Computer Simulation of the Short-Term Annealing of Displacement Cascades

Abstract

An important source of damage to a solid exposed to high-energy neutrons (or ions) is the displacement of atoms from normal lattice sites. In a fast reactor, energies of tens of keV may be transferred to an atom and thus initiate a displacement cascade consisting of a localized high density of interstitials and vacancies. These defects will subsequently interact with one another to form clusters and to reduce their density by mutual annihilation. This short-term annealing has been simulated with a small computer using an atomic model of 7-iron based on the work of Johnson. The input cascades are due to Beeler. Results were obtained with both large (104 sites) and small (32 sites) annihilation regions. The former results in about one-half the residual defects of the latter, and a smaller fraction of clustered defects. Cluster size distributions and several examples of spatial distributions are given. Randomizing the spatial distribution of defects in a typical cascade geometry is found to diminish vacancy clustering and enhance interstitial clustering.