Positron annihilation lifetime studies of stainless steel under proton and Xe irradiation

Highlights: • Analyze the effect of small cluster with H atoms on positron annihilation short lifetime parameter. • Explain the short lifetime parameter variations by positron annihilation at precipitated phase. • Explain the increase of the long lifetime parameter with proton irradiation by gas atoms-vacancies development. - Abstract: Specimens of stainless steel reactor internals were irradiated with 240 keV protons and 6 MeV Xe ions up to 15 dpa. The positron annihilation lifetime spectroscopy (PLS) was carried out to study the development of vacancy-type defects. It is indicated that positrons are trapped by vacancies, vacancy clusters and other defects (precipitate, dislocations). The short lifetime parameter τ₁ decreases when specimens are irradiated to 2 dpa by proton, whereas in the case of Xe irradiation, τ₁ decreases when specimens are irradiated to 7 dpa. The positron annihilation at small cluster with H atoms (for H irradiation) and precipitated phase (for Xe irradiation) may explain this transition. The long lifetime parameter τ₂ increases continuously with damage increase. Compared with Xe irradiated specimens, a larger τ₂ is obtained in proton irradiated specimens at the same damage. The gas atoms-vacancies, which are expected to be the early state of H bubbles, will develop into small bubbles with the increase of irradiation damage and thus cause long lifetime parameter increase.