Positron annihilation lifetime measurements of irradiated metals and alloys

The study uses the positron annihilation life time measurement method to investigate irradiation-induced defects in iron and iron alloys. Data on these defects are of great importance in analyzing the effects of heavy ion irradiation at high temperatures, such as on void swelling. Positron annihilation lifetime measurements are made on iron and an iron-10 % chromium alloy irradiated with neutrons or high-energy heavy ions. Irradiated metals are annealed to examine the behaviors and properties of the induced defects and defect clusters. Analysis of positron annihilation lifetime spectra shows that micro-void components exist in pure iron irradiated at room temperature. This agrees well with the fact that atomic vacancies move below room temperature. The components of interstitial atom clusters are found to recover stepwise. Micro-voids tend to recover at temperatures in the range of 300 deg C - 350 deg C. In an alloy containing 10 % chromium, vacancies move and disappear arround 200 deg C, while the corresponding temperature is 150 deg C for a carbon-containing two-phase alloy (Fe - 10 % Cr - 0.07 % C) and the Japanese ferritic/martensitic stainless steel (JEMS, a candidate fusion reactor wall material). The interstitial atom clusters in these alloys show very complicated behaviors, with recovery temperature ranging from about 300 deg C to 500 deg C, because different irradiation conditions lead to different forms of clusters. (Nogami, K.)