Positron annihilation study of the interaction between radiation defects and hydrogen in Ni and Fe

High-purity Fe and Ni were used. The interaction between radiation defects and hydrogen in them studied by a positron annihilation method at 100K and computer simulation. The positron lifetime in Fe irradiated by electron at low temperature was 175psec, which was thought the lifetime of positron captured in the single atom defect. The calculation result of the lifetime was 176psec, agreed with the experimental value. By electrical hydrogen charging, Fe did not change, but Ni and 316 stainless steel changed remarkably. About 150psec lifetime of positron was observed in Ni and it showed the defects within hydrogen and formation of micro void. 300psec long lifetime in 316 stainless steel was observed. Fundamental behaviors of point defects, clusters and interaction with dislocation in Fe and Ni were estimated by computer simulation. Peierls stress decreased with increasing loop size. This result is very important, because the single crowdion had been in the stable position, but when cluster formed, each crowdion took unstable position and bond energy generated, so that formation energy of cluster decreased. It leads to decrease Pierls potential and to the linear edge dislocation at the limit. (S.Y.)