Monte Carlo simulation of positron-stimulated secondary electron emission from solids

We have analyzed the problem of the secondary electrons emitted from a solid irradiated by a positron or electron particle beam. The relevant concepts that form the basis for a theoretical understanding of the secondary electron emission problem are reanalyzed by looking at Wolff's theory. However, to attain analytical results, such a theory must include some simplification, which may be valid in only a limited number of situations. To overcome such a limitation we have elaborated a Monte Carlo procedure for the calculation of the secondary electrons emitted from a solid, irradiated with a positron beam. The choice of a primary positron beam is justified because the experiments involving electron emission are not contaminated by the reemitted primary electrons. The calculations were performed in the positron primary energy range between 50 eV and 2 keV, and for different incidence angles with;respect to the surface of a copper sample. Many numerical results are reported, namely: i) the elastic mean-free paths of positrons in copper, ii) the mean number of electrons emitted per positron, iii) the penetration depth of the positrons, and iv) the depths from which the secondary electrons are emitted. Finally, the numerical results concerning the secondary electron energy distribution are compared with the experimental data recently presented by Overton and Coleman showing a general good agreement.