen depth profiles (15N-method). Depletion of hydrogen near the surface was measured to be as low as 7 at.% followed by hydrogen accumulation from 27 to 35 at.%. A model is proposed considering the thermal energy deposited by collision cascade for thermal insulators. In this model, sufficient energy is provided for dissociated hydrogen to diffuse out of the sample from the surface and diffuse into the sample towards the interface which is however limited by the range of the incoming Co ions. At a hydrogen concentration of ∼35 at.%, the concentration gradient of the mobile unbounded hydrogen atoms is neutralised effectively stopping diffusion towards the interface. The results point towards new routes of controlling the composition and distribution of elements at the nanoscale within a base matrix without using any heat treatment methods. Exploring these opportunities can lead to a new horizon of materials and device engineering needed for enabling advanced technologies and applications. [ABSTRACT FROM AUTHOR]

Tungsten (W) is the prime candidate material for the divertor and other plasma-facing components in DEMO. The point defects (i.e. vacancies and self-interstitials) produced in collision cascades caused by incident neutrons aggregate into dislocation loops (and voids), which strongly affect the mechanical properties. The point defects also interact with existing microstructural features, and understanding these processes is crucial for modelling the long term microstructural evolution of the material under fusion conditions. In this work, we performed molecular dynamics simulations of cascades interacting with initially straight edge dislocation dipoles. It was found that the residual vacancy number usually exceeds the residual interstitial number for cascades interacting with vacancy type dipoles, but for interstitial type dipoles these are close. We observed that a cascade near a dislocation promotes climb, i.e. it facilitates the movement of point defects along the climb direction. We also observed that the dislocations move easily along the glide direction, and that kinks are formed near the centre of the cascade, which then facilitate the movement of the dipoles. Some dipoles are sheared off by the cascade, and this is dependent on PKA energy, position, direction, and the width of dipole. [ABSTRACT FROM AUTHOR]

The Gaussian approximation potential (GAP) is an accurate machine-learning interatomic potential that was recently extended to include the description of radiation effects. In this study, we seek to validate a faster version of GAP, known as tabulated GAP (tabGAP), by modelling primary radiation damage in 50–50 W–Mo alloys and pure W using classical molecular dynamics. We find that W–Mo exhibits a similar number of surviving defects as in pure W. We also observe W–Mo to possess both more efficient recombination of defects produced during the initial phase of the cascades, and in some cases, unlike pure W, recombination of all defects after the cascades cooled down. Furthermore, we observe that the tabGAP is two orders of magnitude faster than GAP, but produces a comparable number of surviving defects and cluster sizes. A small difference is noted in the fraction of interstitials that are bound into clusters. [ABSTRACT FROM AUTHOR]

The reliability of atomistic simulations of primary radiation damage hinges on the quality of the interatomic potential. However, irradiation induced collision cascades involve strongly non-equilibrium processes, and thus depend on properties of potentials not usually included in the potential fitting. Here, we compare the predictions of five interatomic potentials for tungsten in cascade simulations with primary knock-on energies ranging from threshold energies for defect production, up to 200 keV. The highest energies represent the energetic recoils induced by the 14 MeV fusion neutron irradiation. We further compare properties related to dynamic collisions predicted by the different potentials to DFT calculations, to assess the accuracy of these predictions. We also present two hardened versions of a recent EAM-type potential, and demonstrate explicitly the importance of carefully adjusting the range of the potential at interaction distances smaller than those included in the fitting of potentials to equilibrium properties. [ABSTRACT FROM AUTHOR]

Experiments and simulations both have verified the presence of 〈 100 〉 dislocations in irradiated W. It is essential to know the properties and behavior of these defects to study the evolution of microstructures at higher scales. We study the thermal stability and transition mechanism of various 〈 100 〉 dislocations formed in a molecular dynamics (MD) database of 230 collision cascades using three different interatomic potentials. The activation energy to transition to more stable 〈 111 〉 dislocations is found for various 〈 100 〉 dislocation defects that transition within the 100 nanosecond time scale that is readily accessible to MD. The stability of 〈 100 〉 dislocations increases with size, but the trend is not strict. The reasons for irregularities are the aspects of internal configuration such as (i) the arrangement of 〈 100 〉 directed crowdions within the defect, (ii) the presence and arrangement of non- 〈 100 〉 crowdions on the fringes of the defect. We show the typical pathways of transitions and discuss the sources of instability in the defect configurations. We also discuss the similarities and differences in stability found across different interatomic potentials. Understanding transition mechanisms and internal morphology gives insights into the stability of 〈 100 〉 dislocations, useful in higher scale models such as Kinetic Monte Carlo (KMC). [ABSTRACT FROM AUTHOR]

In this article, a large scale multi-particle molecular dynamics (MD) simulation model was developed to study the dynamic structural changes in single crystal diamond under 5 keV Ga + irradiation in conjunction with a transmission electron microscopy (TEM) experiment. The results show that the thickness of ion-induced damaged layer (∼9.0 nm) obtained from experiments and simulations has good accordance, which demonstrates the high accuracy achieved by the developed MD model. Using this model, the evolution of atomic defects, the spatial distributions of implanted Ga particles and the thermal spike at the very core collision area were analysed. The local thermal recrystallizations observed during each single ion collision process and the increase of the density of the non-diamond phase (mostly sp 2 bonded) at irradiation area are fund to be the underling mechanisms responsible for ion fluence dependent amorphization of diamond observed in previous experiments. [ABSTRACT FROM AUTHOR]

We use molecular dynamics to study radiation-induced mixing between low solid solubility metals, focusing on the effect of liquid phase properties, by sequentially performing multiple 10keV collision cascade simulations up to a total dose of ~5 displacements per atom (dpa). We find mixing to be proportional to the square root of dose, independent of interface crystallography, and highly sensitive to liquid phase interdiffusivity. It occurs primarily by liquid phase interdiffusion in thermal spikes rather than by ballistic displacements. Partial de-mixing is also seen within thermal spikes, regardless of liquid phase solubility. We attribute it to segregation of impurities into the liquid core of the thermal spikes. We present an expression that relates mixing rates to liquid phase heats of mixing and self-diffusivities. [ABSTRACT FROM AUTHOR]

Density functional theory models developed over the past decade provide unique information about the structure of nanoscale defects produced by irradiation and about the nature of short-range interaction between radiation defects, clustering of defects, and their migration pathways. These ab initio models, involving no experimental input parameters, appear to be as quantitatively accurate and informative as the most advanced experimental techniques developed for the observation of radiation damage phenomena. Density functional theory models have effectively created a new paradigm for the scientific investigation and assessment of radiation damage effects, offering new insight into the origin of temperature- and dose-dependent response of materials to irradiation, a problem of pivotal significance for applications. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics (MD) has been applied to simulate the radiation damage created in displacement cascades in D019 Ti3Al structural intermetallics. Collision cascades formed by the recoil of either Al or Ti primary knock-on atoms (PKA) with energy =5, 10, 15 or 20keV were considered in Ti3Al single crystals at T =100, 300, 600 and 900K. At least 24 different cascades for each (E PKA, T, PKA type) set were simulated. A comprehensive treatment of the modelling results has been carried out. We have evaluated the number of Frenkel pairs, fraction of Al and Ti vacancies, self-interstitial atoms and anti-sites as a function of ( , PKA type). Preferred formation of both Al vacancies and self-interstitial atoms in D019 Ti3Al exposed to irradiation has been detected. [Copyright &y& Elsevier]

Abstract: The velocity-Verlet molecular dynamics has been applied to study the radiation damage created in collision cascades in an aluminium crystal harbouring an isolated edge dislocation with Burgers vector. The total of more than 150 displacement cascades formed by the recoil of primary knock-on atoms with energy in crystals at temperatures were simulated. Three different mechanisms of the interaction of collision cascades with edge dislocations in aluminium have been observed. At low and room temperatures the dislocations climb by absorption of displaced atoms from the collision cascade region. Capture of vacancies and displaced atoms by dislocation core at high temperatures leads to dislocation climb up and down. At room and especially at high temperatures dislocation climb by absorbing displaced atoms is accompanied by the formation of stacking fault tetrahedra in the vicinity of the dislocation line. In order to quantify the redistribution of radiation defects, the number of residual vacancies and self-interstitials created in collision cascades near edge dislocations was evaluated and compared with the number of Frenkel pairs formed in collision cascades in the pristine material under the same irradiation conditions. [Copyright &y& Elsevier]