The angular and energy distributions of ejected electrons in electron-impact ionization of helium

The angular and energy distributions of ejected electrons in the direct He(e,2e)He+ reaction are studied. It is shown that the first Born approximation is applicable for the description of ejected electrons for incident electron energies E0≥500 eV at arbitrary ejection angles. Furthermore, it is shown that the anisotropy of ejected electrons and the predominance of higher order multipole terms give rise to differences in the angular distributions of double differential cross sections for different kinematic conditions. 23 refs.; 9 figs.; 3 tabs