Effect Of Neutron Irradiation Research Articles

Study on the changes in the reverse recovery characteristics of high-power thyristor under 14.1 MeV fusion neutron irradiation

When the d-T fusion reaction takes place in a Tokamak, the high-energy neutrons emitted, with an energy of 14.1 MeV, can alter the electrical properties of high-power thyristors in Quench Protection System (QPS). The Reverse Recovery Characteristics (RRC) of High-power Thyristor (HP-SCR) is one of the crucial issues affecting the reliability of QPS. In this paper, the change in the RRC of HP-SCR under 14.1 MeV neutron irradiation is deeply studied. Firstly, the microscopic material damage mechanism of HP-SCR induced by neutron irradiation and its relationship with RRC are deeply analyzed. Secondly, a highly efficient neutron irradiation experiment is designed and conducted to effectively validate the correctness of the theoretical analysis regarding changes in RRC. Finally, the effects of neutron irradiation on the QPS, consisting of multiple thyristors arranged in series, are analyzed and discussed through system-level simulations. The study offers important recommendations for the maintenance and upgrade of QPS, which will greatly enhance the safety of Tokamak devices.

EPR spectroscopic characterization of neutron-irradiated nanocrystalline anatase particles

This study investigates the effects of neutron irradiation on nanocrystalline anatase (TiO₂) using electron paramagnetic resonance (EPR) spectroscopy. Neutron irradiation doses of 1.6 × 101⁵, 8 × 101⁵, 4 × 101⁶, and 2 × 101⁷ n/cm2 were applied to TiO₂ samples, and changes in the EPR spectra were analyzed to explore the transmutation of titanium (Ti) atoms into vanadium (V). The results reveal that the irradiation induces the conversion of 50Ti to 51V via neutron capture, accompanied by the formation of oxygen and titanium vacancies. The intensity of the EPR signal decreases with increasing neutron dose, indicating that the formation of 51V isotopes and other irradiation-induced effects influence the material's paramagnetic behavior. The study provides insights into the transmutation process and highlights the potential of neutron irradiation for modifying the properties of TiO₂, with implications for photocatalytic applications and radiation-resistant materials.

Microstructure, electrical resistivity, and tensile properties of neutron-irradiated Cu–Cr–Nb–Zr

High strength, high conductivity copper alloys that can resist creep at high temperatures are one of the primary candidates for efficient heat exchangers in fusion reactors. Cu–Cr–Nb–Zr (CCNZ) alloys, which were designed to improve the strength and creep life of ITER Cu–Cr–Zr (CCZ) reference alloys, have been found to have comparable electrical conductivity and tensile properties to CCZ alloys. The measured creep rupture times for these improved alloys is about ten times higher than the ITER reference alloys at 90–125 MPa at 500 °C. However, the effects of neutron irradiation on these alloys, and the ensuing material properties, have not been studied; thus, their utility in a fusion reactor environment is not well understood. This study characterizes the room temperature mechanical and electrical properties of a neutron-irradiated CCNZ alloy and compares them to a neutron-irradiated ITER reference heat sink CCZ alloy. Tensile specimens were neutron irradiated in the High Flux Isotope Reactor (HFIR) to 5 dpa between 250 °C and 325 °C. Post-irradiation characterization included electrical resistivity measurements, hardness, and tensile tests. Microstructural evaluation used scanning electron microscopy, energy dispersive x-ray spectroscopy, and atom probe tomography to characterize the irradiation-produced changes in the microstructure and investigate the mechanistic processes leading to post-irradiation properties. Transmutation calculations were validated with composition measurements from atom probe data and used to calculate contributions to the increased electrical resistivity measured after irradiation. Comparisons with CCZ alloys in the same irradiation heat found that the post-irradiated CCNZ and CCZ alloys had comparable electrical resistivity. Although CCNZ alloys suffered more irradiation hardening than CCZ, the overall tensile behavior deviated very little from non-irradiated values in the temperature range studied.

Investigation of neutron irradiated W/CuCrZr joints

This study investigates the effects of neutron irradiation on tungsten (W) and copper-chromium-zirconium (CuCrZr) joints under conditions mimicking the high neutron flux environment of a tokamak fusion reactor. Samples of W/CuCrZr joints were subjected to irradiation in the Belgian Reactor 2 (BR2) nuclear reactor at SCK CEN (Belgian Nuclear Research Centre) to simulate the intense neutron exposure characteristic for International Thermonuclear Experimental Reactor (ITER) and DEMOnstration power plant reactor (DEMO) operations. The primary objective was to evaluate changes in the mechanical properties and microstructure of these materials, which are critical for their potential use in plasma-facing components.It is revealed that a significant reduction in tensile elongation of the joint, indicating some degree of embrittlement, is observed after the irradiation. Importantly, this effect is independent of the irradiation temperature. Possible physical reasons for the observed phenomenon are discussed.

Effects of neutron radiation on the thermal conductivity of highly oriented pyrolytic graphite

Effects of neutron radiation on the thermal conductivity of highly oriented pyrolytic graphite

Neutron irradiation induced transmuted Ga-doping of ZnO thin films: Structural and opto-electronic investigations

Metal oxide nanoparticles, particularly zinc oxide (ZnO) thin films, have significant applications in photocatalysis, non-volatile memories, resistive switching, energy conversion, and many more. This study examines the effects of neutron irradiation on ZnO thin films synthesized via a sol-gel and spin coating technique, subsequently annealed at 450 °C. The films are exposed to neutron radiation of various fluence rates. One of the major effects of neutron irradiation is the transmutation of zinc (Zn) into gallium (Ga), resulting in a Ga-doped ZnO thin film. Scanning electron microscopy (SEM) reveals morphological changes, including forming nano-scale structures on the surface, post-irradiation. Energy dispersive X-ray analysis (EDAX) identifies the transmutation of Zn to Ga. X-ray diffraction indicates a shift in the peaks due to radiation-induced defects. Optical studies show a blue shift in absorption spectra and an increase in bandgap from 3.1 eV to 3.2 eV after irradiation. Photoluminescence spectra exhibit intensified defect-related emissions. Electrical measurements via I-V and Hall techniques reveal reduced current and carrier concentrations with transmuted Ga-doped ZnO thin film. These findings highlight the significant impact of neutron irradiation on the structural, optical, and electrical properties of ZnO thin films, providing insights into their behaviour under space-like conditions.

The synergistic effect of neutron irradiation on the tensile properties of Fe-0.74 wt.% Ni alloy: A combined study of machine-learning and molecular dynamics

The aim of this study is to elucidate the mechanisms of irradiation damage to reactor pressure vessel (RPV) steel using a machine learning algorithms and high-throughput calculations. Various Fe-Ni alloy structures were generated based on structural enumeration for high-throughput first-principles calculations, with the Fe-Ni interatomic potential trained using a Gaussian approximation function. Simulations were conducted using LAMMPS software to investigate the effects of neutron irradiation on the tensile properties of Fe-0.74 wt.% Ni alloy, utilizing the well-established Fe-Ni interatomic potential. The irradiation dose significantly impacts defects in the Fe-Ni alloy. Synergistic effects of alloy solute element content and temperature with irradiation defects reveal that defect numbers at irradiation points increase linearly with MD-dpa and PKA energy. During irradiation, Ni atoms diffuse via the exchange with vacancy, synergizing with other Ni elements. Notably, Ni content inversely affects yield stress, resulting in lower yield stress in irradiated materials compared to pre-irradiation levels. While temperature inversely affects yield stress, its synergistic effect with defects increases yield stresses post-irradiation, known as irradiation hardening. Post-irradiation, the yield strain increases, and a flat plateau stress region is observed in Fe-Ni alloys. Ni atoms act as a buffer during the stretching process, contributing to a relatively gentle slope stress region despite increasing stress. The distribution of Ni atoms significantly influences the stress-strain curve, in which the aggregated Ni atoms decrease yield strength, whereas uniform distribution increases it, highlighting Ni atoms as buffering role during stretching process. These simulations yield valuable insights for exploring scalability and enhancing the development of irradiation hardening and embrittlement models.

Neutron and gamma radiation effects on thermal storage properties of polyethylene wax

Several nuclear reactors use ice condensers to condense steam in the case of a loss of coolant accident. These ice condensers have many problems that could be alleviated by using another material. The effects of low-dose neutron and gamma radiation on the thermal properties of polyethylene wax (PEW) were investigated for this purpose. PEW was irradiated in the Missouri University of Science and Technology Research Reactor (MSTR), the University of Missouri Cyclotron (MUC) and the University of Missouri Research Reactor (MURR) up to doses equivalent to 10 months in a nuclear power reactor's containment structure. The melting temperature and latent heat of fusion were determined using differential scanning calorimetry (DSC). Changes in the molecular bonds was determined using Raman spectroscopy. It was found that there was not a significant change in the thermal properties nor bonding over the investigated doses. This suggests that organic PCMs could be reliable alternatives to ice in nuclear reactor containment applications. The measured melting peak was found to be significantly wider expected by the suppliers' description. The ramifications of wide melting peaks are discussed in the context of reactor accident analysis and further experiments are suggested.

Low-dose neutron irradiation effects on the elastoplastic deformation mechanisms of aluminum-doped gallium nitride under contact loading

The elastoplastic deformation mechanisms of irradiated aluminum (Al)-doped gallium nitride (GaN) under contact loading are investigated in this work using the nanoindentation simulations, which is of great significance for understanding the mechanical properties of the Al-doped GaN and guiding the design of durable and high-performance GaN-based devices. The mechanical behaviors of the Al-doped GaN with different doping concentrations are analyzed, including the indentation hardness, Young's modulus, elastic recovery rates, phase transformations, and stress distribution. It is found that Al doping increases their hardness, Young's modulus, and elastic recovery rates, and leads to an enlargement of the phase transformation regions, which is dominated by the high coordination number (CN) phase transformations. Furthermore, the effects of low-dose neutron irradiation on their elastoplastic deformation mechanisms are studied by triggering cascade collisions within the structure. When subjected to such irradiation, structural changes occur in the Al-doped GaN, their indentation hardness, Young's modulus, and elastic recovery rates increase remarkably, and its phase transformation mechanism is changed remarkably. The dislocation behaviors of the doped and undoped GaN are different under neutron irradiation. This study is important for capturing the mechanical stability and integrity of Al-doped GaN in an irradiation environment, as well as developing GaN-based devices with superior irradiation resistance.

Comprehensive characterization of the irradiation effects of glassy carbon

Carbon materials have become increasingly diverse, finding applications in high-temperature and high-radiation environments. Glassy carbon, an allotrope known for its exceptional chemical inertness and desirable mechanical properties. However, understanding neutron irradiation effects in glassy carbon has proven challenging, primarily because of its unique nanopore structure. This study presents a highly detailed microstructural characterization investigation of neutron-induced changes in glassy carbon, revealing how changes in nanopore structure and crystallinity impact the irradiation-induced shrinkage. Aberration-corrected scanning transmission electron microscopy (STEM) reveals pore closure that leads to material densification in the irradiated samples. Dimensional analysis combined with comparison to historical data suggest significant length shrinkage to occur. Neutron and in situ electron irradiation experiments suggest that glassy carbon transforms into so-called carbon onions, supporting the concept of shrinkage saturation. Investigating irradiation temperature effects using STEM, electron energy loss spectroscopy, x-ray diffraction, and Raman spectroscopy revealed partial amorphization at 210 °C–230 °C and preserved order in glassy carbon at 860 °C, coinciding with pore closure. Thermal property measurements were also conducted to assess the effects of densification and other changes in the atomic structure of glassy carbon. The results of this study have broad implications in the deployment of glassy carbon to nuclear environments, based around the observed changes in the thermal properties, and demonstrates the operational window for the onset of densification.

Effect of gamma and neutron irradiations on the physical, magnetic and electrical properties of Ni–Cu–Cd nano-ferrites

The physical, magnetic and electrical properties variations for the sol-gel auto combustion synthesized Ni0.3Cu0.2Cd0.5Fe2O4 by gamma (γ) and neutron irradiations dose applications are studied in this research. The irradiation have been done through 2.0 × 1011 and 1.9 × 1012 cm−2s−1 per min fast neutron flux and γ rays from the research reactor of TRIGA MARK-II and 64 KCi cylindrical 60Co source respectively within room temperature. The rate of 1 Mrad and 3 Mrad dose is 1.067 Mrad/h. XRD results show greater intensities for the irradiation doses. Due to the redistribution of ions, changes in the lattice constant have been found by the irradiation through the results of XRD and Rietveld Refinement process. The saturated magnetization obtained from the VSM is found to decrease first by the irradiation and then increase drastically. This analysis is performed by the popular pulse field technique of hysteresis loop for nano ferrites and further analyzed by LAS. The frequency dependent characteristics such as dielectric constant, electric modulus, impedance analysis and ac conductivity are inspected for all samples with both types of irradiation process. The electrical modulus Cole-Cole plots insure the dominant property as electric stiffness for investigated ferrties. Extreme decrease has been found in the dielectric natures which also show good agreement in the higher ac conductivity nature at the higher frequencies. Electrical parametric dependent overlapping two semicircles which are not complete have been found in the plots of Cole-Cole for impedance data. The energy of activation for the process of diffusion decreases by the irradiation.

First-principles study on the microstructure, band structure, mechanical and optical properties of AB-stacked bilayer graphene under constant neutron irradiation with different electric field magnitudes and directions

Carbon-based devices have superior performance and lower power consumption compared to silicon-based devices. However, graphene and related two-dimensional materials are easily influenced by radiation due to their extremely high surface-to-volume ratio. Under constant neutron irradiation conditions, there have been no studies on the effects of the magnitude and direction of an external electric field on various properties of the AB system. This study systematically investigated the neutron irradiation effects on the AB system and the influence of the different electric fields on the properties of the AB system under constant irradiation conditions using the density functional theory and ab initio molecular dynamics method that assigns energy to the primary knock-on atom. The results indicate that under constant neutron irradiation with different electric fields, the changes in system configuration dominate the influence on band structure, while the impact of surface ripples is relatively limited. Reducing the interlayer spacing of the system can make the configuration more stable, which makes the band structure under the electric field more stable. The primary factors influencing the Young's modulus (Y) of the system are changes in the microstructure and the appearance of surface ripples, while the influence of system configuration is relatively limited. Under the irradiation conditions, the electric field can to some extent accurately modulate the band gap of the system. However, it will also correspondingly reduce the system's Y to a certain extent, causing negative impacts on the electrical and thermal conductivity.

First-principles study on the differences in mechanical and optoelectronic properties between monolayer graphene and AA bilayer graphene after neutron irradiation

Two-dimensional materials are easily affected by radiation. So far, there is no work to predict the neutron irradiation effects of AA bilayer graphene. Furthermore, the differences and comparisons of various properties between monolayer graphene and AA bilayer graphene after irradiation in the approximately same neutron environment have not been reported. In this study, the neutron irradiation processes on monolayer graphene and AA bilayer graphene were simulated in ab initio molecular dynamics. The mechanical, and optoelectronic properties of monolayer and AA bilayer systems before and after irradiation were calculated using the method based on density functional theory. The results indicate that the AA bilayer system is more resistant to neutron irradiation than the monolayer system. The bandgap of the monolayer (bilayer) system after irradiation will reach the order of 0.1 eV. This article has important value in exploring the methods of radiation reinforcement technology for carbon-based devices.

Design of a Facility for Simultaneous Irradiation with Two Ion Beams based on the HIPR Accelerator for Simulations Neutron Influence

Ion accelerator facility is a powerful tool to simulate neutron irradiation effects in reactor materials. Defects in the crystal lattice arise and the accumulation of transmutation products (helium and hydrogen) occurs in the structure of the material under the action of neutrons in the structural materials of nuclear installations. At Kurchatov Complex for Theoretical and Experimental Physics the heavy ion accelerator HIPr (heavy ion prototype) is used to simulate radiation damage in steels and alloys using a 5.6 MeV Fe2+ ion beam. The second beam line is designed at the HIPr facility to simultaneously implant helium (or hydrogen) into the region of defects. The second beam line provides a beam of helium ions with energy up to 300 keV. The report presents a description of second beam line design and a status of construction the second beam line.

Response of 11B enriched ZrB2 ultra-high temperature ceramic to neutron irradiation at elevated temperatures

ZrB2, an ultra-high temperature ceramic (UHTC) is being considered for use in fusion reactor first-wall structures, yet its response to irradiation remains poorly understood. This study employed scanning/transmission electron microscopy (S/TEM), synchrotron X-ray diffraction (XRD), finite element calculations, and thermal property measurements to thoroughly investigate the neutron-irradiation effects on 11B-enriched ZrB2. Neutron irradiations were conducted at 220 °C and 620 °C, with a neutron fluence of 2.2 × 1025 neutron/m2 (energy > 0.1 MeV), resulting in 3.9 dpa and 4200 appm He. The study revealed the unusual prevalence of prism loops and a > c anisotropic lattice swelling, likely linked to the low c/a ratio of ZrB2, leading to grain boundary microcracking. Reducing the grain sizes was effective in reducing intergranular cracking and macroscopic swelling. The observation of cavities in ZrB2 irradiated at 620 °C, as opposed to 220 °C, prompts questions about the temperature at which vacancies in ZrB2 become mobile, and the role of neutron absorption by 10B in elevating irradiation temperatures. Isotopic enrichment in 11B proves to be a viable strategy for mitigating helium production in transition-metal diborides, which is a critical consideration for nuclear applications. Irradiation-induced defects reduce the thermal diffusivity and conductivity of ZrB2 by a factor of 4–9, which has important implications for its role as a plasma-facing material in fusion reactors that drive high heat fluxes through first-wall materials. This comprehensive study lays the foundation for understanding ZrB2 behavior under neutron irradiation and highlights important phenomena to consider for various material applications.

Neutron irradiation and polarization effect of 4H–SiC Schottky detector

Neutron irradiation experiments were carried out on a 4H–SiC Schottky detector. The effects of neutron and accompanying γ-rays irradiation on the electrical properties, charge collection efficiency (CCE), energy resolution and crystal defects of 4H–SiC detectors were investigated. The total irradiation fluence was 1.24 × 1014 n/cm2, with an equivalent 1 MeV neutron fluence of 1.33 × 1015 n/cm2. Following neutron irradiation, the turn-on voltage increased significantly, and the capacitance of the Schottky junction no longer varied with the reverse bias voltage. The CCE of the detector decreased from 100% to 90.8%, while the energy resolution increased from 0.79% to 1.49%. The irradiated detector required a higher bias voltage for optimal performance. Additionally, we observed two defect levels, Ec-0.5 eV and Ec-0.35 eV, in the 4H–SiC crystals after irradiation. Their generation is also related to gamma ray irradiation. The detector exhibited a polarization effect, where the energy spectrum split into two distinct components during prolonged measurement of monoenergetic α particles. The peak position gradually shifted towards the lower energy side with increasing testing time. These effects can be mitigated by increasing the bias voltage to enhance the electric field strength in the drift region.

Effects of neutron irradiation on failure behavior analysis of high-density bumps under thermo-coupling conditions

As the space environment has conditions such as high vacuum, strong irradiation, and large temperature difference, spacecraft will face a series of challenges such as high-energy particles and extreme temperatures during on-orbit operation, especially neutron irradiation, which has a larger mean free range and a deeper depth of penetration, and which will cause serious damage to the electronic devices. Solder joints, the most failure-prone part of electronic devices, have received extensive attention from related researchers. In this study, the evolution of the microstructure of bumps under neutron irradiation and thermal field coupling conditions is analyzed utilizing scanning electron microscopy (SEM)\\electron backscatter diffraction (EBSD), and the changes in the mechanical properties of the bumps are also analyzed by nanoindentation tests and push-ball experiments. The results show that the incidence of high-energy neutrons generates a large number of atomic vacancies, which exacerbates the Kirkendall effect. The point defects caused by neutrons gather together to form defect clusters. These microscopic defects impede the movement of slip dislocations, leading to the hardening of the material and an increase in elastic modulus. In contrast, the accumulation of a large number of defects leads to the failure of the bump.

Effects of Gamma-ray and neutron irradiation on infrared optical properties of ZnSe and ZnS for ITER divertor thermography

Gamma-ray and neutron irradiation tests were performed by using antireflective-coated and non-antireflective-coated samples of ZnSe and ZnS to examine the impact on their infrared optical properties. In neutron irradiation tests, ZnSe and ZnS samples showed minimal transmittance reduction even up to 1.44 × 1016 n/cm2 (evaluated by dpa value, the values are 5.77 × 10−6, 2.07 × 10−5 for ZnSe and ZnS, respectively), about 5.8 times higher than the expected neutron fluence in ITER. Gamma irradiation at 100 kGy did not affect any of the samples, however, at 5.6 MGy (2.6x the expected dose of ITER), non-antireflective-coated ZnSe and ZnS exhibited induced absorption bands. Antireflective coating did partially mitigate this effect, but ZnS, even with antireflective coating, showed up to 2.5 % degradation over the wide wavelength range of 1.5–4.5 µm, whereas ZnSe was less affected. Both ZnSe and ZnS exhibited a modest 2 % absorption around 3 µm. Surface analysis by SEM, laser microscope, and XPS linked the 3-µm degradation to gamma-irradiation-induced Zn(OH)2 formation that was confined to the surface. Thus, transmittance degradation of ZnSe over the lifespan of ITER was estimated to be a maximum of approximately 7.8 %. The practical use of ZnSe in the IRTh system requires further evaluation with Si and CaF2 lenses and for the optical design to be finalized. Nevertheless, these findings suggest that ZnSe is a promising candidate for the IRTh system's lenses.

First-principles study on the effects of fast neutron irradiation and fast neutron irradiation under the external electric field on carbon-based material AB bilayer graphene

The irradiation damage mechanism of fast neutron irradiation and the fast neutron irradiation under the practical application of an additional electric field on carbon-based material AB bilayer graphene is not yet clear. This paper systematically investigates the impact of fast neutron irradiation and fast neutron irradiation under the practical application of the additional electric field (−0.2 V/Å) on carbon-based material AB bilayer graphene through density functional theory and molecular dynamics simulations. The research results indicate that the changes in the configuration of AB bilayer graphene and the appearance of surface ripples induced by fast neutron irradiation are the two main reasons for the alterations in the system's microstructure, band structure, Young's modulus, and optical properties, which may lead to performance degradation and damage of carbon-based devices. The further variation in the average interlayer spacing of the system under external electric field irradiation leads to the diversity of the system configuration, which ultimately leads to the diversity of the band structure of the system. The uncertainty in the type and width of the bandgap in AB bilayer graphene under fast neutron irradiation with an external electric field may be one of the reasons for the performance degradation and permanent damage of carbon based devices in practical applications. In the fast neutron irradiation environment, the precise control of the bandgap of AB bilayer graphene by an applied electric field will fail.

Neutron irradiation effect on superconductivity of Nb3Sn wire - 50 Hz data acquisition system -

A research facility for neutron irradiation effect on superconducting materials has been installed at Oarai center in Tohoku University in 2012 as part of a post irradiation experiment. It consists of a 15.5 T superconducting magnet, a variable temperature insert and a data acquisition and control system. Since the sample holder is cooled by thermal conduction with G-M refrigeration, there is a small temperature difference between positive and negative electrodes and the sample temperature rises during the critical current test due to joule heating. To evaluate the temperature rise precisely, a new data acquisition system with a sampling rate of 50 Hz has been installed. By measuring the temperatures of both electrodes and the voltage at the center of the sample, the temperature of the sample was estimated and the measured critical current (IC) was converted to the current at 4.2 K with a critical surface equation. The comparison of IC at different conditions including neutron irradiated samples was implemented and the neutron irradiation effect on superconductivity of Nb3Sn wire is discussed based on the 4.2 K superconductivity. This paper will describe the outline of the new data acquisition system and some results of neutron irradiated Nb3Sn wires.