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

摘要

High Energy proton (up to 800 MeV) and spallation neutron irradiated samples of stainless steel 316L andMod 9CrlMo were studied using positron annihilation energy and lifetime spectroscopy. Irradiation damage caused to316L were up to 10 displacements per atom (dpa) and those for 9CrlMo were up to about 2.5dpa. Studies of T-parameter, which is calculated as the ratio of the number of counts in the wings of the Doppler-broadened 511 keVpeak to the number of counts in the center of the peak, showed that it dropped sharply from 0 to 3.5 dpa, and continueddropping up to 10 dpa in 316L. In 9CrlMo, similarly, T-parameter dropped sharply from 0 dpa to ldpa, but from 1 dpato 2.5 dpa it remained constant, indicating that the "effective" density of defects, as indicated by T-parameter saturatedwith the irradiation damage above 1 dpa in 9CrlMo. We saw no apparent change in the positron lifetime for radiationdamages above 3.5dpa in 316L. However, for steel 9CrlMo the positron lifetime in defects increased with irradiationdamage from 1.02 dpa to 2.46 dpa. This implies that the electron density at the annihilation sites, defects in this case,decreased. These results led us in both cases to investigate lower radiation damaged samples. We measured energy andlifetime spectra in 316L and 9CrlMo samples that were irradiated under the similar conditions as the above samples,but with radiation damage less than 0.1dpa. These results fill in some of the gap between 0 and 1 dpa and suggest thatmost of the change in T-parameter occurs at irradiation damages below 0.054 dpa.