Radiation-induced Defects Research Articles

The evolution of radiation-induced point defects near symmetrical tilt Σ5 (3 1 0) 〈0 0 1〉 grain boundary in Ga stabilised δ-Pu: A molecular dynamics study

Molecular dynamics (MD) simulations were performed to investigate the evolution of radiation-induced point defects affected by the symmetrical tilt Σ5 (310) 〈001〉 grain boundary (GB) in Ga stabilised δ-Pu. From the perspective of formation energy, the formation energy of vacancies had no prominent change in the whole region, but it was lower than the formation energy of interstitial atoms. The formation energy of interstitial atoms near GB was lower than that in the bulk. On the other hand, the average formation energy of interstitial Pu atoms was greater than that of interstitial Ga atoms. Furthermore, by comparing the evolution of radiation-induced point defects when primary knock-on atom (PKA) was located at −25 Å and 25 Å far from the GB, respectively, and analyzing the tendency of the number of remaining defects with the distance between PKA and GB changing, it could be found that interstitial atoms were more easily trapped in Σ5 (310) 〈001〉 GB than vacancies for Pu-Ga alloy. Simultaneously, the influence of temperature on the number of point defects near GB was taken into consideration, and the results displayed that the number of residual point defects in Pu-Ga alloy with Σ5 (310) 〈001〉 GB showed a decreasing trend with temperature increasing because temperature had an effect on the diffusion of point defects. Remaining interstitial atoms rather than remaining vacancies, moreover, are more severely affected by temperature, for interstitial atoms were more easily absorbed by GB.

Irradiation-Induced Defects and Their Effects on the Electronic Structures in T-Carbon

Irradiation-Induced Defects and Their Effects on the Electronic Structures in T-Carbon

Prenatal Radiation Exposure Leads to Higher-Order Telencephalic Dysfunctions in Adult Mice That Coincide with Reduced Synaptic Plasticity and Cerebral Hypersynchrony.

Higher-order telencephalic circuitry has been suggested to be especially vulnerable to irradiation or other developmentally toxic impact. This report details the adult effects of prenatal irradiation at a sensitive time point on clinically relevant brain functions controlled by telencephalic regions, hippocampus (HPC), and prefrontal cortex (PFC). Pregnant C57Bl6/J mice were whole-body irradiated at embryonic day 11 (start of neurogenesis) with X-ray intensities of 0.0, 0.5, or 1.0 Gy. Female offspring completed a broad test battery of HPC-/PFC-controlled tasks that included cognitive performance, fear extinction, exploratory, and depression-like behaviors. We examined neural functions that are mechanistically related to these behavioral and cognitive changes, such as hippocampal field potentials and long-term potentiation, functional brain connectivity (by resting-state functional magnetic resonance imaging), and expression of HPC vesicular neurotransmitter transporters (by immunohistochemical quantification). Prenatally exposed mice displayed several higher-order dysfunctions, such as decreased nychthemeral activity, working memory defects, delayed extinction of threat-evoked response suppression as well as indications of perseverative behavior. Electrophysiological examination indicated impaired hippocampal synaptic plasticity. Prenatal irradiation also induced cerebral hypersynchrony and increased the number of glutamatergic HPC terminals. These changes in brain connectivity and plasticity could mechanistically underlie the irradiation-induced defects in higher telencephalic functions.

Enhancing the phase stability of TiNi intermetallic compound via nanocrystallization in an irradiated multicomponent vanadium alloy

Intermetallic compounds often have a low radiation tolerance due to the low recombination rate of radiation-induced defects. In the present work, we designed a novel multicomponent vanadium-based alloy (MVA), V34Ti25Cr10Ni30Pd1, containing a micron-scale TiNi matrix phase with VCr nanoprecipitates (NPs) and a micron-scale VCr matrix phase with TiNi NPs. The MVA was irradiated with 6 MeV Ti3+ ions with a radiation dose of 5×1015ions/cm2 at room temperature. Results indicated that the micron-scale intermetallic TiNi matrix along with VCr NPs inside both became amorphous, while the micron-scale VCr matrix including numerous intermetallic TiNi NPs both exhibited a high structural stability after ion irradiation. The intermetallic TiNi matrix becomes amorphous due to the accumulation of radiation-induced defects, and the intermetallic TiNi NPs in VCr matrix have a high stability of crystallographic structure due to high-density interfaces between NPs and matrix. These results indicate that the phase stability of TiNi intermetallic compound is increased after nanocrystallization. Besides, the discrepancy of two matrix phases including precipitates after ion irradiation, and the underlying mechanisms are discussed in detail in this work. This work gives a guidance for designing new vanadium alloys and intermetallic compounds with enhanced structural stability under ion irradiation.

Effects of helium bubbles on deformation of aluminum matrix

Helium bubble influence on the deformation of aluminum is investigated via simultaneous electron backscatter diffraction and digital image correlation (DIC) during in situ tensile and compressive tests . The majority of helium is generated through the transmutation reaction 10 B(n, α ) 7 Li under neutron irradiation , which is carried out at 40 ∘ C to ∼ 0.3 dpa. The mesoscale deformation behaviors of aluminum matrix with and without helium bubbles are compared, and the interactions between helium bubbles and slip bands are analyzed. Helium bubbles along with other types of irradiation-induced defects (like dislocation loops and black dots) harden significantly the aluminum matrix around second-phase AlB 2 particles. Slip bands cannot penetrate the areas with high-density irradiation-induced defects. They bypass such areas through cross slip, exhibiting slip band deflection. Transmission electron microscopy on irradiated materials after deformation reveals abundant helium bubbles, dislocations, dislocation loops and black dots around AlB 2 particles, due to complex interactions between irradiation-induced defects with dislocations. Helium bubbles together with other types of irradiation-induced defects have pinning effects on dislocations, and pressurized helium bubbles may also punch out dislocation loops. The multiscale analyses demonstrate the helium bubble-dominated hardening.

Post-irradiation microstructural examination of EUROFER-ODS steel irradiated at 300°C and 400°C

The effect of neutron irradiation on the microstructure of EUROFER-ODS alloy reinforced with an addition of 0.5% Y 2 O 3 was analyzed by transmission electron microscopy . The irradiation of up to 16.2 dpa damage dose at 300°C and 400°C was performed in Petten High Flux Reactor. This study focuses on the imaging, identification, and quantitative analysis of interstitial loops and voids located on ODS particles. The nano-sized loops and point defects with b½〈111〉 Burgers vectors are preferentially located near structural defects such as the line dislocations or impurities in the material irradiated at 300°C. Homogeneously distributed loops having Burgers vectors of b½〈111〉 and b〈100〉 types were found in the material irradiated at 400°C. The obtained quantitative data on radiation-induced defects such as size, number density and relaxation volume were compared with EUROFER97 irradiated at the same conditions. It was found that the occurrence of radiation induced defects depends on the local number density and the size distribution of the ODS particles and not only on the irradiation damage and temperature.

Investigating radiation-induced segregation on intragranular defects in a 316L(N)

Radiation induced segregation (RIS) on lattice defects and phase stability under irradiation have been investigated in an optimized solution annealed 316L(N) with an increased content of N and a significant amount of Nb. Primary Z-phase nitrides were observed within the as-received microstructure. 5 MeV Fe3+ ion irradiation was conducted at 450 °C up to 1dpa. Post-ion irradiation characterization was performed via nanoscale techniques coupling and correlation to associate radiation induced defects such as cavities and dislocation loops to the local chemistry. Cr, Fe and Ni observed RIS trends were expected, but P was solely measured at the vicinity of cavities. Void-precipitate association has been detected thanks to transmission electron microscopy (TEM) and it is believed to explain the low reduced atomic density measured at the location of a feature within an atom probe tomography (APT) volume. Nb-rich novel features were observed after irradiation and first results are brought to establish a link between these features and the primary Z-phase.

Prediction of hardening effect by irradiation-induced vacancy clusters with dislocation dynamics

Development of irradiation hardening models attracts extensive attention in designing nuclear materials. Dislocation dynamics (DD) method is a powerful tool in this field for its advantages of predicting mechanical response with microstructural changes such as dislocation evolution, and its extendibility by incorporating the hardening mechanisms, i.e., the dislocation motion impeded by irradiation-induced defects such as vacancy/interstitial clusters, dislocation loops, precipitates etc. Focusing on the hardening effect contributed by vacancy cluster (VC) that is of high number density even at low irradiation dose, this work develops a VC-dislocation interaction model based on Eshelby's equivalent inclusion method. Specifically, a VC is treated as an inclusion with a certain eigenstrain that gives zero stress inside the VC at the presence of dislocation. By adding the interaction force between VC and dislocation derived using the eigenstrain to dislocation force, we implement this model in open-source DD software ParaDiS. Further, we apply the model to investigate the hardening effect by VCs with varying size and number density. Simulation results show that the hardening by VCs of different sizes is all proportional to the 2/3 power of total number density. To further quantify the hardening effect of VCs, we propose a hardening model which modifies the previous Frediel-Kroupa-Hirsch (FKH) model by making the hardening coefficient in linear relation with VC diameter and introducing an effective diameter that account for size distribution of VCs. The MFKH (modified FKH) model with no free parameter shows good accuracy in predicting VC induced hardening in tungsten comparing with experiments.

Impact of defects on the structural and electrical transport properties of Sb2Te3 thin films by SHI irradiation

Implantation of defects is an attractive trend for the modification of important properties of thin films for practical applications. In the present attempt, an effective approach for tuning the native defects in thin films is reported. The films were sequentially irradiated at five different fluences (5 × 1011, 1 × 1012, 3 × 1012, 5 × 1012, and 1 × 1013 ions/cm2). The key role of high-energy Ni ion irradiation-induced native defects was observed by the modifications in the physical properties of samples. However, irradiation induces a structural phase transition through strain. The average crystallite size as determined from X-ray diffraction (XRD) peak broadening was found to be 19.3 ± 5 (nm). A monotonic increase in the lattice strain was observed up to a fluence of 5 × 1012 ions/cm2. The resistivity v/s temperature measurements revealed an increase in resistivity up to the fluence 3 × 1012 ions/cm2 indicating an increase in grain boundaries effect. Our findings provide an insight into the correlation of tuned properties with the defects induced by irradiation and also a route to have the defects in a precise and controlled way.

M-Center in Neutron-Irradiated 4H-SiC

We report on the metastable defects introduced in the n-type 4H-SiC material by epithermal and fast neutron irradiation. The epithermal and fast neutron irradiation defects in 4H-SiC are much less explored compared to electron or proton irradiation-induced defects. In addition to the carbon vacancy (Vc), silicon vacancy (Vsi) and carbon antisite-carbon vacancy (CAV) complex, the neutron irradiation has introduced four deep-level defects, all arising from the metastable defect, the M-center. The metastable deep-level defects were investigated by deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and isothermal DLTS. The existence of the fourth deep-level defect, M4, recently observed in ion-implanted 4H-SiC, has been additionally confirmed in neutron-irradiated samples. The isothermal DLTS technique has been proven as a useful tool for studying the metastable defects.

Structural and Optical Modifications in the BaO-ZnO-LiF-B2O3-Yb2O3 Glass System after γ-Irradiation.

A Yb3+-doped borate glass system was examined for the structural and optical modifications after -irradiation. Among the studied 10BaO-20ZnO-20LiF-(50-x)B2O3-xYb2O3 (x = 0.1, 0.5, 0.7, and 1.0 mol%) glasses, the 10BaO-20ZnO-20LiF-49.9B2O3-0.1Yb2O3 glass showed the highest thermoluminescence intensity, trap density, and trap depth. The glass was irradiated with the optimum -dose of 1 kGy towards the analysis of radiation-induced defects. The amorphous nature was preserved before and after irradiation. The glass density slightly increased after irradiation. The structural rearrangement was evident from the Fourier transform infrared spectroscopy by the appearance and disappearance of some bonds after -irradiation. The transformation of [BO4] units into [BO3] units and non-bridging oxygens was deduced. The color of the glass darkened after irradiation and the optical absorption intensity enhanced between 250 and 700 nm. The optical bandgap reduced and Urbach energy increased upon -dose exposure. The electron spin resonance of the irradiated glass exhibited two signals at g = 2.0167 and g = 1.9938, corresponding to the non-bridging oxygen hole center and Boron E’-center, respectively.

Molecular dynamics simulation of vacancy and void effects on strain-induced martensitic transformations in Fe-50 at.% Ni model concentrated solid solution alloy

Strain-induced martensitic transformations can improve the strength and ductility of some face centered cubic (FCC) metals and alloys. Irradiation-induced defects such as vacancies, dislocation loops, and voids activate martensitic transformations over a wider range of mechanical loading conditions than in pristine material. However, the mechanisms underlying irradiation-enabled martensite transformations remain unclear. In this work, we use molecular dynamics simulations to study the effect of vacancies and voids on strain-induced martensitic transformations in a model concentrated solid solution alloy Fe-50 at.% Ni. It has been found that single vacancies have no resolvable effect on the transformation because they reduce the stacking fault energy by a relatively insignificant margin and do so only if the vacancy is located on the stacking fault plane. Voids, however, activate the martensite transformation through shear strain accumulation around the void due to dislocation pileup. The larger the void, the more pronounced this effect.

Radiation damage and abnormal photoluminescence enhancement of multilayer MoS2 under neutron irradiation

In this work, neutron irradiation effects on the optical property of multilayer MoS2 have been investigated in depth. Our results display that the intensity of the photoluminescence (PL) spectra of MoS2 flakes tends to slightly decrease after exposed to neutron irradiation with low fluence of 4.0 × 108 n/cm2. An unexpected improvement of PL intensity, however, is observed when the irradiation fluence accumulates to 3.2 × 109 n/cm2. Combined with the experimental results and first-principles calculations, neutron irradiation damage effects of multilayer MoS2 are analyzed deeply. Sulfur vacancy (V S) is found to be responsible for the attenuation of the PL intensity as a major defect. In addition, our results reveal that the adsorbed hydroxyl groups (OH) and oxygen atoms (O) on the surface of MoS2 flakes not only promote the transition from trion excitons to neutral excitons, but also repair the V S in MoS2, both of which contribute to the enhancement of luminescence properties. The detailed evolution process of irradiation-induced defects is discussed to reveal the microscopic mechanism of the significantly difference in luminescence intensity of MoS2 under different irradiation stages. This work has great significance for evaluating the neutron radiation hardness of multilayer MoS2, which is helpful to enrich the fundamental research on neutron irradiation effects.

Effect of void morphology on void facilitated plasticity in irradiated Cu/Nb metallic nanolayered composites

Voids are common radiation-induced defects in nuclear materials and produce detrimental effects on mechanical properties. The influence of a pre-existing void on mechanical behavior has been investigated in single crystals, but the effects of void located at bimetal interfaces on the dislocation nucleation mechanisms and associated mechanical performance have not been fully studied. Using Cu/Nb metallic nanolayered composites (MNCs) as a model system, with atomic-scale simulations, we report on the influence of a pre-existing void at the Cu/Nb interface on dislocation nucleation and deformation behavior. Compared with the void-free system, the size, location and shape of the voids can influence dislocation behavior significantly, such as the initial nucleation site, the critical nucleation stress, and the preferred slip system. As the size of the faceted void increases from 3 to 4 nm, the dominant mechanism of dislocation nucleation changes from a misfit dislocation-assisted localized shear to a void edge-assisted Frank-Read-like mechanism. Also, the location of the faceted void can change the coupled strain field between the void and the misfit dislocation, ultimately affecting the preferred slip system selection. In contrast, the spherical void cannot effectively activate the Frank-Read-like dislocation source due to the absence of edges. This work reveals the effects of void morphology on dislocation behavior, and provides an explanation for co-dominated plasticity of bimetal interface and void.

Improving radiation-tolerance of bcc multi-principal element alloys by tailoring compositional heterogeneities

Molecular dynamic simulations were performed to investigate the displacement cascade process in refractory bcc complex concentrated alloys, including equi-atomic binary, ternary, and quaternary systems made of the elements Mo, Nb, Ta and W. Our simulation results show that more principal elements do not necessarily mean better radiation resistance. Instead, bcc binary MoNb and NbW CCAs, which have low binding energy of interstitial clusters, can also yield good resistance to the generation of radiation-induced defect clusters. At same time, MoNb also have low self-interstitial formation energy range, so there are more Frenkel Pairs than other bcc binary like MoTa and MoW although number of interstitials in clusters of MoNb is least. More importantly, we find the binding energy of interstitial clusters is highly tunable by changing elements combination and tailoring compositional heterogeneities (such as short-range ordering). Such strategies may pave the way for new design concepts of radiation-tolerant alloys.

Influence of α-particles irradiation on the properties and performance of silicon semiconductor detectors

Deterioration of the operation parameters of p-type Si surface-barrier detector and Si(Li) p-i-n detector upon irradiation by alpha-particles was investigated. The detectors were irradiated at room temperature up to a total number of the registered α-particles Nα equal to 6 × 109. Prolonged irradiation has resulted in a deterioration of the detectors energy resolution ability and it was found that the increase of α-peaks broadening can be described by a linear function of Nα with a slope Δσ/ΔNα ∼ (1.4–1.8) × 10–9 keV/α for both detectors. Resolution deterioration was associated with the increase of the detectors leakage current, which proceeds linearly with the number of absorbed α-particles with the slope ΔI/ΔNα ∼ (7-17) × 10-17 A/α. The increase of the detectors reverse current was related with appearance of radiation-induced defect level at 0.56 eV above the valence band.

Healing of nanocracks by collision cascades in nickel

We use molecular dynamics simulations to investigate the interaction between collision cascades and pre-existing nanocracks in nickel (Ni). We find that collision cascades cause the cracks to heal whenever a cascade initiates a thermal spike whose core overlaps with the crack. Moreover, crack healing affects the distribution of radiation-induced defects generated during a collision cascade: defect clusters, such as dislocations and stacking fault tetrahedra, dominate in the presence of crack healing, while isolated point defects dominate in its absence. This work indicates that irradiation may reduce the number of pre-existing crack-like flaws in metallic components, potentially improving their mechanical resilience.

Correlation between Structural Evolution and Device Performance of CH3NH3PbI3 Solar Cells under Proton Irradiation

Organic–inorganic hybrid perovskite has gained enormous attention due to its potential applications in next-generation space solar cells. Although the influence of particle irradiation on perovskite materials and devices has been studied, the correlation between the structural evolution of materials and device performance under irradiation deserves to be further clarified. Herein, the relationship between the structural damage and performance degradation of CH3NH3PbI3 (MAPbI3) solar cells under 50 keV proton irradiation up to 1 × 1015 p cm–2 has been revealed by means of comprehensive experimental characterization and defect simulation. MAPbI3 films and solar cells exhibited excellent tolerance to proton irradiation up to 1 × 1014 p cm–2. In contrast, due to the partial amorphization caused by the degradation of organic groups at a higher proton fluence of 1 × 1015 p cm–2, the photoluminescence spectrum of MAPbI3 films quenched, the carrier lifetime shortened from 57.8 to 17.6 ns, and the density of trap states increased from 8.32 × 1015 to 1.69 × 1016 cm–3. Coupled with the deactivation of the hole transport layer, MAPbI3-based solar cells become inoperative under high irradiation greater than 1 × 1014 p cm–2. In addition, the photovoltaic performance of solar cells showed a noticeable recovery phenomenon when the fluence was no more than 1 × 1014 p cm–2, which was attributed to the imbalance between irradiation-induced defect generation at a high incident rate and defect recombination at different locations. Our results predict that, compared to accelerated simulation experiments on the ground, perovskite materials served in actual space environments at the same fluence have better resistance to proton irradiation due to a low injection rate, thus proving their application prospect in space solar cells.

In-situ TEM investigations of dislocation loop annealing kinetics in neutron-irradiated 9%Cr RAFM steel

Post-irradiation annealing (PIA) is beneficial in recovering degraded mechanical properties of irradiated materials due to the evolution of irradiation-induced defects. To understand the underlying responsible mechanisms, isothermal PIA experiments were carried out in this work on a neutron-irradiated 9%Cr reduced-activation ferritic-martensitic steel (EUROFER97) using in-situ transmission electron microscopy. In general, PIA at 600 °C led to an appreciable reduction of the dislocation loop density and increment in the loops mean size. This is found mainly associated with the vacancy-mediated loops shrinkage phenomenon. The driving force for this process is loop's curvature force. Nevertheless, the spontaneous evolution of the loops neighboring microstructure substantially alters their annealing kinetics. Therefore, in this study, loops’ annealing kinetics in EUROFER97 is discussed in terms of various scenarios originating in terms of the presence or absence of the local external sources and sinks. In addition, influence of loops type, alloying elements segregation and free surface are also discussed.

Evidence for the formation of two types of oxygen interstitials in neutron-irradiated \u03b1-Al2O3 single crystals

Due to unique optical/mechanical properties and significant resistance to harsh radiation environments, corundum (α-Al2O3) is considered as a promising candidate material for windows and diagnostics in forthcoming fusion reactors. However, its properties are affected by radiation-induced (predominantly, by fast neutrons) structural defects. In this paper, we analyze thermal stability and recombination kinetics of primary Frenkel defects in anion sublattice − the F-type electronic centers and complementary oxygen interstitials in fast-neutron-irradiated corundum single crystals. Combining precisely measured thermal annealing kinetics for four types of primary radiation defects (neutral and charged Frenkel pairs) and the advanced model of chemical reactions, we have demonstrated for the first time a co-existence of the two types of interstitial defects – neutral O atoms and negatively charged O- ions (with attributed optical absorption bands peaked at energies of 6.5 eV and 5.6 eV, respectively). From detailed analysis of interrelated kinetics of four oxygen-related defects, we extracted their diffusion parameters (interstitials serve as mobile recombination partners) required for the future prediction of secondary defect-induced reactions and, eventually, material radiation tolerance.