Fluctuations in collision cascades: Ion beam mixing

We have studied the consequences of statistical fluctuations in collision cascades on mixing of atoms in dense collision cascades. The distributions of energy densities in spherical and cylindrical spikes are obtained from Monte Carlo simulations of collision cascades where a simple model is used for grouping recoils into separate subcascades. The subcascades are approximated as either spherical or cylindrical. In the latter case we find a decrease by a factor of ten and two in the mixing rate when Au is mixed by 7 MeV Ag and 650 keV Kr ions, respectively, if the mean energy deposition is used instead of distribution. New experimental results from 7 MeV Ag ion bombardment of AuPt multilayers at 12 and 300 K are reported. The calculated values for mixing rates agree with the measured values.