Kinetics of helium self-trapping in metals

A kinetic model, based upon rate theory, is presented which provides a quantitative description of the processes leading to the self-trapping of helium introduced into metal lattices either by tritium decay or by sub-damage-threshold ion implantation. The model makes use of previously published binding energies of helium, vacancies, and self-interstitials to each other. A coupled set of diffusion and rate equations allowing for the diffusion of helium interstitials, vacancies, and tritium atoms and the trapping of helium, vacancies, and self-interstitials in clusters is solved with the use of methods applicable to those stiff equations. The results are compared with the tritium decay experiments of Thomas, Swansiger, and Baskes and the low-energy implantation experiments of Thomas and Bastasz. The model provides the necessary link between these experiments and the atomistic theory.