High-energy Particle Irradiation Research Articles

Structural modification mechanism of Fe-based amorphous alloys by high-energy particle irradiation

High-energy particle irradiation-induced crystallization technology presents remarkable potential for precise nanostructure design. However, the fundamental mechanism behind this process remains a long-standing unsolved puzzle. In this paper, we used a high-energy electron beam as the irradiation source and amorphous Fe85B15 alloy as a model system to investigate the behavior of irradiation-induced structural changes. Our experimental results show that the nucleation barrier in irradiation-induced crystallization ranges from 0.5 to 0.8 eV, depending on the temperature, much smaller than that observed in thermal-induced crystallization. Additionally, the nucleation entropy observed is −1.60 × 10−3 eV/K, and the entropic contribution to the nucleation barrier dominates over the enthalpic contribution. This paper provides compelling experimental evidence demonstrating that nucleation in irradiation-induced crystallization is not a thermally activated effect; instead, it is a process in which the amorphous state progresses through a series of intermediate short-range ordering configurations toward a crystalline state with the assistance of irradiation-induced atomic rearrangement.

Self-interstitial atom properties in Nb–Mo–Ta–W alloys

Self-interstitial atoms (SIA) are generated in collision cascades during high-energy particle irradiation of crystalline materials. In pure metals, SIA generally adopt split configurations and display fast mobilities along one-dimensional trajectories. This differentiates them from vacancies, which move in confined three-dimensional paths. This asymmetry is one of the pillars of irradiation damage theories that have been successful in explaining a number features of the irradiation response of pure metals and dilute alloys. However, in complex concentrated alloys consisting of several metallic elements in equal or near equal proportions, lattice distortions associated with compositional fluctuations change the potential energy landscape on atomic scales, leading to SIA structures not seen in their pure metal counterparts. In this paper, we use atomistic simulations to study the properties of self-interstitial atoms in the quaternary equiatomic Nb–Mo–Ta–W refractory alloy. Chemically, these SIA defects adopt a variety of structures involving all pairs of atoms. We find the 〈111〉 orientation to be the most common among all split configurations, but we also observe – surprisingly – a relatively high occurrence of octahedral SIA. In terms of their diffusivities, we find two clearly distinguished regimes below and above 600 K, where the SIA diffusion changes dimensionality from 1D to 3D. We calculate the migration energies and diffusion pre-factors in both regions, from which we extract the translational and rotational components of the defect migration. We find values of 0.25 eV and pre-factors of ∼10−11 m2 s−1 in the low temperature regime, and 0.57 eV and ∼10−8 m2 s−1 in the high temperature one. From this, we estimate a rotational energy barrier of 0.37 eV.

Multi-Directional Displacement Threshold Energy and Crystal Irradiation Damage Model

Subject to intense high-energy particle irradiation, various effects manifest within a material. Specifically, when high-energy particles collide with lattice atoms in a crystal material, a sequence of interactions is set in motion, initiating irradiation effects. Using GaAs solar cells as an example, this study investigates how potential barriers in different directions of atoms in sphalerite structures affect atomic displacement and establishes a probability model for lattice atomic displacement under proton irradiation. By combining Markov chains, changes in displacement threshold energy with different crystal orientations are described, and a damage model for cascading collision relationships that cause irradiation effects is established. Finally, the new model is compared to classical models, and differences in defects caused by proton impacts at several energies on GaAs crystals are simulated.

Estimation of different calculation models for evaluating heavy ion-induced damage in plasma facing materials

In a fusion reactor, plasma-facing materials are bombarded by various energetic particles (such as neutrons) from fusion reactions, leading to inevitable irradiation damages. These damages can significantly affect the material servicing life time and threaten the safety of fusion reactors. Accurate and consistent evaluation of irradiation damage is quite important to investigate the evolution mechanism of irradiation defect. In this study, the irradiation damage of tungsten caused by high-energy particles were evaluated using the SRIM code and molecular dynamics simulations. The accuracy of three atomic displacements calculation models, i.e., VAC model, NRT model, and arc-dpa model, under two computational modes of SRIM (the K-P mode and F-C mode) were discussed. It was found that with the increase of the incident particle atomic number, the peak depth of displacement moved to the shallow layer and increased in peak height, while the trend was opposite with the increase of the incident particle energy. As to the different calculation modes, the F-C and K-P modes produced a ratio of vacancies of about 1.8 times in the VAC model. What's more, the VAC model and NRT model predicted results consistent with molecular dynamics simulation results at lower energy ranges (approximately <100 eV), but deviated from them as the energy increased. In contrast, the arc-dpa model exhibited good consistency with the molecular dynamics simulations and had higher accuracy. Therefore, it is recommended to use the arc-dpa model under the K-P mode for the calculation of atomic displacement. This model can accurately and quickly calculate the irradiation damage level caused by high-energy particle irradiation in fusion reactors.

Effects of proton and oxygen ion irradiation on cardiovascular function and structure in a rabbit model

PurposeAstronauts on missions beyond low Earth orbit will be exposed to galactic cosmic radiation, and there is concern about potential adverse cardiovascular effects. Most of the research to identify cardiovascular risk of space radiation has been performed in rodent models. To aid in the translation of research results to humans, the current study identified long-term effects of high-energy charged particle irradiation on cardiovascular function and structure in a larger non-rodent animal model. Materials and methodsAt the age of 12 months, male New Zealand white rabbits were exposed to whole-body protons (250 MeV) or oxygen ions (16O, 600 MeV/n) at a dose of 0 or 0.5 Gy and were followed for 12 months after irradiation. Ultrasonography was used to measure in vivo cardiac function and blood flow parameters at 10- and 12-months post-irradiation. At 12 months after irradiation, blood cell counts and blood chemistry values were assessed, and cardiac tissue and aorta were collected for histological as well as molecular and biochemical analyses. Plasma was used for metabolomic analysis and to quantify common markers of cardiac injury. ResultsA small but significant decrease in the percentage of circulating lymphocytes and an increase in neutrophil percentage was seen 12 months after 0.5 Gy protons, while 16O exposure resulted in an increase in monocyte percentage. Markers of cardiac injury, cardiac troponin I (cTnI) and N-Terminal pro-B-type Natriuretic Peptide were modestly increased in the proton group, and cTnI was also increased after 16O. On the other hand, metabolomics on plasma at 12 months revealed no changes. Both types of irradiation demonstrated alterations in cardiac mitochondrial morphology and an increase in left ventricular protein levels of inflammatory cell marker CD68. However, changes in cardiac function were only mild. ConclusionLow dose charged particle irradiation caused mild long-term changes in inflammatory markers, cardiac function, and structure in the rabbit heart, in line with previous studies in mouse and rat models.

Proton irradiation induced damage effects in CH&lt;sub&gt;3&lt;/sub&gt;NH&lt;sub&gt;3&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;-based perovskite solar cells

Perovskite solar cells (PSCs) have a great potential for space applications due to their high specific power, low cost and high defect tolerance. PSCs used in space will be subjected to high-energy particle irradiation, especially proton irradiation, resulting in the decline of photovoltaic (PV) performance. However, the research on proton irradiation effects in PSCs is still in its infancy stage. In this work, the CH&lt;sub&gt;3&lt;/sub&gt;NH&lt;sub&gt;3&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt; (MAPbI&lt;sub&gt;3&lt;/sub&gt;) thin films and their PSCs are irradiated by protons with energy of 0.1, 2, 10, 20 MeV, etc. Irradiation-induced changes in PV parameters of the PSCs are studied as a function of proton fluence. The structural and surface morphological changes of the irradiated MAPbI&lt;sub&gt;3&lt;/sub&gt; films and Au electrode layers of PSCs are characterized by X-ray diffraction and scanning electron microscopy. In addition, UV spectrophotometer is also employed to analyze the transmission loss in glass substrate induced by proton irradiation. It is found that PSCs exhibit superior resistance against proton irradiation. The PV properties of the PSCs don’t degrade after 0.1 MeV (2 MeV) proton irradiation up to a fluence of 1×10&lt;sup&gt;13&lt;/sup&gt; p/cm&lt;sup&gt;2&lt;/sup&gt; (1×10&lt;sup&gt;14&lt;/sup&gt; p/cm&lt;sup&gt;2&lt;/sup&gt;). The irradiation-induced damage in the charge transport layers may be the main cause for the performance degradation of PSCs. The gaseous products (NH&lt;sub&gt;3&lt;/sub&gt; and CH&lt;sub&gt;3&lt;/sub&gt;I) of perovskite decomposition eventually lead to exfoliation of the top Au electrode from the PSCs. Regarding 10 and 20 MeV proton irradiation with larger projected ion ranges, the irradiations create color center defects in glass substrate of PSCs, which results in a decrease in light transmission of visible spectrum. However, the color center defects, specifically non-bridging oxygen hole centers, will be partly annealed at room temperature or 100 ℃, reducing the transmission loss in glass. The reported results may help predict the performance degradation of PSCs in space irradiation environment.

Effects of proton and electron irradiations on the dielectric properties of epoxy/anhydride cured products

Recently, epoxy resin materials have shown great advantages in both aerospace and nuclear applications. In order to investigate the aging behaviours of epoxy resin cured products under the irradiation of high-energy particles, we subjected self-prepared epoxy materials to proton and electron irradiation tests under different conditions. Various reductions in permittivity and dielectric loss tangent were observed under all four test conditions. Then, the relationships between the changes in dielectric properties and chemical structures are discussed.

Energetically favorable dislocation/nanobubble bypass mechanism in irradiation conditions

With exposure to high-energy particle irradiation, structural metals develop a number of nanoscale defects, one of which is the nano-sized He bubble. Formed throughout the material, these bubbles can directly impair the movement of dislocations and dramatically alter mechanical performance. Propagating edge dislocations in face-centered cubic metals, driven under sufficient mechanical forces, are expected to cut through He bubbles, due to the higher energetic expense. Here, using atomistic simulations for a model Cu material, we find that when the He-vacancy ratio and bubble diameter become sufficiently large and the ratio of the bubble spacing to the diameter is reduced below a threshold, an extended edge dislocation engages in a multi-step-bypass (MSB) maneuver to change its glide plane and overcome the bubble at room temperature. This unanticipated MSB mechanism provides a more energetically favorable pathway compared to conventional bypass mechanisms under these severe conditions.

Modeling irradiation-induced intragranular gas bubble in tungsten under external tensile loading

Microstructure damage created by high-energy particle irradiation has an inevitable effect on the performance of material. Helium (He) as the transmutation element in irradiated solid prefers to occupy the vacancy (V) center to form HeV complex, which in turn induces the formation of He bubble. Herein, the external applied stress driven irradiation-induced He bubble formation and evolution in single-crystalline tungsten (W) has been investigated using the phase-field method. Importantly, the trapping and resolution kinetic behavior between He atom and He bubble is described by the diffusion coefficient in terms of rate theory continuum model, and the effect of external stress on the movements of vacancy, self-interstitial and He atom has been implemented into their diffusivities as well. We first concentrate on the intrinsic lattice distortion (stress) patterns of void and bubble to validate the developed model by comparing the reported numerical results. Then, the accelerated growth velocity of bubble along the loading direction is predicted, which agrees well with the previously observed stress pattern around the void/bubble. The evolution behaviors of the stress-assisted single, bi-dispersed and multiple bubbles vary with the direction and magnitude of external loading, indicating a strong correlation between the size and density of bubble and the loading level. It is found that with the contribution of increasing external stress, more bubbles can be generated at the formation stage and visible bubbles tend to reduce at the coarsening stage due to bubble coalescence.

Cosmic ray irradiation of comet nuclei: a possible source of cometary outbursts at large heliocentric distances

ABSTRACT The effect of radical accumulation in ice, under high energy particle irradiation at low temperature followed by the energy release during heating, has been proposed as a possible cause of cometary outbursts. Water ice samples were subjected to 15 MeV protons to simulate the cosmic ray irradiation of comet nuclei. The irradiation with 0.9 MeV electrons was performed to model a similar process on icy satellites located in radiation belts of planets. We observed the release of accumulated energy 20 J g−1 during the heating of the proton-irradiated ice with two pulses of fast self-heating of the sample at 84 and 110 K. Similar energy release occurred between 82 and 110 K in the electron-irradiated ice. Our calculations suggest that the recombination of radicals accumulated in the surface layer of a comet nucleus under cosmic ray bombardment can trigger the cometary outbursts far from the Sun.

Radiation stability of mixed tin–lead halide perovskites: Implications for space applications

Mixed organic-inorganic halide perovskite solar cells (PSCs) have received considerable attention in recent years for their impressive solar to electrical power efficiency gains and potentially lower material and processing costs for optoelectronic applications. In addition to terrestrial applications, PSCs are of interest to the space power markets for their low cost, low weight, adaptability to flexible architectures, and tolerance to high energy particle irradiation (mainly protons and electrons). Here we investigate the properties of mixed formamidinium-methylammonium tin-lead iodide (FASn)0.6(MAPb)0.4I3 perovskites which lower the lead content as well as the bandgap, making them attractive for the low bandgap absorber material in tandem PSCs. Through current density-voltage (JV) characterization at lower temperatures, majority carrier transport is hindered and a barrier to photogenerated carrier extraction is evident. This is attributed to the thermally induced change of the bandgap of the absorber layer relative to the energy selective contacts in the device. We find that although the architecture used here hinders the performance at temperatures below 225 K, the tolerance to high energy (3.7 MeV) protons is impressive, considerably out-performing commercially available thin-film CIGS. These results suggest further improvements to structural and interface stability as well as lightweight encapsulation could lead to all perovskite flexible tandem arrays deployed for power generation on missions to low Earth orbit, the moon, Mars, and beyond.

Molecular dynamic simulations evaluating the effect of the stacking fault energy on defect formations in face-centered cubic metals subjected to high-energy particle irradiation

Austenitic stainless steels, which are used as incore structural materials in light water reactors, are characterized by an extremely low stacking fault energy (SFE) among face-centered cubic (FCC) metals. To evaluate the effects of SFE on defect formation under high-energy particle irradiation, molecular dynamics simulations were performed using the interatomic potential sets for FCC metals with different SFEs and a primary knock-on atom energy (EPKA) of 100 keV at 600 K. The results show that the number of residual defects is independent of the SFE. However, the characteristics of self-interstitial atom (SIA) clusters do depend on the SFE. For clusters smaller than a certain size, the ratio of glissile SIA clusters decreases as the SFE increases, which is similar to the trend observed at the low EPKA. However, for larger clusters, which can be detected only at a high EPKA, the ratio of glissile clusters increases. These results correspond to static energy calculations, in which the difference in the formation energy between a Frank loop and perfect loop (ΔEF-P) for the small clusters decreases as the SFE increases. In contrast, for the larger clusters, the SFE dependence of ΔEF-P changes due to the shape restrictions of stable perfect loops. At a high temperature of 600 K, large vacancy clusters with stacking faults can be detected at EPKA = 100 keV, resulting in the enhanced formation of these clusters at lower SFEs. Furthermore, several of these clusters were similar to perfect loops, with the edges split into two partial dislocations with stacking faults, although the largest clusters detected at low EPKAs were similar to stacking fault tetrahedrons.

Effects of Low Dose Space Radiation Exposures on the Splenic Metabolome.

Future space missions will include a return to the Moon and long duration deep space roundtrip missions to Mars. Leaving the protection that Low Earth Orbit provides will unavoidably expose astronauts to higher cumulative doses of space radiation, in addition to other stressors, e.g., microgravity. Immune regulation is known to be impacted by both radiation and spaceflight and it remains to be seen whether prolonged effects that will be encountered in deep space can have an adverse impact on health. In this study, we investigated the effects in the overall metabolism of three different low dose radiation exposures (γ-rays, 16O, and 56Fe) in spleens from male C57BL/6 mice at 1, 2, and 4 months after exposure. Forty metabolites were identified with significant enrichment in purine metabolism, tricarboxylic acid cycle, fatty acids, acylcarnitines, and amino acids. Early perturbations were more prominent in the γ irradiated samples, while later responses shifted towards more prominent responses in groups with high energy particle irradiations. Regression analysis showed a positive correlation of the abundance of identified fatty acids with time and a negative association with γ-rays, while the degradation pathway of purines was positively associated with time. Taken together, there is a strong suggestion of mitochondrial implication and the possibility of long-term effects on DNA repair and nucleotide pools following radiation exposure.

Effects of alloying elements Mn, Mo, Ti, Si, P and C on the incubation period of void swelling in austenitic stainless steels

Void swelling, which induces the degradation of the original properties of nuclear materials under high-energy particle-irradiation, is an important problem. The incubation period, a transient stage before the steady void growth, determines the duration of service of nuclear materials. Several experimental studies have been performed on void observations by transmission electron microscopy (TEM), which, however, has a resolution limit for the size of defect clusters. Positron annihilation lifetime spectroscopy (PALS) enables the detection of small vacancy clusters, single vacancies, dislocations and precipitates. The use of these two methods provides complementary information toward detecting defect information in the incubation period. Here, defect structures during the incubation period in austenitic stainless steels, by means of PALS and TEM are reviewed. The role of alloying elements into determining the period is explained. Furthermore, the existing problems and research directions in this field are presented.

Relating Gain Degradation to Defects Production in Neutron-Irradiated 4H-SiC Transistors

Wide-gap semiconductor SiC is generally considered as a superior candidate for high-radiation applications, due to its higher displacement energy for both Si and C lattice atoms. In this work, we find that the current gain ( $\beta $ ) of 4H-SiC bipolar junction transistors (BJTs) can severely deteriorate after neutron irradiation. Deep-level transient spectroscopy (DLTS) reveals that two major carrier-killer centers, Z1/2 and EH6/7, were produced in neutron-irradiated devices. Surprisingly, we find that the shallow Z1/2 center can play a dominant role over the deep EH6/7 defects in carrier recombination under high-injection conditions, which contributes to the unusual smaller hole capture cross section than that of the electron one, as indicated by the first-principles calculations. Finally, technology computer aided design (TCAD) simulation confirms that the enhanced carrier recombination from the Z1/2 centers is responsible for the degraded performance of SiC BJTs after irradiation. Our findings not only provide a deep insight into the underlying physics for displacement damage in SiC BJTs, but also are of interest for technological applications field related to high-energy particle irradiation or implantation.

Numerical Simulation of Damage Effect for Ferroelectric RAM Irradiated by Space High-Energy Particles

In order to simulate the damage effect of space high-energy particle interacting on ferroelectric random access memory (RAM), the theoretical model of laser supported detonation wave is derived. Also, the equivalent target model of the collision between the core region of the ferroelectric RAM and high-energy particles is established. The high-energy oxygen and nitrogen atoms are selected as the sources of high-energy particles in the air at normal temperature and pressure. The source of particles that bombard the ferroelectric RAM is used to simplify the simulation of the composite target. Meanwhile, the theory of molecular reaction dynamics, the particle collision software based on the Monte Carlo algorithm provided by Stopping and Range of Ions in Matter (SRIM), is used to simulate the collision of high-energy particles with air. The simulated results show that the electron stopping capability of air to high-energy nitrogen and oxygen atoms is far greater than the stopping capability of the nucleus; when the incident energy of high-energy particles is gradually increased, the blocking power of air to electrons increases first and then decreases. Also, the capability to stop the particles of the target nucleus is gradually reduced; under the condition of the implantation, the energy of nitrogen and oxygen atoms are both 1.8 MeV, the movement of the particles in the first seven layers of the target is relatively straight, and the phenomenon of deviation from the axis of symmetry is apparent in the silicon substrate. Due to the presence of more energy in the first seven layers of the target, it is not possible to see the more obvious lateral diffusion. The simulated results will provide a valuable reference for the prediction of single-event effects induced by ground-based pulsed laser simulating space high-energy particle irradiation.

Sub-picosecond single-pulse laser ablation of the CrMnFeCoNi high entropy alloy and comparison to stainless steel AISI 304

In recent years, high entropy alloy research has experienced increased interest and it was found that some of these materials have extraordinary properties. High entropy alloys also show an increased damage resistance to high-energy particle irradiation, mainly due to effects caused by the increased configuration entropy. So far, no detailed studies have been carried out regarding the interaction with high-energy electromagnetic radiation, particularly by means of lasers. In this work, we compare results of ultrashort-pulse laser-matter interaction of the CrMnFeCoNi alloy (Cantor alloy), the most researched representative of this material group, with the conventional alloy stainless steel AISI304. Since metals can in general be processed efficiently with ultrashort pulses, which is of particular interest for industrial applications, we performed our experiments with single infrared sub-picosecond pulses. The crater surface morphology and process energetics are discussed in detail and the validity of established ablation models is investigated. We find that the damage threshold of the CrMnFeCoNi alloy is slightly lower than that of AISI304 and consequently CrMnFeCoNi alloy shows an increased ablation volume. Therefore, the high entropy alloy CrMnFeCoNi can be processed efficiently with ultrashort-pulse lasers.

Grain-boundary plane orientation dependence of faceting–roughening transition in Au grain boundaries under electron-beam irradiation

Grain boundaries act to absorb and annihilate point defects generated by high-energy particles for polycrystalline nuclear materials. Thus, understanding the effect of irradiation of high-energy particles on the grain-boundary structural change is prerequisite to develop nuclear materials with desirable properties. It is expected that such an effect would be different for different GB characters. To explore the probability, we examine grain boundaries with twist and tilt components with the same misorientation relationship of [1 0 0]/45o in Au as a model system at a high-voltage transmission electron microscope with an acceleration voltage of 1250 keV. It is observed that, under the same irradiation condition, the tilt GB undergoes roughening while the twist one became faceted.

(Invited) Interfacial Engineering for High Voltage Performance of Perovskite Photovoltaic Cells

Since our first discovery of perovskite solar cell (PSC) in 2009, enormous efforts have been put into different aspects of PSCs and the progress has been incredibly fast on all fronts. The background, on-going R&Ds, and future direction of PSC research have been reported by our group as a comprehensive review.1 Although efficiency level has reached 25%, PSCs face serious challenges of practical stability and durability required for industrialization. Compositional engineering of lead halide perovskites by mixing different cations and anions, using modulator molecules and mixing 2D and 3D structures have improved the stability of perovskites against heat and moisture. However, organic cations in halide perovskites (methylammonium, etc.) and use of diffusible ionic dopants in hole transport materials (HTMs) are responsible for low stability of perovskites at high temperatures (>120oC). In this respect, use of all-inorganic perovskite materials and dopant-free HTMs is highly desired.2 We have conducted the device fabrication in this direction using CsPbI3 and CsPbI2Br as solution-processed perovskite films. The perovskite absorbers were made into junction with dopant-free HTMs to develop thermally stable PSCs.By chemical engineering to improve the quality of interfacial structure at the hetero-junction, all-inorganic and dopant-free PSCs yielded power conversion efficiency up to 15%. Further we could enhance the open-circuit voltage (Voc) of this PSC up to 1.42V, which is the highest Voc ever achieved with a single perovskite cell.3 In preparation of all-inorganic perovskites, a big challenge should also be directed to development of lead-free perovskite materials for environmental safety in practical applications.2 Among extensive applications of PSCs for outdoor and indoor power generation, use of PSCs in space environments is promising because thin perovskite photovoltaic films demonstrate high stability and tolerance against exposure to high energy particle irradiations (proton and electron beams).4 Thin absorbers (<500 nm) avoid accumulation of particles and due to intrinsic defect tolerant nature of perovskites, radiation-induced collision damage is highly suppressed. Our current efforts in making PSCs based on both lead and lead-free perovskites, and future perspectives of perovskite photovoltaics will be presented.

Numerical simulations of thermal conductivity in void-containing tungsten: Topological feature of voids

Tungsten, as a promising candidate for plasma-facing material in the advanced fusion reactors, has to suffer heat loading and high-energy particle irradiation. Since numerous voids form in the grain interior and on the grain boundary during irradiation, the thermal transfer capacity of tungsten would face a grand challenge. Herein, we systematically investigate the thermal conductivity of void-containing tungsten using finite element method. To understand the relation between the topological features of void and the corresponding thermal response within a wide temperature range, we analyze the thermal conductivity of tungsten by considering the arrangements, shapes and rotation angles of voids. The effects of intra- and inter-granular voids on the heat transmission are examined. The numerical results show how the thermal conductivity of single-crystal tungsten can be independent of void distribution pattern and how the void shape can lead to an anisotropic effective thermal conductivity. The predicted thermal conductivities are compared with those of well-known models and experimental data. Apart from voids, the proportion of grain boundary is also considered to analyze its effect on the thermal resistivity. Finally, we show how the spatial distribution of voids influences the heat flow inside the crystalline phase and across the grain boundary.