Statistical analysis of cluster production efficiency in MD simulations of cascades in copper

A large number of displacement cascades has been simulated using molecular dynamics (MD) for primary knock-on atoms (PKAs) of energy in the range 2-20 keV at 100 and 600 K. The defect production efficiency, intracascade clustering efficiency and fractions of self-interstitial atoms (SIAs) and vacancies contained in the clusters produced in the cascades were determined. The fractions of both SIAs and vacancies contained in clusters increased with increasing PKA energy and approached a saturation level at 20 keV. At both temperatures the clustered fraction of SIAs was higher than the clustered fraction of vacancies. This difference is larger at 600 K than that at 100 K and increases with increasing PKA energy. These results are compared with the corresponding values derived from experimental results. The comparison suggests that the single cascade simulations yield considerably higher values of the clustered fractions of both SIAs and vacancies primarily because the impact of intercascade defect reaction kinetics cannot be taken into account in the MD simulations.