Direct double L-shell ionization of a Be-like ion by a high-energy photon

Abstract

We have evaluated the cross sections for the double L-shell ionization of a Be-like ion by a single high-energy photon. The evaluation is performed within the framework of non-relativistic perturbation theory with respect to the interelectron interaction. The correct linear combination of the 2s2- and 2p2-configurations is used as zeroth approximation for the wavefunction of the initial state. The interelectron interaction is taken into account between the valence electrons, while the electrons of the inner K-shell are considered as spectators. The scaling formula is obtained for the ratio of double-to-single ionization cross sections. As a by-product of our approach, we have also derived the analytical expression for the Auger width of the lowest doubly excited state of a He-like multicharged ion.