Experimental and theoretical momentum transfer dependence of the He (e, 2e) cross section for incident electron energies 150 eV and 488 eV

Abstract

The relative triple differential cross section for the electron impact ionization of helium has been measured and calculated for incident energies of 150 eV and 488 eV, and an ejected electron energy 34.5 eV. At both incident energies coplanar (e, 2e) experiments were carried out for a fixed pair of ejected directions +90°, − 90° and a range of scattering angles −30° → +30°, and also for a fixed pair of ejected directions +75°, − 105° and a range of scattering angles −34° → +18°. The kinematics of these experiments cover a momentum transfer range 0.38 → 3 au. The data are presented directly as pairs of (e, 2e) scattered electron angular distributions, and in the manipulated form of their sum, difference and the ratio difference/sum. These are compared with up to five types of theoretical calculations. Good, but not perfect, agreement is found between experiment and calculations that include significant post-collision interaction effects. All calculations predict an almost identical oscillatory feature, in the difference and ratio of the cross sections, which is observed in the experimental data for incident energy 150 eV and is due to the fact that the cross section passes through zero close to, but not exactly at, 0° scattering.