20 keV monatomic and 40 keV diatomic As ions have been implanted into GaAs at room temperature and the resultant radiation damage measured by means of the channeling and back scattering of 1 MeV He+ions. The energy density within each diatomic cascade is approximately twice the density within the monatomic cascade. The radiation damage resulting from the diatomic implant is observed to be significantly larger (two to three times) than from the monatomic implants. This observation shows, quite directly, that when significant annealing of damage is occurring during implantation one cannot adequately describe the damage production in terms of quantities averaged over the implanted layer; account must be taken of the character (e.g. energy density) of the individual damage cascades.