PNNL

Abstract

Multiple interactions of displacement cascades with He-vacancy clusters are investigated using molecular dynamics simulations. The effects of a single displacement cascade on the stability of a He-vacancy (He-V) cluster depend on the He-to-vacancy (He/V) ratio and the primary knock-on atom (PKA) energy. Initial He-V clusters consist of 10 and 20 vacancies with He/V ratios ranging from 0.2 to 3 and the PKA energy, Ep, varying from 2 keV to 10 keV. The size of He-V clusters was found to generally increase with increasing He/V ratios for the same PKA energy, but the stability of He-V clusters decreases with increasing PKA energy. The results are compared with those for voids impacted by collisional cascades. During multiple 5 keV cascade events, the final size of He-V clusters depends on only the initial He/V ratios. It is of interest to notice that the number of vacancies in a He-V cluster is determined by the first cascade event, while subsequent cascade overlap has a significant effect on its stability. These results are discussed in terms of the internal pressure of He-V clusters, the mobility of He atoms, the number of vacancies produced by cascades and the He/V ratio.