Slow positron beam study of highly irradiated RPV steel under proton and ion impact

Abstract Ion irradiation combined with a slow positron beam could be used to evaluate irradiation damage correlated with embrittlement of nuclear materials. In this study, the evolutions of irradiation-induced defects in reactor pressure vessel steel exposed to 240-keV proton and 3-MeV Fe 13+ ion irradiations with the same dose of 0.05, 0.14, 0.35, 1.37, and 2.26 displacements per atom (dpa) at a low temperature are investigated. Vacancy-type defects were produced by both proton and Fe 13+ ion irradiation. The S parameters of proton-irradiated pure Fe and RPV steel increased with the dose and did not tend to a saturated value up to a high dose (2.26 dpa). The S parameters showed a saturated value at low doses after Fe 13+ ion irradiation. This is because heavy ions can more easily produce larger open-volume vacancy-type defects than light ions at low dose.