Effect Of Neutron Irradiation Research Articles

Influence of neutron irradiation on the electronic properties of hexagonal boron nitride measured by terahertz time-domain spectroscopy

Due to the low atomic number of B, hexagonal boron nitride (hBN) has a large neutron scattering cross section and, therefore, is an ideal material for the realization of solid-state neutron detector. Here we apply the THz time-domain spectroscopy to study the effect of neutron irradiation on electronic properties of pyrolytic (PBN) and hot-pressed boron nitride (HBN). The key electronic parameters of these samples, such as the static dielectric constant ε b , the effective carrier density N*, the carrier relaxation time τ, and the electronic localization factor α, are determined optically, and their dependences upon the neutron irradiation fluence (NIF) are examined. We find that for hBN,N* and ε b decrease while τ and |α| increase with increasing NIF. These results can be used to further understand the neutron irradiation effects on the basic physical properties of hBN material. We believe that the results obtained from this work can benefit to the design and application of hBN material for neutron detectors.

LUE-40 LINAC BASED NEUTRON SOURCE FOR IRRADIATION TESTS OF HEP DETECTOR MATERIALS AND COMPONENTS

A photoneutrons source based on the NSC KIPT LUE-40 electron linac was designed and constructed to study the effect of neutron and gamma radiation on the properties of materials used in high-energy physics (HEP) detectors. The source was used to irradiate the optical elements of the PLUME detector in LHCb experiment with the neutron fluency of 1014 cm-2. Ways to increase the neutron yield, in particular, by installing an additional high Z metal shell are shown. At electron energy of 85 MeV, the neutron yield exceeds 10-2 neutron over one electron.

Effects of neutron radiation on the key component cells of upright metamorphic four-junction (UMM4J) solar cells

In this study, the bandgap of the top three junctions of the UMM4J solar cell was optimized based on the spectral matching principle. Three materials, namely AlGaInP (1.957 eV), AlInGaAs (1.495 eV), and InGaAs (1.171 eV), were selected as the materials for the top three sub-cells. The component cells were fabricated using metal organic chemical vapor deposition (MOCVD) to verify their radiation resistance performance. Neutron irradiation with an equivalent energy of 1 MeV and a fluence of 6 × 1013 cm−2 was used to evaluate the end-of-life performance. The light current-voltage (LIV) and external quantum efficiency (EQE) results reveal that the AlGaInP (1.957 eV) component cells demonstrate superior radiation resistance performance, while the InGaAs (1.171 eV) component cells exhibit the poorest radiation resistance performance. After ensuring a sufficient margin of degradation for the InGaAs (1.171 eV) sub-cells, the AlInGaAs (1.495 eV) component cells serve as the current-limiting junction before and after radiation, resulting in an enhanced radiation hardness of the UMM4J solar cell. Furthermore, deep level transient spectroscopy (DLTS) was employed to directly assess the radiation-induced defects of the three-component cells. The degradation of solar cell performance primarily stems from the defects that induce Shockley-Read-Hall (SRH) recombination.

Investigations of microstructure and tensile properties of neutron irradiated 6061 aluminum alloys

Effects of neutron irradiation on the microstructure and mechanical properties of CMRR (China Mianyang Research Reactor) structural material pure aluminum and 6061 alloy were studied by scanning/transmission electron microscopy (S/TEM) and tensile tests. The fast neutron (E > 0.1 MeV) fluences of 1.09–2.89 × 1022 n•cm−2 produced damage doses of 1.6–4.2 displacements per atom (dpa). Voids and faulted 1/3<111> dislocation loops were observed in both pure aluminum and 6061 alloy. In particular, voids tended to preferentially aggregate on coarse Cu-rich and fine Mg2Si precipitates which contributes to the higher irradiation tolerance in terms of void formation for 6061 alloy, suggesting that the uniformly distributed precipitates can act as trapping sites for defect clusters during irradiation and thus promote recombination. The size and density of Mg2Si precipitates showed a slight increase and Cu-rich precipitates emerged in 6061 alloy after neutron irradiation. Moreover, radiation-induced segregation was also detected along the grain boundaries. After tensile testing, the pure aluminum showed a lower yield strength and larger uniform elongation than 6061 alloy, where a moderate uniform elongation was still reserved after irradiation to 4.2dpa. The severely reduced ductility in 6061 alloy is supposed to be caused by the transmutation product silicon which contributes to the increase of dispersed multiple precipitates after irradiation. Our results indicate that precipitates especially Mg2Si play a decisive role in void suppression, but are not suitable in diminishing the radiation hardening.

Experimental investigation of neutron irradiation effects on α- alumina nanoparticles in water-based nanofluid for a light water reactor coolant

Nanoparticles offer several advantages in terms of heat transfer, stability, safety, and efficiency, making them an attractive option for reactor coolants. The feasibility of using α-alumina (α-Al2O3) nanoparticles as a component of coolant for a light water reactor was investigated under the high neutron flux conditions of a TRIGA Mark II research reactor. To achieve this, highly thermally conductive α-Al2O3 nanoparticles were synthesized using the sol-gel method. X-ray diffraction spectra analysis confirmed the crystal structure and the alpha (α) phase of the sample. The average crystal size was determined to be 55.5 nm. Transmission electron microscope analysis revealed that the nanoparticles had sizes ranging from 40 to 60 nm, although the shape of the particles was irregular. Thermogravimetric analysis indicated a weight loss of less than 0.5% over a temperature range from 30 °C to 1200 °C. Dynamic light scattering showed two intensity peaks at 129.6 nm and 623.2 nm, resulting in a Zeta average (Z) value of 474.9 nm and a polydispersity index of 0.688. In the TRIGA Mark II research reactor, the synthesized nanoparticles were exposed to a thermal neutron flux of 5.28 × 1012 n/cm2/s using a pneumatic transfer irradiation channel (rabbit system). This irradiation resulted in the formation of various activated products, including 28Al, 24Na, and 27Mg, with abundances of 50.5 ± 0.3%, 0.18 ± 0.02%, and 1.59 ± 0.06%, respectively. All of these nuclides are radioactive, with half-lives ranging from minutes to hours. The induced radioactivity in the reactor core area poses a risk of secondary radiation. The physicochemical interaction of these induced products, especially sodium (24Na), with the coolant and other components, is not safe, as sodium is a highly reactive element that can undergo an exothermic reaction with water. These findings suggest that the use of α-Al2O3 in water as a reactor coolant should be further examined from the viewpoints of neutron irradiation effects and the physicochemical interaction of activated products with core materials.

Combined anticancer effects of neutron radiation and genistein on prostate cancer cells

Prostate cancer is the most frequent cancer in men and the second largest cause of cancer-related mortality after lung cancer. Today, studies on neutron radiation therapy show that this method alone is not able to prevent the progression of the disease in most patients with prostate cancer, so it is better to combine neutron radiation with an auxiliary antitumor such as genistein. We found that genistein has anticancer properties and few antioxidant capabilities and could cause the death of prostate cancer cells, mostly through triggering apoptosis. Here the purpose of this study was to evaluate the effect of very low dose rate neutron irradiation emitted from 241Am-Be neutron source as well as the effect of the combination of neutron irradiation and adding the optimal concentration of genistein (480 μM) on the attenuation of prostate cancer PC3 cells in 3D culture environment. MTT assay, Neutral red assay, NO assay, Catalase activity, Reduced glutathione (GSH), Cytochrome c releasing, and Comet assay were used to assess the effect and type of mortality caused by neutron radiation and also neutron and genistein combination in prostate cancer cells. The results of cytotoxicity test reveal that very low dose rate neutron radiation (0.6 mGy/h) with or without genistein at 5, 10, 15, and 20h reduced the survival of prostate cancer cells. Moreover, the rate of necrosis due to the neutron effect at different irradiation times enhanced with the increasing time. Despite significant anticancer effect of Genistein, it cannot be used simultaneously with neutron radiation for prostate cancer treatment.

Neutron radiation induced effects in 4H-SiC PiN diodes

Silicon carbide (SiC) is a wide band gap semiconductor and an attractive candidate for applications in harsh environments such as space, fusion, or future high luminosity colliders. Due to the large band gap, the leakage currents in SiC devices are extremely small, even after irradiation to very high fluences, enabling operation without cooling and at high temperatures. This study investigates the effect of neutron irradiation on 50 μm p-n 4H-SiC diodes using current-voltage, capacitance-voltage, and charge collection efficiency (CCE) measurements up to neutron fluences of 1 × 1016 n eq/cm2. The leakage currents of the investigated devices remained extremely small, below 10 pA at 1.1 kV reverse bias. In the forward bias, a remarkable drop of the current was observed, which was attributed to an increased epi resistivity due to compensation of the epi layer doping by deep-level defects. The CCE was evaluated for alpha particles from a radioactive source, a 62.4 MeV proton beam at the MedAustron ion therapy center and using UV-TCT. The charge collection efficiency in reverse bias was shown to scale directly with the 1 MeV equivalent fluence Φeq as CCE∝Φeq -0.63±0.01. A CCE better than 50% was able to be obtained for fluences up to 1 × 1015 n eq/cm2. Because of the low currents in the forward direction, particle detection was also possible in forward bias, where the CCE was found to be increased relative to reverse bias. Furthermore, a significant dependency on the amount of injected charge was observed, with the CCE surpassing 100% in alpha and UV-TCT measurements, requiring further systematic investigation.

Effect of Neutron Irradiation on the Electronic and Optical Properties of AlGaAs/InGaAs-Based Quantum Well Structures.

The effect of neutron irradiation on the structural, optical, and electronic properties of doped strained heterostructures with AlGaAs/InGaAs/GaAs and AlGaAs/InGaAs/AlGaAs quantum wells was experimentally studied. Heterostructures with a two-dimensional electron gas of different layer constructions were subjected to neutron irradiation in the reactor channel with the fluence range of 2 × 1014 cm-2 ÷ 1.2 × 1016 cm-2. The low-temperature photoluminescence spectra, electron concentration and mobility, and high-resolution X-ray diffraction curves were measured after the deactivation. The paper discusses the effect of neutron dose on the conductivity and optical spectra of structures based on InGaAs quantum wells depending on the doping level. The limiting dose of neutron irradiation was also estimated for the successful utilization of AlGaAs/InGaAs/GaAs and AlGaAs/InGaAs/AlGaAs heterostructures in electronic applications.

Dose and dose rate dependence of precipitation in a series of surveillance RPV steels under ion and neutron irradiation

Life extension of light water reactors requires robust models to predict the embrittlement of reactor pressure vessel (RPV) steels under long-term neutron irradiation. Embrittlement is due to nanoscale precipitation hardening by phases containing Cu, Mn, Ni, and Si, resulting in increases of the ductile to brittle transition temperature. Embrittlement data for low flux, high fluence extended life conditions, up to 80 years or more, are largely not available. Thus, higher flux, accelerated test reactor irradiations have been used to help develop models to predict low flux embrittlement at high fluence. Here flux, or dose rate, is expressed in units of displacements per atom per second (dpa/s). The dose rate can significantly influence precipitate evolution in a way that depends on fluence (dpa), temperature, and alloy composition, as well as flux itself. Here, we explore precipitation in surveillance steels with varying compositions at high fluxes (10−5–10−6 dpa/s) produced using 70 MeV Fe2+ ion irradiations. Atom probe tomography was used to characterize the dose dependence of precipitation at very high ion irradiation dose rates, and to evaluate corresponding similarities or differences compared to neutron irradiated steels at a much lower dose rate of ≈ 5 × 10−9 dpa/s. The data show that, on average, the ion irradiation precipitate volume fractions increase by factors of ∼ 1.5 to 2 between 0.3 dpa and 1.2 dpa. Limited data show that the major effect of neutron versus ion irradiation is the former has lower precipitate number densities and larger sizes. Otherwise, the precipitates are remarkably similar in composition and volume fraction.

Effect of Neutron Irradiation on the Spectral Characteristics of InxGa1 – xN LEDs

Effect of Neutron Irradiation on the Spectral Characteristics of InxGa1 – xN LEDs

Effects of Fast Neutron Irradiation on Switching of Silicon Bipolar Junction Transistor

Background: When bipolar junction transistors (BJTs) are used as switches, their switching characteristics can be deteriorated because the recombination time of the minority carriers is long during turn-off transient. When BJTs operate as low frequency switches, the power dissipation in the on-state is large. However, when BJTs operate as high frequency switches, the power dissipation during switching transients increases rapidly.Materials and Methods: When silicon (Si) BJTs are irradiated by fast neutrons, defects occur in the Si bulk, shortening the lifetime of the minority carriers. Fast neutron irradiation mainly creates displacement damage in the Si bulk rather than a total ionization dose effect. Defects caused by fast neutron irradiation shorten the lifetime of minority carriers of BJTs. Furthermore, these defects change the switching characteristics of BJTs.Results and Discussion: In this study, experimental results on the switching characteristics of a pnp Si BJT before and after fast neutron irradiation are presented. The results show that the switching characteristics are improved by fast neutron irradiation, but power dissipation in the on-state is large when the fast neutrons are irradiated excessively.Conclusion: The switching characteristics of a pnp Si BJT were improved by fast neutron irradiation.

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.

Effect of neutron irradiation to 0.7 dpa and 1.4 dpa on the tensile properties and fracture surface of EUROFER97 steel

Several grades of reduced-activation ferritic-martensitic (RAFM) steels have been proposed for fusion applications (e.g., blanket first wall) since the 1990s all over the world. Four batches of the European reference RAFM steel EUROFER97 have been produced since 1998. The RCC-MRx design code, developed for applications including fusion reactors, currently contains a provisional section dedicated to EUROFER97, encompassing properties of the first two batches, whereas a minimum of three batches are required for a full qualification and final inclusion of a material into RCC-MRx. The EUROfusion project coordinates efforts to broaden the knowledge of EUROFER97 properties relevant for fusion reactors ITER and DEMO, preparing them for closing the database gaps in RCC-MRx, and adding them in the DEMO material property handbook (MPH). Its purpose is to provide average and minimum curves of required properties according to the DEMO engineering design and manufacturing needs.The present work reports for the first time tensile properties and fractographic analysis of neutron-irradiated EUROFER97 Batch 4. The measured strength and ductility are in line with the data already contained in the MPH. SEM investigation confirms that dimple fracture is retained in the material in the temperature range 25–550 °C after neutron irradiation up to 1.4 dpa.

Assessment of neutron irradiation effects via PKA spectra, displacement damage, and gas production: Application to reactor pressure vessel

Neutron irradiation damage is a major challenge for materials employed in radiation environments, such as Reactor Pressure Vessels (RPV). Based on a determined neutron flux, the present study assesses the neutron irradiation effects via Primary Knock-on Atoms (PKAs) production, the consequent displacement damage, and gas production. The complete PKA spectra including all minor isotopes from nuclear reactions are calculated and used to estimate the displacement damage and gas production. At the inner surface of the RPV, which suffers the strongest neutron irradiation, it is found that some minor PKAs have smaller atomic numbers and higher kinetic energies than dominant isotopes in RPV. These PKAs have much deeper ranges in RPV steel and may thus produce important damage other than point defects. The displacement damage is calculated using SRIM simulations and the corresponding corrections to ensure consistency with the NRT-dpa concept. Notably, the displacement damage in the RPV should be ∼23% higher than the prediction by the NRT-dpa formula, which cannot be directly applied to PKAs different from the target atom. The 4.1 H-appm/dpa and 0.2 He-appm/dpa gas productions at the RPV inner surface are higher than that in the innermost 1/4 thickness by a factor of 2 and 1.3, respectively.

Microstructural characterisation of brittle fracture initiation sites in reactor pressure vessel steels

Neutron embrittlement of reactor pressure vessel (RPV) steels potentially limits the safe operational time of nuclear reactors. In tested RPV steel samples microcracks are known to originate from cleaved precipitates, inclusions or grain boundaries, which eventually lead to brittle fracture. In most cases, these precipitates are reported as carbides. Latest research indicates the critical fracture event to be the crossing of grain boundary instead of the particle–matrix interface by the microcrack. Very few works have performed detailed fractography, which revealed the size and type of the feature found in the crack nucleation centre, together with metallographic bulk investigations. Additionally, the effect of subsequent neutron irradiation on microcrack nucleation is unknown. In the present work, detailed fractography and metallography is performed on a RPV steel in both its unirradiated as well as neutron irradiated state. A particle in the centre of the initiation site has been identified in a majority of the cases, while no specific type of particles were involved in more than 1/3 of all samples. Those particles are either Mo-rich carbides or Al-rich inclusions. In comparison, the metallographic analysis of the bulk steel reveals Mo-rich and Mn-rich carbides. Mn-rich carbides constitute the majority of all carbides in the steel but are never found to be responsible for brittle fracture initiation. Only a small fraction of observable carbides is Mo-rich which are responsible for fracture. Thus, the present work demonstrates a discrepancy between particles found in brittle fracture initiation sites and particles that are directly observable in bulk steel. Some of the initiating particles are extremely rare in the bulk. Furthermore, it is revealed that the local fracture stress does not depend on the type or size of particle or grain involved at the initiation site. In conclusion, the fracture stress strongly depends on the type of the grain boundary, rather than on a stress based upon a Griffith criterion, which considers particle or grain size alone. The brittle fracture mechanism was found to be unaffected by neutron irradiation. These findings could help refine modelling of the critical brittle fracture stress and fracture toughness using microstructural parameters as input.

Infrared spectroscopy of nanocrystalline anatase (TiO2) particles under the neutron irradiation

Bands structure of nanocrystalline anatase (TiO2) particles was investigated before and after neutron irradiation (1.6 × 1015n·cm−2, 8 × 1015n·cm−2, 4 × 1016n·cm−2 and 2 × 1017n·cm−2) using FTIR spectroscopy. The peaks expressing Ti – O and Ti – O – Ti stretching oscillations before and after neutron irradiation were explained with appropriate wavenumber in the infrared (IR) absorption spectra. The new peaks observed in the IR spectra as a result of neutron transmutations were analyzed with V – O or V – O – H deformation oscillations of the newly formed V isotope. Simultaneously, deformation vibration of the TiO6 octahedron were detected on the nanoparticle surface. Moreover, the effect of neutron irradiation on the surface activity of anatase nanoparticles and amorphization processes in nanocrystals were explained by their corresponding IR spectra.

In situ observation of crystal reorientation in polygranular graphite by synchrotron X-ray diffraction and neutron imaging

The capacity of polygranular graphite to accommodate strain is important to its use within structural components. This study has used in situ neutron and synchrotron X-ray experiments to demonstrate that reorientation of crystal domains accompanies the accommodation of applied mechanical strain in unirradiated Gilsocarbon (GCMB/IM24) graphite. Orientation changes were observed using 3D X-ray Diffraction, and local changes in neutron scattering were also observed with energy-resolved Bragg-edge neutron imaging. In both cases, this behaviour at the crystal level was partially recovered when the load was removed. This study provides new evidence for crystal deformation mechanisms that contribute to polycrystalline graphite's elastic non-linearity and the development of permanent set, which may also explain the effects of fast neutron irradiation on graphite elastic behaviour.

Comparing neutron and helium ion irradiation damage of REBa2Cu3O coated conductor using x-ray absorption spectroscopy

Understanding the effects of high energy neutron damage on REBa2Cu3O (REBCO) coated conductor is of vital importance for the design of the magnetic confinement systems for compact nuclear fusion power plants. However, neutron irradiation campaigns can only be carried out in a few facilities, and the experiments are very slow and expensive partly because the samples become radioactive. Ion irradiation provides an easily accessible alternative route to studying the effects of radiation on high temperature superconductors, which not only increases the volume of technical data that can be obtained but also enables more complex experiments such as in situ cryogenic irradiation. The question is, does ion damage offer a good proxy for neutrons? Here we use high energy resolution fluorescence detected x-ray absorption spectroscopy to probe the effects of fast neutron irradiation on the local environment around the copper ions in the REBCO layer of coated conductor tapes. We find that the spectral changes are similar to those induced by helium ion irradiation, suggesting that both projectiles produce the same types of structural defect in the REBCO lattice, although there is some evidence of an additional type of defect present in the sample heavily damaged by He+ ion irradiation. It is also shown that the linear degradation of superconducting transition temperature (T c ) of coated conductors with the calculated number of displacements per atom occurs at the same rate for neutrons and helium ions. Together these results provide new evidence suggesting that helium ions can emulate neutron point defect damage in REBCO high temperature superconductor reasonably well, increasing confidence that helium ions could be used as a useful proxy for neutrons in future experiments.

Tensile properties of modified 316 stainless steel (PNC316) after neutron irradiation over 100 dpa

ABSTRACT The effects of fast neutron irradiation on tensile properties of 20% cold-worked modified 316 austenitic stainless steel (PNC316), which was improved swelling resistance and creep strength, claddings and wrappers for fast reactors were investigated. PNC316 claddings and wrappers were irradiated in the experimental fast reactor Joyo at irradiation temperatures between 400°C and 735°C to fast neutron doses ranging from 21 to 125 dpa. The post-irradiation tensile tests were carried out at room and irradiation temperatures. Elongations of PNC316 measured by the tensile tests were maintained at an engineering level, although the material incurred significant irradiation hardening and softening depending on irradiation temperature. The maximum swelling of PNC316 wrappers was about 2.5 vol.% at irradiation temperature between 400°C and 500°C up to 110 dpa. Japanese 20% cold-worked austenitic steels, PNC316 and 15Cr-20Ni, had sufficient ductility and work-hardenability even after above 10 vol.% swelling, while they had very weak plastic instabilities.

Influence of neutron irradiation on X-ray diffraction, Raman spectrum and photoluminescence from pyrolytic and hot-pressed hexagonal boron nitride

Hexagonal boron nitride (hBN) is considered as an ideal semiconductor material for solid-state neutron detector, owing to its large neutron scattering section because of the low atomic number of B and excellent physical properties. Here we study the influence of neutron irradiation on crystal structure and on intermediate energy state (IMES) levels induced by the presence of impurities and defects in hBN. Large-size and thick pyrolytic and hot-pressed hBN (PBN and HBN) samples, which can be directly applied for neutron detector devices, are prepared and bombarded by neutrons with different irradiation fluences. The SEM and TEM are used to observe the sample difference of PBN and HBN. X-ray diffraction and Raman spectroscopy are applied to examine the influence of neutron irradiation on lattice structures along different crystal directions of PBN and HBN samples. Photoluminescence (PL) is employed to study the effect of neutron irradiation on IMESs in these samples. We find that the neutron irradiation does not alter the in-plane lattice structures of both PBN and HBN samples, but it can release the inter-layer tensions induced by sample growth of the PBN samples. Interestingly and surprisingly, the neutron irradiation does not affect the IMES levels responsible for PL generation, where PL is attributed mainly from phonon-assisted radiative electron-hole coupling for both PBN and HBN samples. Furthermore, the results indicate that the neutron irradiation can weaken the effective carrier-phonon coupling and exciton transitions in PBN and HBN samples. Overall, both PBN and HBN samples show some degree of the resistance to neutron irradiation in terms of these basic physical properties. The interesting and important findings from this work can help us to gain an in-depth understanding of the influence of neutron irradiation on basic physical properties of hBN materials. These effects can be taken into account when designing and applying the hBN materials for neutron detectors.