Separation of Photoabsorption and Compton Scattering Contributionsto He Single and Double Ionization

Abstract

We have experimentally separated the contributions of photoabsorption and Compton scattering to He single and double ionization for high-energy photon impact by measuring the full momentum vector of the recoiling ${\mathrm{He}}^{1+,2+}$ ions. For recoil ions following photoabsorption large momenta and a distinct dipole emission pattern are observed. The ions produced by Compton scattering show small momenta. For the ratio of double to single ionization we find $(1.22\ifmmode\pm\else\textpm\fi{}0.06)$% at ${8.8}_{\ensuremath{-}1.65}^{+1.5}$ keV for Compton scattering and $(1.72\ifmmode\pm\else\textpm\fi{}0.12)$% at ${7.0}_{\ensuremath{-}1.6}^{+2.1}$ keV for photoabsorption. We compare our data with recent theories.