Variability in atomic collision cascade distributions

The origin of the variance in several properties characterizing atomic collision cascades in crystals and polycrystals is investigated by full molecular dynamics and its binary collision approximation. The critical dependence of the cascade development on the initial conditions is evidenced. In the case of internal irradiation, as a consequence of this instability, atomic thermal displacements from equilibrium lattice sites are sufficient to induce a complete loss of correlation with the initial conditions before the end of the cascade development, Thermal disorder turns out to be the leading factor determining the spatial configuration distributions of induced stable point defects, which are particularly broad and skewed. In contrast with spatial distributions, the frequency distributions of Frenkel pairs are known to be particularly narrow. An explanation is suggested, based on the vacancy-interstitial distance distributions which are also found to be uncorrelated from the initial conditions.