Shizuka Shimanuki

Damage structure obtained by cross-sectional observation in silicon carbide irradiated with helium ions

Abstract The microstructural change due to He-ion irradiation has been studied by cross-sectional transmission electron microscope observation in hot-pressed SiC irradiated to 1 × 10 20 ions / m 2 at 300 and 1023 K. Dot and loop-shaped defect clusters are formed between 0.74 and 1.20 μm in depth from the ion-bombarded surface, and the damage peak depth is 1.15μm in the 1023 K irradiation. He bubbles, which are formed between 0.94 and 1.16 μm in depth, are aligned on the c -planes and along radiation-induced dislocations. In the 300 K irradiation, the amorphous zone is formed slightly behind the damage peak depth.

Electrical conductivity changes in silicon carbide under γ-ray irradiation

The effect of γ-ray irradiation on the electrical conductivity change has been studied by the in-situ measurement system at temperatures from 723 to 873 K in hot pressed SiC (HP-SiC) containing 2 wt.% BeO and pressureless sintered SiC (pls-SiC) containing 1 wt.% B and C. Increase of the conductivity is observed due to γ-ray irradiation in SiC, and the conductivity has a tendency to saturate up to a dose of about 2.5×10 4 Gy at each irradiation temperature. The conductivity shows similar values in pre-irradiated HP-SiC and pls-SiC at each temperature. However, the saturated conductivity in γ-ray irradiated HP-SiC is smaller than one in irradiated pls-SiC at the same irradiation temperature. It is considered that BeO existing along grain boundaries is effective to reduce the radiation-induced conductivity (RIC). RIC in HP- and pls-SiC recovers to almost the value in the preirradiation condition by annealing at the irradiation temperature. It is considered that the carriers excited by γ-ray irradiation are captured at the sites with deep energy level.

Intergranular stress corrosion cracking susceptibility of sensitized type 304 steel in 561 K pure water under γ-ray irradiation

Intergranular stress corrosion cracking (IGSCC) of sensitized type 304 stainless steel has been investigated in 561 K water under γ-ray irradiation at a flux of 2.6 × 103C kg−1h−1 by slow-strain-rate tensile tests. The IGSCC susceptibility was enhanced by γ-ray irradiation in water containing 8 ppm dissolved oxygen (DO). The DO dependence of the IGSCC susceptibility was observed in the water under γ-irradiation. Although slight IGSCC susceptibility was observed even in deaerated water (less than 1 ppb DO) under γ-ray irradiation, the susceptibility was completely suppressed by injection of hydrogen into the water. The enhancement of IGSCC susceptibility seems to be related to the formation of H2O2 in high temperature water by radiolysis under γ-ray irradiation and the H2O2 formation rate is markedly decreased by hydrogen injection.