The importance of homogeneous and heterogeneous nucleation in the amorphization of silicon by ion implantation is considered. Previously a homogeneous model involving dose rate had been used to identify neutral vacancy and divacancy annealing as important mechanisms in the amorphization process. In an attempt to verify this dose rate model, experiments which detect the electron spin resonance signal from the amorphous regions have been performed. Both a light ion (N+) and a heavy ion (Kr+) at low (20 keV) and high (180 keV) energy were implanted into silicon at low (80°K) and higher (∼350°K) temperatures. No dose rate dependence was found, and the temperature dependence is not as predicted by the model. In addition, the production rate is not proportional to the dose to the one-half power-a power dependence which has previously been attributed to homogeneous nucleation. Furthermore, since the data agrees with the predictions of a heterogeneous model, it is concluded that homogeneous nucleation is not an important process in the amorphization of silicon by ion implantation.