Two-electron ejection from helium by Compton scattering

Double ionization of the ground state of helium by Compton scattering is investigated using many-body perturbation theory. Representative calculations of cross sections differential in the scattered photon energy and angle are given to illustrate the nature of the process. Total cross sections for single ionization and double ionization of helium and the ratio of these cross sections are presented for energies from 2.5 to 20 keV. Current experimental data for the ratio due to both Compton scattering and photoionization are in reasonable agreement with the corresponding calculations presented here. However, comparisons of the present results with other calculations reveal substantial discrepancies. Possible reasons for these differences at finite energies are proposed. Our results for double ionization by Compton scattering have not reached an asymptotic limit.