Photoionization of two electrons in helium

Abstract

Cross sections for ionization of two electrons in helium by high-energy photons have been evaluated using many-body perturbation theory. All lowest-order amplitudes [from the effects of shakeoff, ground-state correlation, and the absorption of a photon by one electron, which then hits another electron (two-step 1)] are included. At a photon energy of 2.8 keV our calculated ratio of double- to single-ionzation cross sections is 1.6%, in agreement with a very recently observed value of 1.6\ifmmode\pm\else\textpm\fi{}0.3%.