Distribution of the number of emitted electrons for MeV H+- and He2+-ion impact on metals

The statistical distribution of the number of emitted electrons induced by MeV H+ and He2+ impact on aluminum, copper, and gold targets was measured. The obtained results are very well represented by a Polya distribution. Based on a simplified theoretical picture the appearance of a Polya distribution in this context can be explained by cascade processes, which permits a quantitative estimation of the distributions in good agreement with the experiments for all investigated projectile-target combinations. The deviation from a Poisson distribution is given by the relative importance of cascade processes compared to projectile-induced processes