Effect Of Fast Neutron Irradiation Research Articles

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.

A Review of the Effects of Fast-Neutron Irradiation on the Performance of 4H-SiC Schottky Barrier Detectors

A Review of the Effects of Fast-Neutron Irradiation on the Performance of 4H-SiC Schottky Barrier Detectors

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.

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.

Understanding the nanoscale chemistry of as-received and fast neutron irradiated Nb3Sn RRP® wires using atom probe tomography

Atom probe tomography (APT) has been used to study the effect of fast neutron irradiation on the local chemistry of Nb3Sn samples. Two RRP® wires doped with 2 at% Ti were analysed, one in the as-received condition and the other irradiated to a neutron fluence (E > 0.1 MeV) of 2.82 × 1022m−2 in the TRIGA-II reactor. The irradiated sample had a reduced T c, an increase in F p, a shift in the peak of the F p curve suggesting the introduction of secondary point pinning, and an increase in the estimated scaling field B*. APT analysis has shown that polycrystalline Nb3Sn has three distinct regions of composition, near stoichiometry Nb3Sn (low Nb), regions with a higher Nb content than expected in equilibrium Nb3Sn (high Nb) and grain boundaries. The summed composition of these three regions lies within the Nb3Sn phase for both the as-received and irradiated samples. The distinct regions of high Nb Nb3Sn demonstrate incomplete diffusion in the as-received sample, and the reduction in volume of these high Nb regions after irradiation implies significant radiation induced diffusion has occurred. The presence of other features in the atomic-scale chemistry, such as the extent of Cu segregation at grain boundaries, three types of dislocation array, and unreacted Nb nanoparticles, are compared between samples.

Effects of fast and thermal neutron irradiation on Ga-polar and N-polar GaN diodes

Studies of the radiation tolerance and electrical behavior of gallium nitride (GaN) based devices are important for the next generation of high-power and high-voltage electronics that may be subjected to harsh environments such as nuclear reactor and fusion facilities, particle accelerators, and post-denotation environments. In this work, we study the behavior of Ga-polar and N-polar GaN Schottky diodes before and after exposure to fast and thermal + fast neutrons. Temperature-dependent current–voltage (I–V) and circular transmission line method (CTLM) measurements were used to study the electrical characteristics. A strong reduction in reverse leakage current and an increase in differential resistance in forward bias were observed after neutron irradiation. Thermionic emission (TE), Frenkel–Poole (FP) emission, and Fowler–Nordheim (FN) tunneling models were used to explain the forward and reverse I–V characteristics pre- and post-irradiation. The study confirms that Ga-polar and N-polar GaN Schottky diodes exhibit different electrical responses to fast and thermal neutron irradiations. The reverse bias characteristics of N-polar diodes are less affected after the fast neutron irradiation compared to Ga-polar diodes, while in the forward bias region, the electrical behavior after fast and thermal neutron irradiations is similar in Ga-polar and N-polar diodes. The results indicate that the role of orientation should be considered in the design of GaN-based radiation-tolerant electronics.

Analysis of Dimensional Change in Zr-2.5%Nb CANDU Pressure Tube Material aged at 300-400°C using Neutron Diffraction

The primary boundary of the CANDU reactor consists of Zr-2.5%Nb alloy pressure tubes and SA106 alloy feeder pipes. The pressure tubes are exposed to fast neutron (E>1Mev) irradiation during reactor operation, and experience dimensional changes. The actual dimensional change in the pressure tube during in-service operation is greater than the design estimate. It is not fully understood what is responsible for the dimensional changes in the pressure tubes. In this study, to accelerate the aging effect on the pressure tube material, aging was performed at 300-400°C for up to 20,000 hours and neutron diffraction was used to track variation in lattice spacing, thereby identifying the reason for the dimensional change. The analysis result showed that α-Zr, the main phase of Zr-2.5%Nb, had little dimensional change at 350°C or lower. On the other hand, the aging treatment at 400°C resulted in anisotropic expansion in the α-Zr of the HCP crystal, of 0.02% and 0.08% in the (1010) and (0002) directions, respectively. It was confirmed that above 350oC the β-phase in the Zr-2.5%Nb alloy was decomposed to precipitate β-Nb . The driving force of the lattice expansion may be due to the diffusing out tendency of the super saturated Nb in α-Zr and due to the residual cold working effect applied during the manufacturing process. The enhancing effects of fast neutron irradiation on lattice diffusion are discussed in detail.

Fast neutron irradiation effects on Si- and GaN-based avalanche photodiodes

We report the behaviour of the dark current and gain characteristics of Si- and GaN-based avalanche photodiodes (APDs) irradiated by fast neutrons. For Si-based APDs, the dark current increases with the increase of neutron fluence, indicating that the avalanche property has been seriously affected. The gain values of Si-based APD slightly increase after irradiation by a low neutron fluence of 1.0 × 1012 cm−2, while the device exhibits gain degradation as the fluence increases to 1.0 × 1013 cm−2 or even above at high reverse bias voltage, unlike the previous studies where only degradation was observed. The steep increase of dark current and gain when approaching the breakdown voltage after neutron irradiation indicate that the avalanche property is almost unaffected for GaN-based APDs. Furthermore, we infer that the optical absorption between acceptor state and conduction band in the p-type layer plays an important role in influencing the change of dark current and gain at high reverse bias voltage. The findings not only enrich the understanding of neutron irradiation effect on Si- and GaN-based APDs, but also experimentally prove that GaN-based APDs hold better radiation resistance than Si-based devices.

Study of color centers in radiation-modified diamonds

We report on the optical properties of He-related color centers created by He-ion implantation and subsequent thermal annealing in natural diamonds, including the temperature (300–700 K) and excitation power (1–1800 kW/cm2)-dependent photoluminescence (PL) measurements. The prospects for the use of He-implanted diamonds for temperature sensing are discussed. The effect of fast neutron irradiation on the optical properties of Si-V color centers in CVD diamonds were also examined.

Methods of Redox Control and Measurement in Molten NaCl-CaCl2-UCl3

The U.S. Department of Energy is currently supporting the design and planned construction of the Versatile Test Reactor (VTR) capable of performing experiments in a fast neutron field. This will allow for study of the effect of fast neutron irradiation on nuclear fuels, materials, and functional components. The molten salt irradiation experiment will utilize the VTR to study the chemical changes and speciation in molten chloride and/or fluoride salts.In preparation for future experiments involving irradiation of candidate molten salt fuels, the redox potential measurement and control methods in molten NaCl-CaCl2-UCl3 at 500oC were studied. The goal was to identify a metal/metal chloride redox buffer that can be used to control the redox potential, thereby helping to mitigate the corrosion risks posed by irradiation of the uranium salt fuel. An ideal candidate would both adequately reduce the redox potential and possess a low neutron interaction cross section.The first metal/metal chloride redox buffer investigated was Zr/ZrCl4. ZrCl4 has a standard state reduction potential of -2.02 V vs. Cl-/Cl2 at 500° C. The standard state reduction potentials for UCl3 and CrCl2 are -2.41 and -1.55 V, respectively. Zr metal should, thus, oxidize to ZrCl4 and control the redox potential at a level that simultaneously prevents Cr corrosion while leaving UCl3 unreduced from the salt.In order to test Zr metal for redox control, a 6.2-mm diameter Zr rod (99%) was submerged in molten NaCl-CaCl2-UCl3 salt at 600°C. The open circuit potential (OCP) of the salt was measured at a tungsten working electrode vs a Ag/AgCl reference electrode encased in a mullite tube. NiCl2 was added to the salt to simulate the effect of fission on redox potential. After submerging the Zr rod, the measured open circuit potential between the W WE and the RE dropped by -0.63 V over a period of 100 minutes.There is concern as to whether the rate of reaction of insoluble Zr metal with the salt can keep up with the rate of potential change due to the irradiation of the salt. Other redox buffer candidates being considered include uranium, calcium, and sodium. The latter two choices are attractive because of their predicted solubility in the molten salt, supporting homogenous redox control reactions. The problem with the latter three choices is that amounts contacted with the salt will need to be precisely controlled to avoid reduction of UCl3. OCP measurements will also be reported for molten NaCl-CaCl2-UCl3 using U, Na, and Ca as the redox buffer. Conclusions will be drawn regarding the most effective metal to use in the future VTR experiments in order to control the redox potential of the irradiated salt.

Pulsed fast reactor neutron irradiation effects in Si doped n-type β-Ga2O3

The effects of pulsed neutron irradiation on Si doped n-type β-Ga2O3 films grown by halide vapor phase epitaxy (HVPE) on bulk Sn doped n+ β-Ga2O3 substrates are reported. This irradiation leads to an almost linear increase with neutron fluence of the density of deep electron traps E2* (Ec − 0.74 eV), E3 (Ec − 1.05 eV), and E4 (Ec − 1.2 eV), with an introduction rate close to 0.4–0.6 cm−1 while the density of the E2 traps (Ec − 0.8 eV) related to Fe was virtually unchanged. In addition, the increase in the density of deep traps with optical ionization threshold of 1.3 eV, 2.3 eV, and 3.1 eV with an introduction rate close to 0.8–2 cm−1 was observed. The carrier removal rate under our conditions was 28 cm−1. Neutron irradiation also led to a measurable decrease of the diffusion length of nonequilibrium charge carriers. The results are qualitatively similar to previous reports for proton and α-particle irradiation of HVPE β-Ga2O3. When comparing the findings with those described earlier for bulk neutron irradiated Ga2O3, we observe lower starting densities of electron and hole traps and lower introduction rates for these traps in the epitaxial structures. The carrier removal rates were comparable to those in bulk crystals.

Influence of Fast Neutron Irradiation on the Electrical and Optical Properties of Li Doped ZnSnO Thin Film Transistor

The effects of fast neutron irradiation on the electrical and optical properties of Li (3 at%) doped ZnSnO (ZTO) thin films fabricated using a sol-gel process are investigated. From the results of Li-ZTO TFT characteristics according to change of neutron irradiation time, the saturation mobility is found to increase and threshold voltage values shift to a negative direction from 1,000 s neutron irradiation time. X-ray photoelectron spectroscopy analysis of the O 1s core level shows that the relative area of oxygen vacancies is almost unchanged with different irradiation times. From the results of band alignment, it is confirmed that, due to the increase of electron carrier concentration, the Fermi level (EF) of the sample irradiated for 1,000 s is located at the position closest to the conduction band minimum. The increase in electron concentration is considered by looking at the shallow band edge state under the conduction band edge formed by fast neutron irradiation of more than 1,000 s.

Suppressed neurogenesis without cognitive deficits: effects of fast neutron irradiation in mice.

This study assessed the effects of combined low-dose neutron and γ-ray irradiation on hippocampal neurogenesis and hippocampal-dependent memory. Neural progenitor cell division and survival were evaluated in brain sections and whole hippocampal preparations following head irradiation at a dose of 0.34 Gy for neutron radiation and 0.36 Gy for γ-ray radiation. Hippocampal-dependent memory formation was tested in a contextual fear conditioning task following irradiation at doses of 0.4 Gy for neutron radiation and 0.42 Gy for γ-ray radiation. Cell division was suppressed consistently along the entire dorsoventral axis of the hippocampus 24 h after the irradiation, but quiescent stem cells remained unaffected. The control and irradiated mice showed no differences in terms of exploratory behavior or anxiety 6 weeks after the irradiation. The ability to form hippocampus-dependent memory was also unaffected. The data may be indicative of a negligible effect of the low-dose of fast neutron irradiation and the neurogenesis suppression on animal behavior at 6 weeks after irradiation.

Fast-neutron irradiation effects on monolayer MoS2

We investigated neutron irradiation effects on monolayer MoS2 by photoluminescence (PL), Raman and X-ray photoelectron spectroscopy. Results revealed that Mo and S defects and oxidation replacements of S vacancies were generated by neutron irradiation, leading to the red-shifts and broadenings of the and A1g Raman modes, as well as the red-shift of the A-exciton peak and quenching in the PL spectra. The relative atomic content ratio of S to Mo decreased with the increase of neutron flux, indicating that the neutron irradiation assisted in the release of S atoms.

The effect of fast neutron irradiation on the superconducting properties of REBCO coated conductors with and without artificial pinning centers

Superconductors are essential components of future fusion power plants. The magnet coils responsible for producing the field required for confining the fusion plasma are exposed to considerable neutron radiation. This makes irradiation studies necessary for understanding the radiation response of the superconductor. High temperature superconductors are promising candidates as magnet coil materials. YBCO and GdBCO tapes of several manufacturers were irradiated to fast neutron fluences of up to 3.9 × 1022 m−2 in the research reactor at the Atominstitut. Low energy neutrons contribute to the fission reactor spectrum but not to the expected spectrum at the fusion magnets. Low energy neutrons have to be shielded in irradiation experiments to avoid their substantial effect on the superconducting properties of tapes containing gadolinium. The critical current (Ic) of the tapes in this study was examined at fields of up to 15 T and down to a temperature of 30 K. Ic first increases upon irradiation and reaches a maximum at a certain fluence, which depends highly on temperature, being highest at low temperature. Ic declines at high fluences and eventually degrades with respect to its initial value. Tapes with artificial pinning centers (APCs) degrade at lower fluences than tapes without them. The n-values decrease in all types of tapes after irradiation even when the critical currents are increased. The field dependence of the volume pinning force differs in pristine tapes with and without APCs but shows the same behavior after irradiation.

Morphological and Phenotypic Effects of Fast Neutron Irradiation (FNI) on Lagos Spinach (<i>Celosia argentea</i> L.)

Fast neutrons irradiation is a valuable tool for developing varieties with high agricultural potentials and economic values. Therefore, the research was carried to evaluate effects of fast neutron irradiation on the morphology and phenotype of Lagos spinach, with the aim of inducing useful agronomical traits for selection of desirable genotypes that could be used for large scale production. The <i>Celosia argentia</i> (Red accession) that were used for the experiment were obtained from local far

Mutagenic Effects of Sodium Azide and Fast Neutron Irradiation on the Cytological Parameters of M2 Lagos Spinach (Celosia argentea var cristata L.)

The effects of fast neutron irradiation (FNI) and sodium azide (SA) on the pollen and cytological parameters of Celosia argentea was carried out. M1 seeds of treated C. argentea plant with fast neutron and sodium azide were collected from the seed bank of Department of Biological Sciences, Federal University of Technology, Minna, Nigeria and raised on the field to maturity stage. Young flower buds were collected from the plants for cytological studies. Cytological analysis of the plants revealed heterogeneous size of pollen grains, with three distinct variant of 29.12, 34.31 and 39.21 µm. The least average pollen diameters (32.66 µm) was recorded in 6.00 mM SA and the highest (37.58 µm) in 4.00 µS FNI. Significant variation (p≥0.05) in the numbers of pollen production per flower and anther were obtained. Lower percentage pollen fertilities were recorded in all the treated plants when compared with the control (94.15 %). However, these values were insignificance (p≤0.05), except for 8.00 mM which had the least of percentage pollen fertility of 71.62 %. The phenomenon of pollen restitution caused by abnormal meiotic division resulted in the formation of dyad, triad and tetrad in higher irradiated doses plants. Cytological analysis of the plant indicated that 8.00 µS had the highest mitotic index with metaphase (56.56) being the most frequent stage followed by telophase (28.40). Meiotic chromosomal counts revealed n = 18 at metaphase, with the formation of dyad and tetrad in most of the treated plants and the control. Abnormal meiotic division in 4.00 mM and 12.00 µS resulted in triad division. Observation from this study therefore, revealed that pollen restitution coupled with high mitotic index in 8 µS confer greater reproductive advantages to the plant.

Generation of peanut mutants by fast neutron irradiation combined with in vitro culture.

Induced mutations have played an important role in the development of new plant varieties. In this study, we investigated the effects of fast neutron irradiation on somatic embryogenesis combined with plant regeneration in embryonic leaflet culture to develop new peanut (Arachis hypogaea L.) germplasm for breeding. The dry seeds of the elite cultivar Luhua 11 were irradiated with fast neutrons at dosages of 9.7, 14.0 and 18.0 Gy. The embryonic leaflets were separated and incubated in a medium with 10.0-mg/l 2,4-D to induce somatic embryogenesis. Next, they were incubated in a medium with 4.0-mg/l BAP for plant regeneration. As the irradiation dosage increased, the frequency of both somatic embryo formation and plantlet regeneration decreased. The regenerated plantlets were grafted onto rootstocks and were transplanted into the field. Later, the mature seeds of the regenerated plants were harvested. The M2 generation plants from most of the regenerated cultivars exhibited variations and segregation in vigor, plant height, branch and pod number, pod size, and pod shape. To determine whether the phenotypes were associated with genomic modification, we compared the DNA polymorphisms between the wild-type plants and 19 M3-generation individuals from different regenerated plants. We used 20 pairs of simple sequence repeat (SSR) primers and detected polymorphisms between most of the mutants and the wild-type plants (Luhua 11). Our results indicate that using a combination of fast neutron irradiation and tissue culture is an effective approach for creating new peanut germplasm.