Cross Sections for Singly Differential and Total Ionization of Helium by Electron Impact

Authors

Yong-Ki Kim, National Institute of Standards and Technology, Gaithersburg, Maryland
Walter R. Johnson, Department of Physics, University of Notre Dame, Notre Dame, Indiana
M. Eugene Rudd, University of Nebraska - LincolnFollow

Date of this Version

2000

Comments

Published in Physical Review A Volume 61, 2000. Copyright © American Physical Society; used by permission.

Abstract

The binary-encounter dipole (BED) model for electron-impact ionization is applied to helium using the continuum dipole oscillator strength calculated from the relativistic random-phase approximation. The resulting total ionization cross section agrees with available experimental data well within the quoted experimental uncertainties. The singly differential (=energy distribution of ejected electrons) cross section agrees well in shape with available experiments. Because of the remarkable agreement with experiment at all incident and ejected electron energies and the compact analytic form of the cross sections, we propose that the BED cross sections for helium serve as a normalization standard with an accuracy of ±5% from the threshold to 1 keV in the primary electron energy.