STOCHASTIC ANNEALING SIMULATION OF DIFFERENTIAL DEFECT PRODUCTION IN HIGH-ENERGY CASCADES

Recent molecular dynamics (MD) studies have confirmed that significant clustering of both vacancies and self-interstitial atoms (SIAs) rakes place by the end of the quenching stage of a cascade, and that small interstitial clusters are glissile, with migration energies on the oi del of 0.1 eV. The spatial segregation and clustering of the vacancies and SIAs give rise to a differential production of mobile vacancies a nd SIAs that has a strong temperature dependence. At temperatures abov e recovery Stage V, vacancies can evaporate from clusters, while large SIA clusters produced in the cascade remain stable, leading to a diff erential increase of mobile vacancies that represents a 'production bi as' thai may be responsible for void swelling. The stochastic annealin g simulation code ALSOME is used to investigate quantitatively the dif ferential production of mobile vacancy and SIA defects as a function o f temperature for isolated 25 keV cascades in copper generated by MD s imulations. The ALSOME code and cascade annealing simulations are desc ribed, The annealing simulations indicate that above Stage V, where th e cascade vacancy clusters are unstable, nearly 80% of the post-quench vacancies escape the cascade volume, while about half of the post-que nch SIAs remain in clusters. The results are sensitive to the relative fractions of SIAs that reside in small, highly mobile clusters and in large, sessile clusters, respectively, which may depend on the cascad e energy.