Magnetic hysteresis properties of neutron-irradiated VVER440-type nuclear reactor pressure vessel steels

The development of non-destructive evaluation methods for irradiation embrittlement in nuclear reactor pressure vessel steels has a key role for safe and long-term operation of nuclear power plants. In this study, we have investigated the effect of neutron irradiation on base and weld metals of Russian VVER440-type reactor pressure vessel steels by measurements of magnetic minor hysteresis loops. A minor-loop coefficient, which is obtained from a scaling power-law relation of minor-loop parameters and is a sensitive indicator of internal stress, is found to change with neutron fluence for both metals. While the coefficient for base metal exhibits a local maximum at low fluence and a subsequent slow decrease, that for weld metal monotonically decreases with fluence. The observed results are explained by competing mechanisms of nanoscale defect formation and recovery, among which the latter process plays a dominant role for magnetic property changes in weld metal due to its ferritic microstructure.     

In-situ TEM observation of the evolution of helium bubbles in Mo during He+ irradiation and post-irradiation annealing

The evolution of helium bubbles in purity Mo was investigated by in-situ transmission electron microscopy (TEM) during 30 keV He⁺ irradiation (at 673 K and 1173 K) and post-irradiation annealing (after 30 keV He⁺ irradiation with the fluence of 5.74×10¹⁶ He⁺/cm² at 673 K). Both He⁺ irradiation and subsequently annealing induced the initiation, aggregation, and growth of helium bubbles. Temperature had a significant effect on the initiation and evolution of helium bubbles. The higher the irradiation temperature was, the larger the bubble size at the same irradiation fluence would be. At 1173 K irradiation, helium bubbles nucleated and grew preferentially at grain boundaries and showed super large size, which would induce the formation of microcracks. At the same time, the geometry of helium bubbles changed from sphericity to polyhedron. The polyhedral bubbles preferred to grow in the shape bounded by {100} planes. After statistical analysis of the characteristic parameters of helium bubbles, the functions between the average size, number density of helium bubbles, swelling rate and irradiation damage were obtained. Meanwhile, an empirical formula for calculating the size of helium bubbles during the annealing was also provided.     

Effects of neutron irradiation and subsequent annealing on the optical characteristics of sapphire

In this paper, the effect of neutron irradiation on sapphire single crystal with fast neutron of 1.0×10¹⁸ and 1.0×10¹⁹ neutrons/cm² has been investigated along with the effect of annealing temperature. It is found that the colorless transparent sapphire single crystals were turned yellow after 10 MeV fast neutron irradiation at room temperature. There are peaks at 206, 230, 258, 305, 358 and 452 nm after neutron irradiation. And the intensity of optical absorption bands decrease with wavelength and annealing temperature. A new absorption peak at 452 nm was found after isothermal annealing at 400 °C for 10 min, which was ascribed to F₂⁺ color center. Because of the recombination of interstitial ions and vacancies, color centers were almost removed after annealing at 1000 °C. The TL peaks were found to shift to higher temperature after neutron irradiation. And a higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks at 176 and 227 °C.     

光电倍增管中子直照灵敏度响应

光电倍增管的中子直照响应对脉冲中子探测器的设计和实际应用具有重要影响。分析了中子束直接照射光电倍增管产生直照响应的过程和机理。中子与光电倍增管入射窗硼硅玻璃中的硼和硅发生(n,α)和(n,p)反应,导致窗玻璃产生荧光,从而使光阴极发射光电子。在5SDH-2小串列加速器上,选用9815B和9850B两种光电倍增管进行实验,得到了光电倍增管的中子直照灵敏度能谱响应曲线。结果表明：中子能量由低到高变化时,光电倍增管的中子直照灵敏度也随之增大;两种光电倍增管的中子直照灵敏度比值为1.9×102~2.74×102,该值与其相应的增益比量级一致。     

Change of GeSx parameters after neutron irradiation

In the paper some experimental results on the dependence of thermal conductivity, temperature conductivity coefficient, heat capacity, dc conductivity and ac conductivity on integrated neutron flux within the range from 10¹⁶ n cm^–2 to 10¹⁹ n cm^–2 are described. At integrated neutron flux of 10¹⁷ n cm^–2 an extreme in all parameters was observed. This effect can be explained by means of compensation of unsaturated bonds in the glass due to defects caused by irradiation.     

光电倍增管中子直照灵敏度响应

 光电倍增管的中子直照响应对脉冲中子探测器的设计和实际应用具有重要影响。分析了中子束直接照射光电倍增管产生直照响应的过程和机理。中子与光电倍增管入射窗硼硅玻璃中的硼和硅发生(n,α)和(n,p)反应,导致窗玻璃产生荧光,从而使光阴极发射光电子。在5SDH-2小串列加速器上,选用9815B和9850B两种光电倍增管进行实验,得到了光电倍增管的中子直照灵敏度能谱响应曲线。结果表明：中子能量由低到高变化时,光电倍增管的中子直照灵敏度也随之增大;两种光电倍增管的中子直照灵敏度比值为1.9×10²~2.74×10²,该值与其相应的增益比量级一致。     

Nanocrystalline alloys of Fe-Cu-Nb-Si-B after neutron irradiation

Transmission Mössbauer spectroscopy was used to study changes induced by irradiation of amorphous and nanocrystalline samples. In an as-cast sample neutrons mostly affect the orientation of a net magnetic moment. The average hyperfine field decreases towards higher neutron fluencies. In the case of the nanocrystalline samples a new disordered structure is created in the amorpous remainder corresponding to boride phases as it is shown in the samples isothermally heated from 1 to 8 hours. The structural changes of the amorphous remainder depend on the stage of crystallization and total neutron fluencies.     

Comparison between post-irradiation annealing and post-high electric field stress annealing of n-channel power VDMOSFETs

The behavior of the defects created in the gate oxide and at the Si/SiO₂ interface of n-channel power vertical double-diffused metal-oxide-semiconductor field-effect transistors (VDMOSFETs) by irradiation and positive high electric field stress have been investigated. Interface traps exhibit the same behavior after both types of stress, while there are significant differences in post-stress responses of the charge trapped in the oxide, consisting of fixed and switching component.     

Laser on porous silicon after oxidation by irradiation and annealing

Stimulated emission has been observed from oxide structure of silicon when optically excited by 514 nm laser. The photoluminescence (PL) pulse has a Lorentzian shape with a full width at half maximum (FWHM) of 0.5-0.6 nm. The twin peaks at 694 nm and 692 nm are dominated by stimulated emission which can be demonstrated by its threshold behavior and transition from sub-threshold to linear evolution in light emission. The gain coefficient from the evolution of the peak-emission intensity as a function of the optically pumped sample length has been measured. The oxide structure was fabricated by laser irradiation and annealing treatment on silicon. A model for explaining the stimulated emission has been proposed in which the trap states of the interface between oxide of silicon and porous nanocrystal play an important role.     

Short-range order of amorphous FeNiB alloy after neutron irradiation

Transmission Mössbauer spectroscopy was used to study irradiation-induced changes in the short-range order of an amorphous Fe_80-x Ni _x B₂₀ alloy. Neutron irradiation led to an increase of the width of a hyperfine field distribution implying atomic rearrangement towards disordering. Changes in a mean value of a HFD and Mössbauer line areas can be associated with a reorientation of spins due to radiation damage.     

Recovery of copper alloys after neutron irradiation at low temperatures

The effects of fast neutron irradiation near 4.2°K on dilute Cu, Cu₃Au, α-CuZn, β-CuZn and CuNi alloys were studied by electrical resistivity measurements. For Cu₃Au, the recovery stage at ～ 100°K becomes more distinct with increasing long-range order, and is attributed to migration of interstitials. The ratio of the number of replacements to the number of displacements (C _R /C _F ) is estimated to be about 50 for neutron irradiation, in contrast to the previously reported value of ～2 for electron irradiation. For α-CuZn, a large recovery stage at ～150°K is found and attributed to annihilation of interstitids whose migration produces ordering. For β-CuZn, migration of interstitials also produces ordering. It is also suggested that in β-CuZn, the ratio C _R /C _F is larger for neutron irradiation than for electron irradiation as in the case of Cu₃Au. The results on CuNi alloys are presented without explanation.     

Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1?×?10¹² to 2?×?10¹⁵ cm^?2, corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si–Si and C–C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8?dpa (i.e. ion fluence of 3?×?10¹⁴ cm^?2). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8?dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 °C up to 1500 °C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 °C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 °C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.     

Optical properties of polycrystalline alumina after irradiation with iron ions and annealing

Optical absorption of polycrystalline corundum (polycor) after irradiation with iron ions and subsequent annealing in vacuum was studied. It was found that substitutional, intrinsic radiation, biographical defects, and complexes on their basis have an effect on the absorption parameters and optical transitions between localized states and allowed bands. The contributions to changes in the optical properties of individual substitutional defects, their clusters, and complexes with the participation of substitutional defects and radiation defects were singled out. The influence of defects and iron oxides formed upon annealing on absorption was estimated. The most proable nature of clusters of substitutional defects and impurity-vacancy complexes was identified.     

Defects in CaF2 caused by long-time irradiation and their response to annealing

Samples of CaF₂ irradiated for millions of years in nature were studied by several methods, including X-Ray diffraction, positron annihilation spectroscopy (PAS), photoluminescence spectroscopy (PLS) and transmission electron microscopy (TEM). It was found that the unexpectedly high density of radiation-induced defects present in the fluorite structure (documented by TEM) causes significant micro-strains. Even annealing up to 450°C cannot completely remove these micro-strains, which are stabilised by impurities. PAS and subsequent theoretical calculations revealed the behaviour of the defects during heating. The PL spectra of irradiated fluorite were also interpreted.     

Recovery of electrical resistivity in amorphous pdsi alloys after low temperature neutron irradiation

Measurements of electrical resistivity after low temperature fast neutron irradiation are made for amorphous Pd₈₀Si₂₀ and Pd₈₀Ni₂Sl₁₈ and then Pd₈₀Si₂₀ annealed at 230°C and 360°C, and the isochronal annealing curves are obtained. The resistivity increase of Pd₈₀Si₂₀ annealed at 360°C is about 10 times larger than that of amorphous alloys and no defined annealing stage is observed in amorphous alloys and Pd₈₀Si₂₀ annealed at 360°C. For amorphous Pd₈₀Si₂₀, about 60% of the resistivity increase by irradiation remains after annealing up to room temperature and these are discussed by the structural relaxation.     

Analysis of multiple cell upset sensitivity in bulk CMOS SRAM after neutron irradiation

In our previous studies, we have proved that neutron irradiation can decrease the single event latch-up(SEL) sensitivity of CMOS SRAM. And one of the key contributions to the multiple cell upset(MCU) is the parasitic bipolar amplification,it bring us to study the impact of neutron irradiation on the SRAM's MCU sensitivity. After the neutron experiment, we test the devices' function and electrical parameters. Then, we use the heavy ion fluence to examine the changes on the devices' MCU sensitivity pre-and post-neutron-irradiation. Unfortunately, neutron irradiation makes the MCU phenomenon worse.Finally, we use the electric static discharge(ESD) testing technology to deduce the experimental results and find that the changes on the WPM region take the lead rather than the changes on the parasitic bipolar amplification for the 90 nm process.     

Kinetics of the radiation-induced hardening of EP-823 steel after Ni++ ion irradiation, annealing, and re-irradiation

The ferritic-martensitic steel 12Cr-MoWSiVNbB (EP-823) was irradiated with Ni⁺⁺ ions with the energy 7 MeV, and fluences of 2.7 × 10²⁰ and 3.9 × 10²⁰ ion/m² at 380 C. The irradiated samples were annealed at 600°C and then re-irradiated under the same conditions. After re-irradiation, the microhardness increased to the maximum value and achieved about 70% of the value corresponding to that after primary irradiation. After primary and secondary irradiation with increasing doses, the hardening reaches its saturation level at approximately similar damaging doses and behaves similar to that obtained in the case of the neutron irradiation of ferritic chromium steels.     

Measurement of internal friction and shear modulus of aluminium-magnesium alloy after neutron irradiation at 78 K

The internal friction and shear modulus of polycrystalline Al + 3 at.% Mg was studied as a function of temperature after fast neutron irradiation, at liquid nitrogen temperature (78 K). The initial increase of shear modulus after irradiation is mainly due to the dislocation pinning of the irradiation induced defects. The further increase of shear modulus during annealing is caused by the bulk-effect. The recovery of shear modulus up to room temperature is similar to that of the residual electrical resistivity after a low temperature neutron irradiation. However, we may point out that in contrast to stage II, in stage III we observe a recovery of shear modulus that is distinctly more pronounced than that of electrical resistivity. The temperature dependence of internal friction, before irradiation, shows a peak at 230 K. After neutron irradiation we observe no peak in the temperature region, from 90 K to 300 K.