Helium/hydrogen synergistic effect in reduced activation ferritic/martensitic steel investigated by slow positron beam

Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He2+ irradiation, (ii) H+ irradiation and (iii) He2+ irradiation followed by H+ irradiation, at temperature 450 oC. The presents of vacancy defects, represented by ?SHe+H parameter, induced by sequential irradiations was larger than the sum of defects, ?SHe parameter + ?SH parameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy.