PRIMARY KNOCK-ON ATOM ENERGY-DEPENDENCE OF CASCADE DAMAGE FORMATION AND INTERACTION

Defect production and microstructural evolution in fusion materials sh ould be evaluated based on the primary knock-on atom (PKA) energy spec trum. In this study, formation and interaction of cascade damage are e valuated as a function of PKA energy from irradiation experiments on t hin foils of gold irradiated with fission neutrons and 21 MeV self-ion s. These results are compared with fusion neutron irradiation data. Th e interaction of cascades at higher dose is found to result in the app earance of new clusters near the existing groups of vacancy clusters. These are considered to come from the conversion of invisible vacancy rich regions to visible clusters by near-by cascades. The minimum PKA energy to produce new visible clusters by interaction is estimated to be 165 keV, assuming that cascade zone size increases with damage ener gy.