Simulation Of Radiation Damage Research Articles

Sensitivity of ion implantation to low-energy electronic stopping cross-sections

Clarifying the sensitivity of ion implantation to low-energy electronic stopping cross-sections (ESCS) is critical to assess different ESCS for simulating radiation damage in the fields like materials science, space exploration and electronic industry. The Monte Carlo code IM3D improved with a users’ ESCS module and a proposed analytical model are used to investigate the sensitivity of ion depth distribution to different ESCS including Stopping and Range of Ions in Matter (SRIM), Binary Theory (BT) and Unitary Convolution Approximation (UCA) at low energies (lower than 75 keV/u). The analytical model is consistent with IM3D well and thus provides a simple way to assess arbitrary ESCS. We found that the larger the ratio of electronic to nuclear energy loss is, the stronger sensitivity of ion depth distribution to ESCS is. Based on the assessment, the upgraded SRIM database and BT with the shell correction for light ions while UCA with the Bloch correction for heavy ions are recommended for simulating ion implantation to agree with experimental results.

Chemical ordering effect on the radiation resistance of a CoNiCrFeMn high-entropy alloy

The chemical ordering of CoNiCrFeMn and its effect on radiation resistance is analyzed in this study via Monte Carlo (MC) annealing simulation and molecular dynamics (MD) radiation damage simulation. MC annealing at a lower temperature of 600 K forms an initial stage Cr-rich region in CoNiCrFeMn due to a strong chemical ordering-driven phase decomposition; whereas, annealing at a higher temperature of 1100 K forms a chemical short-range order (CSRO). MD radiation damage simulation shows that the Cr-rich region formed by 600 K annealing accelerates the aggregation and the evolution of defects, facilitating more dislocation loops formation. On the other hand, the CSRO structure formed by 1100 K annealing effectively delays the growth of defect number and tends to reduce the dislocation density and defect diffusion, suggesting better radiation resistance. However, the CSRO structure is destroyed by radiation, thus these advantages of CSRO will disappear in due time if CSRO cannot heal. Fortunately, since the CSRO can recover at working temperature of 1100 K, we speculate that under the working temperature of 1100 K and with a modest radiation damage rate, the advantages of CSRO can maintain for a long time. We finally discuss the condition of the CSRO preservation by proposing a CSRO radiation damage – diffusion healing competition model.

A Review on DPA for computing radiation damage simulation

A Monte Carlo code is developed for the radiation damage in the metals which results from nuclear collisions that create energetic recoil atoms of the host material. The development of the simulation codes for the radiation damage method by neutrons and protons can be highly useful in technology of advanced nuclear systems and nuclear fusion reactors. The aim of this review is to investigate the impact of the radiation damage in the materials by the neutron and proton energy irradiation. The damage parameter used in the evaluation is displacement per atom (DPA) in material as a function of neutron and proton energy. For this purpose, there are some software codes used which are related to radiation damage because radiation damage can be measured as a function of DPA, which is one of the critical issues for high intensity beams, particularly, for protons and neutrons.

Simulation of radiation damage via alpha decay in BFS:PC grouts using 4He2+ ion acceleration

The impact of alpha radiation on cements used to encapsulate intermediate-level waste (ILW) is not well understood. ILW wastes can contain high levels of alpha-emitting radionuclides, meaning that the grouts used to encapsulate them are exposed to significant ionising radiation. Thus, a damaged region could develop in the grout adjacent to the alpha-emitting species. This work attempted to recreate this behaviour through nonradioactive 4He2+ ion-accelerator experiments, which have not previously been applied to common encapsulation grouts. The influence of this irradiation on a slag-Portland cement was investigated at different ages via transmission electron microscopy energy-dispersive x-ray spectroscopy (TEM-EDX) and supporting techniques, to assess whether 4He2+ irradiation caused textural or chemical zonation. No significant changes in hydrate phases or textures were observed, other than minor variations associated with carbonation. This paper provides a proof of concept for using ion acceleration techniques on cements and furthers knowledge on their radiation response.

Study of Degradation Mechanisms of Strength and Thermal-Physical Properties of Nitride and Carbide Ceramics-Promising Materials for Nuclear Energy.

The dependences of changes in the strength properties of nitride and carbide ceramics under high temperature irradiation with Kr15+ and Xe22+ heavy ions at irradiation doses of 1012–1015 ions/cm2 are presented in this work. The irradiation was chosen to simulate radiation damage processes that are closest to the real conditions of reactor tests in operating modes of increased temperatures. Polycrystalline ceramics based on AlN, Si3N4 nitrides, and SiC carbides were chosen as objects of research, as they have great prospects for use as a basis for structural materials for high-temperature nuclear reactors, as well as materials for nuclear waste disposal. During these studies the effect of radiation damage caused by irradiation with different fluences on the change in mechanical strength and hardness were determined, and the mechanisms causing these changes depending on the type of irradiated materials were proposed. The novelty of this study is in the results obtained determining the stability of the strength and thermophysical parameters of nitride and carbide ceramics exposed to high-temperature irradiation, which made it possible to determine the main stages and mechanisms for changing these parameters depending on the accumulated radiation damage. The relevance of this study consists not only in obtaining new data on the properties of structural materials exposed to ionizing radiation, but also in the possibility of determining the mechanisms of radiation damage in ceramics.

Molecular dynamics simulations of radiation damage in YBa2Cu3O7

The advent of high-temperature superconductors (HTS) with high field strengths offers the possibility of building smaller, cheaper magnetically confined fusion reactors. However, bombardment by high energy neutrons ejected from the fusion reaction may damage the HTS tapes and impair their operation. Recreating the conditions present in an operational fusion reactor is experimentally challenging, therefore, this work uses molecular dynamics simulations to understand how radiation modifies the underlying crystal structure of YBa2Cu3O7. To facilitate the simulations a new potential was developed that allowed exchange of Cu ions between the two symmetrically distinct sites without modifying the structure. Radiation damage cascades predict the formation of amorphous regions surrounded by regions decorated with Cu and O defects found in the CuO-chains. The simulations suggest that the level of recombination that occurs is relatively low, resulting in a large number of remnant defects and that there is a no substantial temperature effect.

4D evolution of Cr23C6 precipitates in neutron-irradiated and annealed HT-UPS steel observed via synchrotron micro-computed tomography

High-temperature-ultrafine precipitate strengthened (HT-UPS) steel is a potential structural material for advanced nuclear reactors; however, its irradiation response is not well understood. This research provides insight into irradiation-induced effects, such as precipitate evolution mechanisms and four-dimensional morphological evolution, in HT-UPS steel using synchrotron micro-computed tomography. Identical specimens were characterized pre-irradiation and post-irradiation following neutron exposure up to 0.3 displacements per atom at 600 °C. Irradiation effects were also differentiated from the annealing response of precipitates. Following neutron irradiation, the average Cr23C6 precipitate size reduced, affected by the synergy of nucleation and growth, ballistic dissolution, and inverse coarsening, which was observed at fluences an order of magnitude lower than previously observed. Annealing at 600 °C for 32 h increased the average Cr23C6 precipitate size and decreased the phase fraction, attributed to precipitate coarsening. The precipitate morphology evolution and resultant mechanisms can be utilized to parameterize and validate microstructural models simulating radiation damage or annealing.Graphical abstract

Front-end investigations of the coated particles of nuclear fuel samples – ion polishing method

The investigations of the coated-particles of nuclear fuel samples are carried out in three stages: front-end, irradiation in the reactor core, and post-irradiation examination. The front-end stage is the initial analysis of the failures rates of produced samples before they are placed in the reactor core. The purpose of the verification is to prepare the particles for an experiment that will determine the degree of damage to the coated particles at each stage. Before starting experiments with the samples, they must be properly prepared. Polishing the samples in order to uncover the inner layers is an important, initial experimental step. The authors of this paper used a novel way to prepare samples for testing - by applying an ion polisher. Mechanical polishing used frequently for sample preparations generates additional mechanical damages in the studied fuel particle, thus directly affecting the experimental results. The polishing methods were compared for three different coated particles using diagnostic methods such as Raman spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy. Based on the obtained results, it was concluded that the ion polishing method is better because the level of interference with the structures of the individual layers of the tested samples is much lower than with the mechanical method. The same technique is used for the fuel particles undergone ion implantation simulating radiation damage that can occur in the reactor core.

Molecular dynamics simulation of primary radiation damage in W-Ta alloys: Effect of tantalum

Tungsten (W) and W-based alloys are competitive candidates for plasma-facing materials in future fusion reactors. W-tantalum (Ta) alloys get the most attention amongst these materials. The present study uses molecular dynamics simulations to study the displacement cascades of pure W and W-Ta alloy systems with recoil energy up to 100 keV at 300 K and the further evolution of cascade defects at 1,000 K. The effects of Ta concentration on the generation and evolution of the defects, produced with primary knock-on atom energies, are quantitatively analysed. This study's results show that the presence of randomly distributed Ta atoms does not significantly affect the average number of surviving Frenkel pairs or the fractions of clustered vacancies and interstitials. In addition, there is no completed vacancy dislocation loop in all systems after cascading. The produced dislocation loops are mainly 1/2 〈111〉 loops companied with a small amount of 〈100〉 loops and mixed loops. However, the existence of Ta atoms slows down the motion of defects and defect mobility decreases as the Ta concentration increases in bulk W. This will affect the size and density of defects. In addition, the presence of Ta also inhibits the transition of the 〈100〉 dislocation loops to 1/2 〈111〉 dislocation loops under the high-temperature condition. This will affect the types of dislocation loops and the material performance.

Probing the displacement damage mechanism in Si, Ge, GaAs by defects evolution analysis

With the rapid development of space technology, the requirements for the radiation resistance of solar cells are higher and higher.A clear understanding of the radiation damage mechanism of materials is very important for radiation hardening of space solar cells. Therefore, molecular dynamics (MD) method was utilized to simulate the irradiated defects evolution in mainly used materials (Si, Ge, and GaAs) for multi-junction solar cells. By simulating the cascade collision process took placed in different materials under different interatomic potential, it is determined that Tersoff potential was more suitable for radiation damage simulation of semiconductor materials.By comparing the number of Frenkel pair defects (FPs) produced in the three materials during irradiation, the radiation resistance of each material was obtained. The MD results were verified by comparing with empirical NRT model.The displacement evolution of off-site atoms and the final clusters formed by point defects, i.e. interstitials and vacancies were further quantitatively analyzed. The atomic image of irradiated defects provides new physical insights for displacement damage mechanism and gives better understanding for explaining the degradation of irradiated multi-junction solar cells.

Primary radiation damage in silicon from the viewpoint of a machine learning interatomic potential

Characterization of the primary damage is the starting point in describing and predicting the irradiation-induced damage in materials. So far, primary damage has been described by traditional interatomic potentials in molecular dynamics simulations. Here, we employ a Gaussian approximation machine-learning potential (GAP) to study the primary damage in silicon with close to ab initio precision level. We report detailed analysis of cascade simulations derived from our modified Si GAP, which has already shown its reliability for simulating radiation damage in silicon. Major differences in the picture of primary damage predicted by machine-learning potential compared to classical potentials are atomic mixing, defect state at the heat spike phase, defect clustering, and recrystallization rate. Atomic mixing is higher in the GAP description by a factor of two. GAP shows considerably higher number of coordination defects at the heat spike phase and the number of displaced atoms is noticeably greater in GAP. Surviving defects are dominantly isolated defects and small clusters, rather than large clusters, in GAP's prediction. The pattern by which the cascades are evolving is also different in GAP, having more expanded form compared to the locally compact form with classical potentials. Moreover, recovery of the generated defects at the heat spike phase take places with higher efficiency in GAP. We also provide the attributes of the new defect cluster that we had introduced in our previous study. A cluster of four defects, in which a central vacancy is surrounded by three split interstitials, where the surrounding atoms are all 4-folded bonded. The cluster shows higher occurrence in simulations with the GAP potential. The formation energy of the defect is 5.57 eV and it remains stable up to 700 K, at least for 30 ps. The Arrhenius equation predicts the lifetime of the cluster to be $0.0725\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$ at room temperature.

Effect of irradiation with heavy Xe22+ ions with energies of 165–230 MeV on change in optical characteristics of ZrO2 ceramic

The aim of this work is to study the effect of irradiation with heavy Xe22+ ions with energies of 165 MeV, 200 MeV, and 230 MeV on the change in the optical properties of ZrO2 ceramic. The choice of ion energies, as well as irradiation fluences of 1013-1014 ion/cm2, is primarily due to the possibility of simulating radiation damage in ceramics that occurs when overlapping damaged areas in the material, comparable to damage from fission fragments of uranium nuclei in an atomic reactor. Using UV–Vis spectroscopy methods, changes in the throughput of ceramics were evaluated depending on the irradiation fluence and the energy of incident ions. It was found that a change in the irradiation conditions leads to the formation of irradiation-induced defects with an energy of 2.4–2.45 eV in the structure, the concentration of which increases with the irradiation dose. Changes in the band gap and refractive index depending on irradiation fluence and incident ions energy indicate a change in the electronic and optical density of ceramics, as well as the formation of additional absorbing centers in the structure.

Atomic Simulations of U-Mo under Irradiation: A New Angular Dependent Potential

Uranium-Molybdenum alloy has been a promising option in the production of metallic nuclear fuels, where the introduction of Molybdenum enhances mechanical properties, corrosion resistance, and dimensional stability of fuel components. Meanwhile, few potential options for molecular dynamics simulations of U and its alloys have been reported due to the difficulty in the description of the directional effects within atomic interactions, mainly induced by itinerant f-electron behaviors. In the present study, a new angular dependent potential formalism proposed by the author’s group has been further applied to the description of the U-Mo systems, which has achieved a moderately well reproduction of macroscopic properties such as lattice constants and elastic constants of reference phases. Moreover, the potential has been further improved to more accurately describe the threshold displacement energy surface at intermediate and short atomic distances. Simulations of primary radiation damage in solid solutions of the U-Mo system have also been carried out and an uplift in the residual defect population has been observed when the Mo content decreases to around 5 wt.%, which corroborates the negative role of local Mo depletion in mitigation of irradiation damage and consequent swelling behavior.

Atomistic simulation of displacement damage and effective nonionizing energy loss in InAs

A molecular dynamics (MD) method, along with the analytical bond-order potential, is applied to study defect production in InAs. This potential is modified to obtain a better description for point-defect properties and is extended for proper applications in radiation damage simulation. By using this modified potential, the threshold displacement energy $({E}_{d})$, as one of the crucial parameters in radiation damage studies, is calculated over thousands of crystallographic directions for incorporating spatial anisotropy. However, the ${E}_{d}$ dependence on directions is found to be relatively weak. The defect production, clustering, and evolution in InAs are further investigated for the energies of the primary knock-on atom (PKA) ranging from 500 eV to 40 keV. A nonlinear defect production is seen with increasing PKA energy. This nonlinearity, which is associated with the direct-impact amorphization, is very distinctive for PKA energies ranging from 1 to 20 keV. Based on the damage density evaluated from molecular dynamics simulations, a theoretical model is developed for determining nonionizing energy loss (NIEL), which can be used for quantifying the electronic device degradation in a space radiation environment. The NIELs of InAs for proton, alpha, and Xe particles are calculated from the displacement threshold up to 60 MeV in comparison with available data so as to validate our model in the current study.

Исследование радиационной устойчивости боросиликатного стекла к бета-и гамма-излучению с помощью ускоренных протонов

Preservation of the main physical and chemical properties of vitrified high-level waste over a long-time period under the influence of heavy radiation exposure is considered as an essential criterion for its quality assessment used to demonstrate the safety of intermediate storage under controlled conditions and subsequent final disposal of the waste. Earlier calculations covering a time period of up to 104 years allowed to identify the maximum beta- and gamma-radiation induced dose loads for borosilicate glass (BSS) of a basic composition specifically designed to vitrify liquid HLW from ODC MCC [1]. This study evaluates potential feasibility of applying an accelerated proton beam to simulate radiation damage according to the type of beta-gamma effects produced on the BSS and investigates the consequences of such effects on its properties which is seen as a distinctive feature of this research.

Effects of high-energetic 3He+ ion irradiation on tungsten-based composites

The interaction of plasma and its encompassing materials with one another is one of the principle designing issues of fusion reactors. Tungsten is considered one of the primary candidate materials in fusion applications due to its superior properties. In this work, we doped vanadium carbide powders to the tungsten matrix to enhance the properties of tungsten alloys. Tungsten-based composites, which irradiated with 2.5 MeV 3He+ ions at room temperature, were analyzed by atomic force microscopy (AFM) in order to obtain surface morpohologies after irradiation. Helium ion irradiated tungsten-based composites were studied by using XRD, neutron diffraction technique, raman spectroscopy, and positron annihilation spectroscopy to reveal the microstructural changes. XRD and ND analyses clarified the changes in the crystal structures of the tungsten-based materials after He ion irradiation. The simulation of radiation damage and the calculation of displacements per atom (DPA) was also determined by the SRIM code. SRIM showed that the maximum helium concentration in the specimens takes place in the depth range of 58–65 nm. The crystallite size of tungsten-based composites slightly increased after helium ion irradiation. AFM results revealed that the maximum size of bubbles on the surface of tungsten-based composites shape under 100 nm. Positron annihilation spectroscopy studies of the specimens have been discussed before and after 3He+ ion irradiation.

REQUIREMENTS FOR THE DUAL Fe + H/He BEAM AT THE ACCELERATOR HIPR FOR SIMULATION OF NEUTRON INFLUENCE ON NUCLEAR REACTOR MATERIALS

Ion accelerator facility is a powerful tool that can be used to simulate neutron irradiation effects in reactor materials. At the NRC “Kurchatov Institute” - ITEP the heavy-ion accelerator HIPr is used for the ion-beam simulation of radiation damage in steels and alloys. Irradiation is provided with the wide range of metal ions (mainly Fe2+). It is essential to include helium and hydrogen beams for the proper simulation of transmutation driven mechanisms of swelling and void formation. Energies, beam line angle and intensity are determined for design of the second beam line for He/H implantation at HIPr.

Parallel optimization of the Crystal-KMC on Tianhe-2

The Kinetic Monte Carlo (KMC) is one of the commonly used methods for simulating radiation damage of materials. Our team develops a parallel KMC software named Crystal-KMC, which supports the Embedded Atom Method (EAM) potential energy and utilizes the Message Passing Interface (MPI) technology to simulate the vacancy transition of the Copper (Cu) element under neutron radiation. To make better use of the computing power of modern supercomputers, we develop the parallel efficiency optimization model for the Crystal-KMC on Tianhe-2, to achieve a larger simulation of the damage process of materials under irradiation environment. Firstly, we analyze the performance bottleneck of the Crystal-KMC software and use the MIC offload statement to implement the operation of key modules of the software on the MIC coprocessor. We use OpenMP to develop parallel optimization for the Crystal-KMC, combined with existing MPI inter-process communication optimization, finally achieving hybrid parallel optimization. The experimental results show that in the single-node CPU and MIC collaborative parallel mode, the speedup of the calculation hotspot reaches 30.1, and the speedup of the overall software reaches 7.43.

Multiple cascade radiation damage simulations of pyrochlore

ABSTRACT We report molecular dynamics simulations of multiple radiation damage cascades in the pyrochlores Gd2Ti2O7 and Gd2Zr2O7 and the solid solution Gd2(Zr x Ti1–x )2O7 (x = 0.25, 0.50, 0.75). Using a simulation cell of 360,448 atoms, for each compound 2200 decay events are simulated over a total time of 10 ns, with each recoiling uranium atom (primary-knock-on atom) assigned initial kinetic energy of 5 keV. The structures generated are analysed using Steinhardt local order parameters. There is a large increase in volume for the Ti pyrochlore associated with a transition to an amorphous structure which resembles the melt while preserving the local environment of the Ti. The calculated dose for amorphisation is 20 eV atom−1 which compares well with experiment overlap of cascade and damage accumulation drives the amorphisation suppressessing the healing mechanisms. The behaviour of the zirconate is different – the substantial anion disorder produced by each recoil event is followed by healing and reversion to the parent pyrochlore. In the solid solution the onset of amorphisation is delayed to later times on increasing the Zr concentration and overall swelling reduced. Our simulations highlight the importance of ion mobility, associated with the weaker Zr–O bonds, in healing.

Method of information entropy for convergence assessment of molecular dynamics simulations

The lack of a reliable method to evaluate the convergence of molecular dynamics simulations has contributed to discrepancies in different areas of molecular dynamics. In the present work, the method of information entropy is introduced to molecular dynamics for stationarity assessment. The Shannon information entropy formalism is used to monitor the convergence of the atom motion to a steady state in a continuous spatial domain and is also used to assess the stationarity of calculated multidimensional fields such as the temperature field in a discrete spatial domain. It is demonstrated in this work that monitoring the information entropy of the atom position matrix provides a clear indicator of reaching steady state in radiation damage simulations, non-equilibrium molecular dynamics thermal conductivity computations, and simulations of Poiseuille and Couette flow in nanochannels. A main advantage of the present technique is that it is non-local and relies on fundamental quantities available in all molecular dynamics simulations. Unlike monitoring average temperature, the technique is applicable to simulations that conserve total energy such as reverse non-equilibrium molecular dynamics thermal conductivity computations and to simulations where energy dissipates through a boundary as in radiation damage simulations. The method is applied to simulations of iron using the Tersoff/ZBL splined potential, silicon using the Stillinger–Weber potential, and to Lennard–Jones fluid. Its applicability to both solids and fluids shows that the technique has potential for generalization to other areas in molecular dynamics.