Positron Annihilation Energy and Lifetime Spectroscopy Studies for Radiation Defects in Stainless Steel

Abstract

High Energy proton (up to 800 MeV) and spallation neutron irradiated samples of stainless steel 316 L and Mod 9 CrlMo were studied using positron annihilation energy and lifetime spectroscopy. Irradiation damage caused to 316 L were up to 10 displacements per atom (dpa) and those for 9 CrlMo were up to about 2.5 dpa. Studies of T‐parameter, which is calculated as the ratio of the number of counts in the wings of the Doppler‐broadened 511 keV peak to the number of counts in the center of the peak, showed that it dropped sharply from 0 to 3.5 dpa, and continued dropping up to 10 dpa in 316 L. In 9 CrlMo, similarly, T‐parameter dropped sharply from 0 dpa to 1 dpa, but from 1 dpa to 2.5 dpa it remained constant, indicating that the “effective” density of defects, as indicated by T‐parameter saturated with the irradiation damage above 1 dpa in 9 CrlMo. We saw no apparent change in the positron lifetime for radiation damages above 3.5 dpa in 316 L. However, for steel 9 CrlMo the positron lifetime in defects inc...