Damage structure due to displacement cascades in 14 MeV neutron-irradiated metals studied by positron lifetime and TEM techniques

Abstract

Transmission electron microscopy (TEM) and positron lifetime measurements were performed for Au, Cu, Ni, Fe, SUS316 and Fe-9Cr irradiated with 14 MeV D-T neutrons to (2.9–12.0) × 10 19 nm −2 at 333 and 423 K. TEM observations for the specimens irradiated at 333 K showed visible defect clusters in Au, Cu and Ni. There were no visible defect clusters in Fe, SUS316 and Fe-9Cr. Positron lifetime analysis and the trapping model analysis suggested an important role of invisible defect clusters during cascade defect formation. In Fe, the depleted zone from a single cascade event rarely collapses to a dislocation loop, and preferentially forms a three-dimensional vacancy cluster. Three-dimensional vacancy clusters are formed in Cu, Ni, Fe, SUS316 and Fe-9Cr. The size of these clusters is very small (di- or tri-vacancies) in SUS316 and Fe-9Cr because of the trapping of vacancies by impurities or solute atoms.