Full molecular dynamics, and its binary collision approximation, were used in a complementary manner in order to study displacement cascade distributions. It was found that the Frenkel pair distributions were particularly narrow and symmetrical, and were well-described by their first moments. Quantitative molecular dynamics estimates were therefore possible. A comparison of the dependences of Frenkel-pair production upon primary energy, as predicted by both techniques, suggested a post-cascade recombination model. The variability in the spatial distributions of individual cascades was particularly large, due to instabilities which took place in the early stages of cascade development. The subsequent loss of correlation with the initial conditions was statistically demonstrated on the basis of binary collision approximation simulations of 5000 to 15000 cascades. Sufficient data could be obtained, using molecular dynamics, to characterise the spatial distributions within cascades. Systematic comparisons of molecular dynamics and binary collision approximations showed that, following the ballistic phase, the spatial extents of vacancies and interstitials tended to increase. This was related to atomic mixing in the cascade core. Such mixing was not predicted by the binary collision approximation. It was suggested to be responsible for the fragmentation of vacancy clusters which formed during the ballistic phase of cascades.

Atomic Displacement Cascade Distributions in Iron. A.Souidi, M.Hou, C.S.Becquart, C.Domain: Journal of Nuclear Materials, 2001, 295[2-3], 179–88