Calculation of Double Differential Cross Sections for Ionizing Collisions of Electrons with Helium by Born Approximation and Binary Encounter Theory

Abstract

The double differential cross sections (ddcs's) for secondary electrons resulting from ionizing collisions of electrons with helium atoms have been calculated with three kinds of approximations; the scaled Born approximation, the plane-wave Born approximation, and the binary encounter theory. The energies of incident electrons are 500 eV and 2000 eV, and the energies of secondary electrons are 5∼200 eV. While the ddcs's calculated by the scaled Born approximation excellently well reproduce the experimental ddcs's for 2000 eV electron impact, the discrepancies between theory and experiment are rather remarkably in the low and intermediate energy regions of secondary electrons for 500 eV electron impact. The ddcs's in the intermediate angular range are well reproduced by the binary encounter theory, which also yields the forward rise experimentally observed in the angular distributions. The agreement between the experimental and the plane-wave Born cross sections is very poor in the energy regions of incide...