Electron impact ionisation of helium at intermediate energies

Electron ionisation of helium at energies between 40 and 400 eV has been studied using a distorted-wave model based upon the assumption that the slower outgoing particle fully screens the residual ion. The model employs a consistent and elaborate description of all the channels involved. It appears that the present exchange model DWE agrees well with the measurements of the integrated ionisation cross section by Montague et al (1984). The differences between DWE and experiment are of the same order of magnitude as the differences obtained by Campeanu et al (1987) in the positron impact case.