A numerical model of ion implantation into presolar grains

Pre-solar grains such as diamond and silicon carbide (found in primitive ch ondritic meteorites), contain isotopically anomalous noble gases. There are two ways that these could have become incorporated into the grains: direct assimilation during grain formation and growth, or subsequent addition aft er the grains had formed. Herein we investigate the latter possibility and explore the role of ion implantation within the interstellar medium (i.e. i nto pre-existing grains distributed in free space. Numerical models are der ived to address the issue of how ion implantation would affect the grain po pulation.