High-accuracy (e, 2e) cross sections for helium: reference data in the first Born approximation

Abstract

The authors present new high-accuracy (6-7%) absolute measurements of the triple differential cross sections for ionisation of helium by 4 and 8 keV electron impact, obtained at small ejected-electron energies and small and intermediate momentum transfer values. When reduced to generalised oscillator strengths, the 4 and 8 keV data are indistinguishable from each other. Also, comparison is made with the three most recent and accurate first Born calculations, and it is concluded that this approximation is certainly valid under the present kinematics. The authors therefore suggest that these data should be used as a standard against which future lower-energy calculations should be calibrated.