Measurements of double differential cross sections in electron impact ionization of helium and argon

Abstract

Double differential cross sections (angular distributions and energy loss spectra) have been measured of electrons after ionizing electron collisions with helium at primary energiesE ₀ between 25 eV and about 260 eV and with argon atE ₀=75, 150 and 200 eV. The spectra have been measured with an energy analyzing collector system of constant transmission. It was found that for high collision energies (E ₀≧ 80 eV) the outgoing electrons belong to one of the two energetically well separated groups, either thefast electrons, which are scattered mainly in forward direction or theslow electrons which are distributed isotropically into all angles. At low primary energiesE ₀ no separation into groups is possible. Several findings indicate the qualitative applicability of the binary collision model.