THE CORRELATION OF DEFECT DISTRIBUTION IN COLLISIONAL PHASE WITH MEASURED CASCADE COLLAPSE PROBABILITY

The spatial distributions of atomic displacement at the end of the col lisional phase of cascade damage processes were calculated using the c omputer simulation code MARLOWE, which is based on the binary collisio n approximation (BCA). The densities of the atomic displacement were e valuated in high dense regions (HDRs) of cascades in several pure meta ls (Fe, Ni, Cu, Ag, Au, Mo and W). They were compared with the measure d cascade collapse probabilities reported in the literature where TEM observations were carried out using thin metal foils irradiated by low -dose ions at room temperature. We found that there exists the minimum or ''critical'' values of the atomic displacement densities for the H DR to collapse into TEM-visible vacancy clusters. The critical densiti es are generally independent of the cascade energy in the same metal. Furthermore, the material dependence of the critical densities can be explained by the difference in the vacancy mobility at the melting tem perature of target materials. This critical density calibration, which is extracted from the ion-irradiation experiments and the BCA simulat ions, is applied to estimation of cascade collapse probabilities in th e metals irradiated by fusion neutrons.