Helium ionization with excitation of the atom accompanied by absorption and scattering of high-energy photons

We calculate analytically the cross sections for ionization of the helium atom with absorption and scattering of high-energy photons. The electrons are assumed to be moving in the Coulomb field of the nucleus. The electron-electron interaction is taken into account in the first order of perturbation theory. The high-frequency limits for the ratios of these cross sections to the single-electron ionization cross sections are obtained for s-excitations in absorption and for s- and p-excitations in scattering. (C) 1997 American Institute of Physics.