Photoabsorption and Compton scattering in ionization of helium at high photon energies

Production of singly and doubly charged helium ions by impact of keV photons is studied. The ratio Rph=σ++ph/σ+ph for photoabsorption is calculated in the photon‐energy range 2–18 keV using correlated initial‐ and final‐state wave functions. Extrapolation towards asmptotic photon energies yields Rph(ω→∞)=1.66% in agreement with previous predictions. Ionization due to Compton scattering, which becomes comparable to photoabsorption above ω∼3 keV, is discussed