Radiation Defects Research Articles

Evolution of Irradiation Defects in W and W-Re Systems: A Density Functional Theory and Rate Theory Study

In a fusion environment, tungsten, a plasma-facing material in a reactor, is subject to the irradiation of high-energy neutrons, generating a large amount of displacement damage and transmutation products (such as rhenium, Re). We studied the evolution of defects under irradiation in W and W-Re systems using the density functional theory (DFT) and rate theory (RT) method. The results indicate that the evolution of irradiation defects is mainly affected by the irradiation dose, dose rate, and temperature. During irradiation, loops form first in W, followed by the generation of voids, which are due to the different migration energies of point defects. Higher dose rates result in a higher density and larger size of defects in tungsten. Higher temperatures cause a decrease in void density and an increase in size. The results obtained at 600 °C were in good agreement with the reported TEM data. In W-Re alloys, it is indicated that the formation of loops is delayed because Re suppresses the nucleation of loops. The dynamic introduction of Re in W stabilizes the growth of defects compared to W-Re alloys, suggesting that transmuting elements have less detrimental effects on irradiation than alloying. As defect densities and sizes were quantified under different irradiation conditions, the results provide data for the multi-scale simulation of the radiation damage and thermal/mechanical properties in plasma-facing materials under fusion conditions.

Separation in Fe–Ni and Fe–Ni–P alloys under electron irradiation and isochronous annealing

The annealing of radiation defects in the Fe–34.7at.%Ni and Fe–34.6at.%Ni–0.1at.%P alloys irradiated with 5 MeV electrons is studied by the method of residual electrical resistivity. It is shown that, during annealing after irradiation at 80 K, vacancies become mobile in the region of 220 K with a migration energy of about 0.6 eV. In this case, vacancy-impurity complexes (clusters) are formed, and in the H36 alloy vacancy clusters are formed. Under irradiation at room temperatures, vacancy defects accumulate in the form of vacancy clusters. The dissociation of these clusters at 350–550 K results in the appearance of freely migrating vacancies and enhanced self-diffusion. This leads to radiation-accelerated ordering processes in the Fe–Ni and Fe–Ni–P alloys. At temperatures around 800 K, homogenization of the solid solution occurs. The details and stages of the dissociation of vacancy-impurity complexes are discussed.

Formation of Radiation Defects in Wide-Band Semiconductors Based on Gallium (Ga2O3, GaN) under Proton Irradiation

Formation of Radiation Defects in Wide-Band Semiconductors Based on Gallium (Ga2O3, GaN) under Proton Irradiation

Shrinkage and coalescence behavior of helium bubbles in Fe9Cr1.5W0.4Si F/M steel under the coupling effect of compression stress and temperature

As important irradiation defects, helium bubbles will threaten the stability and reliability of reactor structural materials. Extensive research has been conducted on the dynamic response of helium bubbles under thermal annealing, irradiation, or tension, but the behavior and mechanisms of helium bubble evolution under compression remain to be understood. Here, by adopting in-situ cyclic nanocompression testing on Fe9Cr1.5W0.4Si F/M steel containing helium bubbles at 673 K, we present direct experimental evidence for the shrinkage and coalescence behavior of helium bubbles under the coupling effect of compression stress and temperature for the first time. Unlike the stress-free condition where the bubble size shows an increasing trend, compressive stress causes the bubble to shrink. Moreover, the large-sized bubbles show a greater change in size than small-sized bubbles. At 673 K, there is no thermal motion of the bubbles in F/M steel, and it is the deformation and mutual squeezing of bubbles under compression that causes the coalescence of tightly arranged bubbles. Furthermore, helium bubbles can act as dislocation sources to emit dislocations under compression, and the emitted dislocations can in turn envelope around the helium bubbles, thus hindering bubble coalescence and leading to the formation of deformed bubbles.

Analysis of the Effect of Radiation Defects by Low-energy Protons on Electrophysical Properties of Silicon N+ -P-P+Structure

Nowadays, radiation engineering is a promising direction in the creation of semiconductor devices. The proton irradiation is used to controllably change the optical, electrical, recombination, mechanical and structural properties of the semiconductors. Low-energy protons make it possible to purposefully change material properties near the surface where the n+ -p junction is located. In this paper, the impact of low-energy protons on the electro physical parameters of n+ -p-p+ silicon photoelectric converters (SPC) is analyzed. The current-voltage characteristics and switching time of these SPCs are measured. The switching time is determined using rectangular bipolar voltage pulses with an amplitude of 10 mV, a frequency of 200 kHz, or a frequency of 1 MHz. A theoretical and experimental analysis of the obtained results is performed. The comparison of experimental data with the results of calculations shows that protons with an energy of 180 keV and a dose of 1015 cm–2 create two regions in the space charge region of the n+ -p junction with different switching times of 4.2 × 10–7 s and 5.5 × 10–8 s. SPC frequency characteristics have been improved by reducing the effective lifetime by 5-10 times. This effect can be used to create high-speed photodiodes with an operating modulation frequency of 18 MHz.

Towards a reliable nanohardness-dose correlation of ion-irradiated materials from nanoindentation tests: A case study in proton-irradiated vanadium

Nanoindentation has been commonly used for evaluating the hardening effects of ion-irradiated materials. Nonetheless, establishing a reliable correlation between the hardness and irradiation dose is never trivial, due to not only the intrinsic analytical challenges of this technique, such as size effects, pile-up effects, etc., but also the fact that the irradiation dose is usually uneven inside the stress volume under the indenter, especially near the depth of dose peak. In the present work, the hardening in pure V irradiated with 1 MeV proton at various fluences is investigated by using nanoindentation tests, combined with the characterization of both irradiation defects and dislocations of the indented material. Under the cross-sectional indentation, we demonstrate that the nanohardness-dose correlation can be unified from the samples irradiated to different fluences and at different depths on each sample, as long as the lateral spanning of indenter is carefully considered. Crystal-plasticity finite-element-modeling simulation results can well describe the measured hardening-dose correlation, as well as the observed features on the change in strained fields and pile-up effects after irradiations. Moreover, the measured hardness is further corrected for the dose-dependent pile-up based on the surface profiling, and the indentation size effects based on surface indentation tests for deeper indentation depth, to reach a reliable connection between the hardening effects and the irradiation dose. Furthermore, microstructural characterization of the indented materials shows the pinning of dislocation by irradiation defects and the sweeping of those defects during dislocation migration. Molecular dynamics results suggest that the drag of loops by edge dislocations might cause the annihilation or aggregation of small loops, which could be responsible for the lower density but the larger size of irradiation loops in the strained region.

Micro/nano mechanical properties differences of shallow irradiation damage layer revealed by a combined experimental and MD study

Micropillar compression and nanoindentation techniques are both adopted to measure the mechanical properties in multi-energy He ion-irradiated Ni-based samples to study their relationship, and a distinct variation is observed. TEM characterization of the microstructure evolution and calculations based on the DBH model indicate that irradiation defects are not responsible for the observed variation. Subsequently, a comparative analysis of these two methods is simulated and their mechanisms are investigated using MD. Several factors, including activation of various slip systems, plastic area, and surface absorption, account for the differences observed in indentation and pillar compression tests, leading to the distinct evolution of internal initial dislocation lines, which significantly contribute to additional hardening in indentation tests.

Tuning the physiochemical properties of polycaprolactone-hydroxyapatite composite films by gamma irradiation for biomedical applications

Physiochemical properties of polycaprolactone-hydroxyapatite (PCL-HAp) composites were investigated in the pristine and after irradiation of γ rays (25, 50, 75, and 100 kGy). PCL-HAp composites were synthesized by solvent evaporation and characterized using spectroscopic methods as well as biological assays. The surface roughness (RMS) of the irradiated composite film (at 75 kGy) was 80 times higher than that of the pristine. Irradiation tailors the contact angle of the films from 77° to 90° (at 100 kGy). A decrease in particle size (at 100 kGy) of HAp nanorods in PCL-HAp composites film was observed. The XRD peak of PCL was slightly shifted from 21.2° to 21.7° (at 100 kGy) with the decrease in crystallite size. The peak intensity of the PCL and HAp altered on irradiation that was confirmed by FTIR and Raman analysis. Further, the bandgap of the irradiated film was lowered by 13 % (at 25 kGy). The luminescence intensity decreased due to the non-radiative process induced by the irradiation defects. All the samples possess hemocompatibility percentage of <10 % as per ASTM standards. At 75 kGy, fibroblast cell proliferation was higher than the pristine and other doses. The gamma-irradiated PCL-HAp composite films are potential candidates for tissue engineering applications.

Electrophysical parameters of p-i-n photodiodes, irradiated with 60Co γ-quanta

The results of studies of changes in the electrical parameters of p-i-n photodiodes manufactured on monocrystalline silicon wafers of p-type conductivity orientation (100) with ρ = 1000 Ohm cm, when irradiated with γ-quanta from a 60Co source, are presented. It has been established that as a result of irradiation of p-i-n photodiodes with doses up to 2·1015 quanta/cm2, the reverse dark current increases by more than an order of magnitude. However, the shape of the curve of the dependence of the current on the applied reverse voltage of irradiated p-i-n photodiodes does not change qualitatively, as for the original devices there are three regions with different dependences of current on voltage: sublinear, superlinear and linear, due to different mechanisms of generation-recombination processes in the depletion region of the p-n junction. The main reason for the increase in the reverse current of p-i-n photodiodes as a result of irradiation with γ-quanta is the formation of generation-recombination centers of radiation origin due to the condensation of primary radiation defects (vacancies and/or self-interstitial atoms) on technological residual structural defects formed during the growth of silicon single crystals, and during subsequent high-temperature treatments during the formation of devices.

GEOCHEMICAL VIEW ON “INOFFENSIVE” DEPLETED URANIUM

The interaction of alpha radiation from UO2 micro- and nanoparticles (uraninite) with the substance was visualized using alpha-autoradiography data on A-2 thick-layer nuclear photographic emulsions. The spherical area of action of alpha particles around UO2 micrograins, up to 100 microns in size, is a deeply transformed substance with a high density of radiation defects. The translation of these results on a living organism leads to the conclusion about the specific type of impact of micro- and nanoparticles of depleted uranium, in which prolonged internal irradiation in small doses of the whole organism is combined with catastrophically high doses of alpha radiation in local zones, near micro- and nanoparticles UO2.

Effects of Structural Radiation Disorder in the Near-Surface Layer of Alloys Based on NbTiVZr Compounds Depending on the Variation of Alloy Components

This research investigated how changes in the composition of Nb–Ti–V–Zr-based alloys affect their resistance to radiation damage and the preservation of strength characteristics when exposed to the heavy ions Kr15+ and Xe23+. These heavy ions simulate the impact of nuclear fuel fission fragments on the material. The primary objective of this study was to explore how variations in alloy components influence radiation resistance and the retention of alloy strength properties. Accumulation of radiation defects can potentially lead to embrittlement and a decrease in resistance to external factors during operation. An analysis of the X-ray diffraction data obtained from the initial alloy samples, in relation to the variations in the number of components, revealed that an increase in the number of components leads to the formation of a denser crystal structure. Additionally, this resulted in the emergence of a dislocation strengthening factor associated with changes in crystallite size. Concurrently, when assessing changes in the strength characteristics of the irradiated alloys, it was observed that the NbTiV and NbTiVZr alloys demonstrated the highest resistance to strength property degradation, specifically a 2.5- to 5-fold increase in resistance against a significant decrease in hardness. It was confirmed that the significant factor contributing towards the enhancement and preservation of the structural and strength properties is the dislocation strengthening mechanism. An increase in dislocation strengthening effectively enhances resistance against destructive embrittlement, particularly when exposed to high-dose irradiation.

Analysis of radiation defects in gallium nitride using deep level transient spectra and first principles methods

Radiation defects in gallium nitride devices were analyzed by combining experiments with simulation methods. Various forms of native defects, impurities, and these hydrogenated defect complexes in GaN were studied with first-principles calculations employing hybrid functionals which exhibit a reference data base for experimental analysis. We consider hydrogen complexes made of the combinations of single point defects (VGa, VN), di-vacancies (VGa-VGa, VN-VN, VGa-VN) and impurities (C, O, Si). Formation energies were computed for configurations with different charge states after full geometry optimizations. From the calculated formation energies, thermodynamic transition levels were evaluated, which are related to the thermal activation energies observed in experimental techniques such as deep level transient spectroscopy (DLTS). Hydrogen interstitial atoms were identified by the combination of DLTS and first-principles calculations. The transition level measured by DLTS was EC-0.5 eV, which is consistent with the calculation value. The signal of EC-0.9 eV peak in DLTS may be consisting of [VGa]-3/-2 and [VN-VN]+1/+2. According to the degradation of the electrical performance of the AlGaN/GaN high electron mobility transistors and the calculation results, the hydrogen passivation may be caused by [VGa]-3, [VGa-VGa]-2 and [VGa-VN]-1.

Molecular dynamics study of primary radiation damage in TiVTa concentrated solid-solution alloy

The primary radiation damage in pure V and TiVTa concentrated solid-solution alloy (CSA) was studied using a molecular dynamics method. We have performed displacement cascade simulations to explore the generation and evolution behavior of irradiation defects. The results demonstrate that the defect accumulation and agglomeration in TiVTa CSA are significantly suppressed compared to pure V. The peak value of Frenkel pairs during cascade collisions in TiVTa CSA is much higher than that in pure V due to the lower formation energy of point defects. Meanwhile, the longer lifetime of the thermal spike relaxation and slow energy dissipation capability of TiVTa CSA can facilitate the recombination of point defects. The defect agglomeration rate in TiVTa CSA is much lower due to the lower binding energy of interstitial clusters and reduced interstitial diffusivity. Furthermore, the occurrence probability of dislocation loops in TiVTa CSA is lower than that in pure V. The reduction in primary radiation damage may enhance the radiation resistance of TiVTa CSA, and the improved radiation tolerance is primarily attributed to the relaxation stage and long-term defect evolution rather than the ballistic stage. These results can provide fundamental insights into irradiation-induced defects evolution in refractory CSAs.

Insights on the capabilities and improvement ability of classical many-body potentials: Application to [formula omitted]-zirconium

Classical many-body potentials that have a rather low number of parameters and are based on physically-inspired functional forms are expected to display a reasonable transferability, though their flexibility is limited. Ways to improve them when their transferability is unsatisfactory and when new interesting structures/targeted properties emerge are not clearly established. Here, model screening and sensitivity analysis techniques are combined to get insights on the intrinsic capabilities of classical potentials for typical sets of targeted properties, and we propose to use the outcomes of the sensitivity analysis to improve potential performances. Usefulness is illustrated on existing simple second moment potentials (SMA), and we refit one such model for the study of small irradiation defects in α-zirconium. Application of this approach is recommended for more complex interaction models with up to tens of parameters, such as other classical many-body potentials or tight-binding electronic structure models, that are possible to re-optimize while gaining a better understanding of the role of their parameters.

Radiation Defect Formation in a Silicon Carbide Betaconverter

Radiation Defect Formation in a Silicon Carbide Betaconverter

A refined numerical simulation approach to assess the neutron irradiation effect on the mechanical behavior of wurtzite GaN

Neutron irradiation often produces distinct types of damage or defects in gallium nitride (GaN) materials, which could alter the mechanical properties of GaN. This work develops a numerical approach utilizing molecular dynamics (MD) simulation to capture the structural changes and defect evolution characteristics of wurtzite GaN under long-term low-dose neutron irradiation, and to evaluate the variations in fundamental mechanical properties. By comparing different types of potential functions available for describing GaN materials, the Tersoff/ZBL potential energy function is found to be more suitable for describing the irradiation effects of GaN. A method of using multiple recoil atoms to trigger cascade collision together with a three-stage irradiation process description is proposed to achieve an effective distribution of irradiation defects, as well as to improve computational efficiency. To simulate the irradiation damage accumulation due to successive cascade collisions, it is applicable to apply an iterative process for the simulation model. Using these approaches, uniaxial tension simulations for irradiated wurtzite GaN are performed to analyze the variations in its fundamental mechanical properties along [1 0 1¯ 0] crystalline direction. The results indicate that low-dose irradiation tends to decrease the Young's modulus and tensile strength of wurtzite GaN material, and could alter its deformation mechanisms to some extent.

Application of non-destructive geophysical methods for testing concrete structures

Non-destructive testing of reinforced concrete structures is of utmost importance in construction and civil engineering, where many factors can cause internal and external deterioration of reinforced concrete structures: the environment, nuclear radiation, and structural defects, among others. Geophysical non-destructive testing methods such as ultrasonic and radar have been increasingly used in civil engineering in recent years. Improvements in the ultrasonic testing of concrete have produced detailed images of the interiors of even the most complex structures and allowed for the earliest possible detection of deterioration. In this study, three geophysical methods were applied to inspect concrete structures: parallel seismic, sonic echo, and ultra-seismic. These three testing methods are applied to concrete foundations of two depths, namely 5, and 7 m; the deep foundation has a fracture at a depth of 4.5 m. The collected data are processed using a low-pass filter to remove the higher frequencies. These results of parallel seismic tests accurately predict foundation depths of 5.0 and 6.6 m and P-wave velocities of 2551 and 1097 m/s, respectively. Sonic echo tests yield depth predictions of 5.07 and 7.01 m for the tested foundations and 4.44 m for the depth of the crack. Meanwhile, ultra-seismic tests give depth predictions of 7.1 and 4.6 m for the foundation and fracture, respectively, while clarifying the P-wave velocities of the corresponding reflections: 3447 m/s exiting the 7-m foundation and 2668 m/s exiting the embedded fracture. Depth estimates based on each method show strong agreement with true depths. In conclusion, these three geophysical methods have great potential to provide quantitative data to drive quality assurance and remediation for concrete structures.

The role of various permutations of TiO2 and MoS2 nanolayers on the radiation tolerance of Cu-TMD and Cu-TMO nanocomposites

Cu-based nanocomposites (NCs) are expected to have high radiation tolerance. Here we focus on using titanium dioxide (TiO2) and molybdenum disulphide (MoS2) to investigate interactions of interface of Cu- transition metal dilucogenides (TMD) and Cu- transition metal oxide (TMO) NCs which have been called Cu-2D material NCs. We generate six configurations of NCs including Cu/ TiO2/Cu (Sample1), Cu/TiO2@Cu@TiO2/Cu (Sample2), Cu/TiO2@Cu@MoS2/Cu (Sample3), Cu/MoS2@Cu@TiO2/Cu (Sample4), Cu/MoS2@Cu@MoS2/Cu (Sample5), and Cu/ MoS2TiO2/Cu (Sample6) to suggest the best model for improving the radiation tolerance of Cu-2D material NCs. The irradiation tolerance simulations have been carried out under a collision cascade induced by 6 keV primary knock-on atom (PKA) by atomistic simulations. Results imply the radiation tolerance of the Sample4 and Sample5 NCs is higher than that of other studied NCs. In order to clarify the sink action of the interface of these two NCs, we evaluated radiation defects and thermodynamics properties of this region at 3, 6, and 9 keV PKA energy. The dissipated potential energy in Cu layers of the Sample4 interface is significantly higher than that of Sample5 interface for 6 and 9 keV of PKA energy. The results of energetic calculations indicate the defect formation energy is reduced in the vicinity of interfaces. Compared with the Sample4, the Sample5 has low segregation energy for the interstitial emission mechanism to annihilate vacancies. Also, the interface of Sample5 has a higher strength of interaction and attraction with vacancies due to the low value of vacancy formation energy (Evac).

Introduction Rates of Electrically Active Radiation Defects in Proton Irradiated n-Type and p-Type Si Monocrystals

Introduction Rates of Electrically Active Radiation Defects in Proton Irradiated n-Type and p-Type Si Monocrystals

Chemical and topological disordering in M23C6 due to irradiation: An atomic-scale observation

To clarify the stability of M23C6 precipitate in steels under irradiation, the chemical and topological disordering behaviors in M23C6 subjected to ion irradiation at elevated temperatures were investigated with the combined application of high-resolution electron microscopy (HREM) and electron energy-loss spectroscopy (EELS). Results show that the duplex structured M23C6 which is the core-crystalline and shell-amorphous was observed in the specimen irradiated at 623 K, nevertheless, no amorphous phase was observed in the specimen irradiated at 673 K. HREM observation confirmed the occurrence of the chemical disordering in irradiated M23C6, and the disordering of W atoms in the M23C6 unit cell was clarified by the peak intensity profile of the atomic column from the HREM image. EELS analyses indicate that no obvious chemical shift was observed by the core-loss spectrum, however, the change in the electron mean free path (λ) due to irradiation was confirmed by the low-loss spectrum, which is related to the formation of both irradiation defects and amorphous phase. It is proposed that the decreased material density upon irradiation is ascribed to the formation of W-vacancy-dominated defect clusters. An obvious change in interatomic distance was not observed in the irradiated M23C6 based on the radical distribution function analysis by extended energy-loss fine structure spectrum. However, the peak intensity decreased by irradiation, confirming the occurrence of chemical and topological disordering, regardless of the carbide being crystalline or amorphous.