Comparative study of secondary electron emission from solids under positron and electron impacts

Secondary electron emission from gold caused by the impacts of positrons an d electrons at keV or less energy is investigated by means of a Monte Carlo simulation of elastic and inelastic collision processes of the projectiles and cascade electrons inside the solid. The cross-section for the elastic collision of each particle with an atom in the solid is calculated using th e partial wave expansion technique, whereas the cross-section for the inela stic collision or for the electron excitation is calculated from the Ashley 's optical-data model. Because of less large-angle elastic scattering of th e positron, the calculated backscattering coefficient is smaller for the po sitron than the electron. At low impact energies (<600 eV), however, the ca lculated secondary electron yield for the positron is larger than that for the electron, due to the larger inelastic energy loss of the positron and t he larger number of excited electrons. The difference between the distribut ions for the positron and the electron calculated at such low impact energy is due to increasing emission of high-energy electrons excited by the proj ectile without the cascade process; which is more enhanced for the electron s than the positrons. These calculated results are consistent with the rece nt findings based on experiments. (C) 2000 Elsevier Science B.V. All rights reserved.