Effect Of Neutron Irradiation Research Articles

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.

Evaluation of the effects of neutron irradiation on first-generation corrosion mitigation coatings on SiC for accident-tolerant fuel cladding

High purity SiC and SiC/SiC composites coated with commercial TiN, Cr, CrN, or CrN/Cr multilayer coatings were irradiated in Ar or flowing PWR water in the Massachusetts Institute of Technology Nuclear Reactor Laboratory (MITR). Irradiation in Ar was performed in the core. In the water environment, identical samples were placed in one of three different locations: in-core, providing exposure to neutron damage and radiolysis-affected water; above-core, where samples were exposed to radiolysis-affected water but not neutron damage, or outside of the core, where samples were exposed to the coolant water without the effects of radiation. Radiation in Ar revealed significant cracking of all but the TiN coatings, attributed to differential swelling between the coating and substrate. Lattice swelling was not observed in any of the coatings, but 0.2% void swelling was observed in the Cr coating. All of the coatings failed during water exposures in the core. CrN/Cr spalled in each condition. Cr was protective, except under radiation damage as a result of cracking, and TiN severely degraded in the core with no coating was found following exposure. A SiC/coating ATF cladding system is expected to perform adequately following improvements in coating ductility and purity.

The combined effect of neutron irradiation and temozolomide on glioblastoma cell lines with different MGMT and P53 status

Temozolomide (TMZ) is a DNA-alkylating agent used for chemo-radiotherapy of glioblastoma, which is also a target cancer for boron neutron capture therapy (BNCT). Although the DNA-repair enzyme O6-methylguanine DNA methyltransferase (MGMT) and the tumor suppressor p53 are mutated in some glioblastoma cells, it remains unknown whether these mutations affect sensitivity to neutron irradiation. We examined sensitivity to neutron irradiation and TMZ in two glioblastoma cell lines: T98G, which is p53-mutant with high levels of MGMT activity; and A172, which is p53–wild-type and has low MGMT activity. T98G cells were more resistant to TMZ treatment than A172 cells, with a 10-fold higher LC50. In A172 cells, TMZ treatment did not change the cell-killing effect of neutron irradiation in the presence of borono-phenylalanine (BPA). By contrast, T98G cells were more resistant to neutron irradiation when BPA was present. These results indicate that DNA repair activity in T98G cells might be higher due to upregulation of MGMT after TMZ treatment. Thus, differences in the MGMT and p53 statuses of glioblastoma cells might predict the effect of combination therapy with BNCT and DNA-alkylating agent.

Thermal neutron irradiation effects on structural and electrical properties of n-type 4H\u2012SiC

In this article, the thermal neutron irradiation (NI) effects on the structural properties of n-4H–SiC and electrical properties of Al/n-4H–SiC Schottky contacts have been reported. The noticeable modifications observed in the irradiated samples were studied by using different techniques. The X-ray diffraction studies revealed a decrease in the lattice parameter of the irradiated samples due to isotopic modifications and irradiation-induced defects in the material. As a result, the energy bandgap, Urbach energy, longitudinal optical phonon‒plasmon coupling mode, free carrier concentration, defect related photoluminescence and nitrogen bound exciton photoluminescence bands were prominently affected in the irradiated samples. The current–voltage characteristics of neutron irradiated Al/n-4H–SiC Schottky contacts were also strikingly affected in terms of zero-bias offset as well as decrease in the forward current. These modifications along with the increase in the Schottky junction parameters (such as ideality factor, Schottky barrier height and series resistance) were attributed to neutron-induced isotopic effects and decrease in the free carrier concentration due to induced defect states.

Fracture failure analysis of steam generator channel heads with high carbon macro-segregation

Fast fracture evaluation strategy is receiving earnest concern in the structural integrity analysis of nuclear equipment which subjected to the effects of neutron irradiation during operation. The increment of ductile and brittle transition temperature is mainly due to the neutron irradiation which increases the risk of brittle fracture failure. In addition to the neutron irradiation, the high carbon macro-segregation of low-alloy steels also increases the risk of brittle fracture failure as the carbon positive macro-segregation will lead to the increasing ductile and brittle transition temperature of low-alloy steels. In the present study, a conservative relationship between the carbon content and the increment of ductile and brittle transition temperature is developed based on data and is used to the brittle fracture failure analysis of the highest carbon content region in SG channel head. A special defect size is assumed considering capability of non-destructive evaluation technology in the brittle fracture failure analysis. Results show that ratio between the calculated stress intensity factor according to safety coefficient suggested by ASME design code and the critical stress intensity factor is less than one, which indicates a safe design and no risk of brittle fracture failure for steam generator channel head considering high carbon macro-segregation.

Impact of Electrical Stress and Neutron Irradiation on Reliability of Silicon Carbide Power MOSFET

The combined effects of electrical stress and neutron irradiation of the last generation of commercial discrete silicon carbide power MOSFETs are studied. The single-event burnout (SEB) sensitivity during neutron irradiation is analyzed for unstressed and electrically stressed devices. For surviving devices, a comprehensive study of the breakdown voltage degradation is performed by coupling the electrical stress and irradiation effects. In addition, mutual influences between electrical stress and radiative constraints are investigated through TCAD modeling.

Swelling on neutron induced hexagonal boron nitride and hexagonal boron nitride-titanium diboride composites

In the present work, neutron irradiation effects on swelling were investigated for hexagonal boron nitride (hBN) and hexagonal boron nitride-titanium diboride (hBN-TiB2) composites. hBN and hBN-TiB2 composites were irradiated by reactor neutrons which include thermal, epithermal and fast neutrons at the central thimble of the reactor. The fast neutron (En > 0.1 MeV) and thermal neutron (En∼ 0.025 eV) fluxes were 1.44 × 1016 m−2 s−1 and 6.48 × 1016 m−2 s−1, respectively. The samples were induced by reactor neutrons up to total dose of 5.7 × 1020 m-2. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were carried out before and after irradiation of the samples. The lattice parameters and unit cell volumes were determined. The swelling percentages were calculated for hBN and hBN-TiB2 samples. For reactor neutrons irradiation, maximum swelling percentages were 4.29% for hBN and about 4.22% for hBN-TiB2 at the maximum exposed neutron dose. Furthermore, phase transition was observed from TiB2 to TiN phase in hBN-TiB2 composites with neutron irradiation. An experimental study was performed on hBN and hBN-TiB2 for nuclear applications (neutron detectors, control rods etc.).

ASSESMENT OF DAMAGE OF SOLAR HETEROJUNCTION a-SiC/c-Si INDUCED BY NEUTRON RADIATION

<span style="font-family: 'Times New Roman',serif; font-size: 10pt; -ms-layout-grid-mode: line; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-GB; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; mso-bidi-font-style: italic; mso-bidi-font-weight: bold;" lang="EN-GB">Amorphous silicon carbide is known as a material resistant except others influences also against radiation. This study investigates the effects of neutron radiation on electric characteristics (<em>I</em>-<em>V</em> characteristic, impedance spectra and obtained dynamic parameters of AC equivalent circuit) of solar cell a-SiC/c-Si heterojunction structure. The heterojunction structure was irradiated using neutrons with neutron fluence 10<sup>13</sup> cm<sup>-2</sup>. Existence of neutron induced structural defects, which could be introduced within semiconductor structure of heterojunction, has been illustrated using DC and AC analysis. </span><span style="font-family: 'Times New Roman',serif; font-size: 10pt; -ms-layout-grid-mode: line; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; mso-bidi-font-style: italic; mso-bidi-font-weight: bold;" lang="EN-US">The structural defects induced by neutron particles radiation affect mainly trapping mechanism. The process results in the changes of electronic elements included into proposed equivalent circuit.</span>

A portable fast neutron irradiation system for tumor therapy

A portable neutron tube was introduced as a small-sized (weight≤14.4 kg, power consumption ≤50W and cost≤ $100,000) neutron accelerator and applied for irradiation therapy on cancer. The effect of growth-inhibiting in vitro by neutrons irradiation on HeLa cells (human cervical cancer cells) was evaluated by colony formation assays, and cell apoptosis was evaluated by Flow Cytometry. A polyethylene protection device as the neutron moderator was designed and connected to the neutron tube to shield normal tissue and organs of the test animals from scatter radiation. Hematology and blood biochemistry were investigated to evaluate the protective effect of polyethylene. U14 (mice cervical cancer cell) tumor-bearing mice were further investigated to determine the tumor suppression effect of neutron irradiation. We found that cells showed a dose-dependent relationship after fast neutrons irradiation at different dose (1.11 Gy, 2.23 Gy, 3.34 Gy and 4.45Gy). Furthermore, in vivo experiments showed that the anti-tumor effect on U14 tumor-bearing mice greatly depended on the neutron irradiation dose. A high dose of fast neutron irradiation (26.73 Gy) could have tumor growth rate only 12.31% compared to 56.07% with control group. All the blood cell counts and blood biochemistry parameters were in the standard value ranges. Immunohistochemistry examinations clearly indicated the apoptosis cells in tumor tissues by the TUNEL assay. This work provides useful evidences on cancer irradiation therapy using fast neutron in pre-clinical study. And the neutron therapy system device has great potential to be a more convenient tool in clinical application with significantly lower power consumption, irradiation toxicity and cost.

Neutron irradiation effect on critical current of Nb3Sn wire under 8 T to 15.5 T

Superconducting magnets for fusion application will be irradiated by fast neutrons produced by fusion reaction, and it has been reported that the superconducting properties of the superconducting wires vary drastically by the irradiation. A bronze route Nb3Sn wire and an internal tin process wire were irradiated in a fission reactor up to 1.7 × 1023 n/m2 (> 0.1 MeV neutron), and the change in the critical current was measured by 15.5 T superconducting magnet and a variable temperature insert. The 4.9 × 1022 n/m2 irradiation for the bronze route wire increased the critical current by 1.75 times, but the 7.9 × 1022 n/m2 irradiation showed 1.03 times increase for the bronze route wire and 0.72 times decrease for the internal tin process wire. The 1.7 x 1023 n/m2 irradiation for the internal tin process wire decreased the critical current severely and the critical magnetic field down to around 16 T. This was the first result that the high fluence neutron irradiation caused the degradation of both the critical current and the critical magnetic field in this type of a Nb3Sn wire. Some irradiation defects will become the magnetic flux pining sites and strengthen the pining force. But the strong irradiation will damage the superconducting phase and degrade the properties.

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.

Assessment of mechanical properties of SPS-produced tungsten including effect of neutron irradiation

Production and supply of tungsten for the first wall fusion application is becoming an important aspect given the progress of ITER construction. Exploration of advanced routes alternative to the conventional powder metallurgy is currently undertaken. In this work we have assessed a potential of the spark plasma sintering (SPS) production route to deliver well controlled microstructure, chemistry and mechanical properties of bulk tungsten as a first step. SPS-produced tungsten was sintered at 2000 °C and was characterized in terms of mechanical properties, namely: tensile, three point bending and fracture toughness data in the temperaure range of 250–600 °C. Then, neutron irradiation was performed at 600 °C and the change of the fracture toughness was measured after irradiation together with the characterization of the fracture surface. The results are compared with those obtained for the commerically produced swaged tungsten irradiated and tested in equivalent conditions. The obtained results show that SPS technology offers the production of bulk tungsten with a good potential for further optimization (by e.g. swaging/rolling). Neutron irradiation causes the reduction of the fracture toughness comparable to the one induced in the commercially produced tungsten.

Effect of high-temperature neutron irradiation on fracture toughness of ITER-specification tungsten

The effect of neutron irradiation on the fracture toughness of two commercially pure tungsten materials processed according to ITER specifications has been investigated for three doses: 0.08 dpa, 0.44 dpa, and 0.67 dpa at 600 °C. The choice of this temperature was motivated by its technological importance due to the risk of irradiation-induced embrittlement. The temperature of 600 °C is below the void swelling peak temperature (∼800 °C) and, at the same time, well above the ductile to brittle transition temperature (DBTT) of the reference material (∼300 °C). Neutron irradiation was performed in the BR2 material test reactor inside the fuel channel in order to limit the transmutation of rhenium and osmium close to the rates expected in a fusion environment. The results of the mechanical tests performed up to 600 °C show that the fracture toughness decreases with the increase in the irradiation dose for both tungsten products. The fracture surfaces of the non- and irradiated specimens were systematically analysed to determine the evolution of the failure mechanisms.

Porous silicon (p-type) prepared by electrochemical etching and study of structure and morphology properties and effect of neutron irradiation

The research of electrochemical cell (ECE) for etching time ( 10 , 20 and 30 min. ) of the porous silicon (p-type) was fabricated by. This techniques and study at room temperature the irradiated by using neutron with flux density up 1012 cm-2 s -1 of high energy. The crystallographic structure and morphological properties of P-Si were investegated by X-ray diffraction (XRD) and Scanning electron microscope techniques before and after irradiation. The experimental results of X-ray reveal that P-Si layer still in crystallize phase and nano range. The morphological properties (Top surface and cross section) of P-Si layer were investigated by field emission Scanning electron microscope (FESEM) technique, these images illustrate that the pores diameter increase with height etching time. Finally , these results enhanced of the P-Si substrate after the irradiation. The effect of irradiation were best of structure of P-Si.

Влияние нейтронного облучения на твердость модифицированного ионами криптона никелида титана

Влияние нейтронного облучения на твердость модифицированного ионами криптона никелида титана

Effects of neutron irradiation on magnetic first-order reversal curves in reactor pressure vessel steels

We report results of measurements of first-order reversal curves (FORCs) for neutron irradiated reactor pressure vessel steels to seek their possible application to a nondestructive evaluation of the irradiation hardening. We find a peak position of the FORC distribution, which is the second derivative of measured FORCs, shifts towards zero field after neutron irradiation, associated with the narrowing of the peak width. The observations indicate the progress of the magnetic softening and magnetic homogeneity under neutron irradiation. The present investigations demonstrate that FORCs can offer additional information on microstructural changes due to neutron irradiation, which can not be obtained by a conventional hysteresis method.

Simulation of fracture of heat-resistant alloys under creep and neutron irradiation conditions

A numerical technique based on the finite element method of deformation processes and damage accumulation in structural elements made of heat-resistant alloys under high-temperature creep that accounts for the effect of neutron radiation is developed. The mechanical behavior of the material is described on the basis of previously developed general model of damaged material and creep model for unirradiated heat-resistant alloys, supplemented with taking into account the irradiation effect on creep rate and brittle fracture emerging in a given range of temperature and radiation intensity. The constitutive relations for creep model of irradiated material were obtained by modifying the creep model of the unirradiated material: a material function taking into account the effect of neutron flux on the strain rate of thermal creep is introduced; a material function taking into account the effect of neutron flux on creep surface radius is introduced; a material function taking into account the effect of neutron flux on the ultimate value of creep dissipation energy is introduced. To simulate the processes of brittle fracture during creep under neutron radiation, it is assumed that the destructive values of the effective normal stresses are the function of temperature, neutron flux and the current value of accumulated creep strain. To verify and illustrate the capabilities of the developed methodological and software tools, a number of problems on modeling the processes of high-temperature creep and fracture of structural elements made of heat-resistant alloy under consideration are solved.

922: Effects of near-continuous low-dose neutron irradiation on pregnancy outcomes in mice

Now that orbital spaceflight is a continuous reality, deep space exploration and extra-Earth colonization have become the aspirational activities of space agencies and private entities. Understanding the impact of the extraterrestrial environment on human reproduction is a vital precursor to extra-Earth colonization, however, the effects of microgravity and cosmic radiation on reproductive physiology remain largely unknown. Relevant forms of cosmic radiation include protons, heavy ions, and the secondary neutron irradiation that occurs as protons bombard spacecrafts, habitats, or the human body, and these forms of radiation are fundamentally different than gamma or x-irradiation. We hypothesize that exposure of pregnant mice throughout gestation to chronic low-dose neutron irradiation would result in increased miscarriage and restricted fetal growth. Following copulatory plug positivity, eighty 9-13-week old female C57BL/6 mice were randomized to near-continuous neutron irradiation (21 hours/day) using Califonium-252 at a dose rate of 1 mGy/day vs. control (background: 0.005 mGy/day) for the duration of pregnancy (E0.5-E18.5) at NASA’s Colorado State University Neutron Radiation Facility. The dams were then randomized to euthanasia at either E12.5 to determine the rate of early miscarriage, or E18.5 to assess the rate of late miscarriage, fetal anomalies, and growth restriction. Placentas were weighed and stored for future secondary analyses including placental immunohistochemistry, cell signaling and nutrient transport, and gene expression studies. Phenotypic characteristics are provided in Table 1. Chronic low-dose neutron irradiation caused increased early resorption rate and significantly decreased placental weight. In contrast, there were no differences in birth length, birth weight, or anomaly rate between groups. Although this data cannot be directly extrapolated to humans, for the first time, we show that near-continuous low-dose neutron irradiation pan-pregnancy at a space-relevant dose rate leads to increased risk of miscarriage in a mouse model.

Effects of plutonium dioxide encapsulation on the physico-chemical development of Portland cement blended grouts

The effects of alpha radiation on cementitious systems used for nuclear waste encapsulation, and the subsequent physico-chemical properties, have been subject to limited investigation comparative to the effects of gamma and neutron irradiations. This paper outlines an assessment of the impact of PuO2 incorporation on the bulk characteristics of BFS and PFA blended Portland cements, with specific focus on the microstructure, phase assemblage and the radiolysis of pore water. Cellulose was also added to the cements to investigate the effects of organics on these systems. Characterisation of the bulk phase assemblage and microstructure were completed using optical and scanning electron microscopy (SEM), x-ray diffraction (XRD), and thermogravimetric analysis (TGA). Gas evolution was measured to determine the radiolytic breakdown of pore solution. In all samples the PuO2 appeared well encapsulated, with good physical contact to the cement grout and no large scale defects observed. Pu-containing hydrates were not observed, but PuO2 containing BFS based systems showed variations in the ratio of sulfate-containing phases, with increased ettringite observed. Gas evolution results were consistent with expectations based on likely radiation deposition, and increased G(H2) values were observed for cellulose containing samples. The findings of this study suggest the investigated cements are suitable encapsulants matrices for wastes containing PuO2.

Influence of neutron irradiation on optoelectronic properties of structures with the InAs/GaAs quantum dots

The effect of neutron irradiation on the photosensitivity of the InAs/GaAs quantum dots has been investigated. It was shown that after neutron irradiation with a fluence of 1.5×1015 cm-2 the photosensitivity at the room temperature has been decreased at 3 times, whereas the shape of the photosensitivity’s temperature dependence didn’t reveal any visible changes, despite an appearance of defects in quantum dot layer. The effect was explained by the difficulty of a motion of photoexcited carriers in quantum dot layer to the recombination centres arised after irradiation.