A critical evaluation of high energy electron impact spectroscopy to measure Compton profiles

High precision Compton profile measurements on helium and molecular hydrogen obtained by high energy electron impact spectroscopy are presented. Inelastic electron scattering cross sections at 35 keV incident energy have been studied for both He and H2 over the momentum transfer range of 1.5-12.5 au. It is shown that there is a disparity between the energy-loss spectra converted to Compton profiles by means of the binary encounter theory and the theoretical Compton profile. The discrepancy displays itself as an asymmetry of the profile and a shift of the peak to a lower energy loss, known as the 'Compton defect'. A critical evaluation of the technique, improvements made over the previous electron Compton work, the method of data analysis and a rigorous test of the binary encounter theory are discussed in detail. The problem of multiple scattering is also analysed. (author)