EXCITATION-IONIZATION AND DOUBLE-IONIZATION OF HELIUM BY COMPTON-SCATTERING

We investigate the behavior of the cross section for inelastic photon scattering in the limit of high but nonrelativistic photon energies omega --> infinity at helium leading to two-electron transitions. Our calculation employs fully correlated wave functions for the helium ground state and different forms for approximate two-electron final states. We determine the omega --> infinity limit for the ratio of double to single ionization. We find the high-energy behavior to differ significantly from the one for photoabsorption. Our results confirm our previous estimate [Andersson and Burgdorfer, Phys. Rev. Lett. 71, 50 (1993)] but disagree with recent predictions by Hino et al. [Phys. Rev. Lett. 72, 1620 (1994)].