Relativistic calculations of double $K$-shell photoionization for neutral medium-$Z$ atoms

TL;DR

This paper presents fully relativistic calculations of double K-shell photoionization cross sections for neutral medium-Z atoms, incorporating multipole effects and electron-electron retardation, validated against experimental data.

Contribution

It introduces a gauge-invariant, Green-function based relativistic method for calculating double K-shell ionization, covering a range of medium-Z atoms and including all photon multipoles.

Findings

Calculated cross section ratios agree with experimental data.

Method accounts for all photon multipoles and electron-electron retardation.

Provides comprehensive relativistic data for medium-Z atoms.

Abstract

Fully relativistic calculations are presented for the double $K$-shell photoionization cross section for several neutral medium-$Z$ atoms, from magnesium ($Z = 10$) up to silver ($Z = 47$). The calculations take into account all multipoles of the absorbed photon as well as the retardation of the electron-electron interaction. The approach is based on the partial-wave representation of the Dirac continuum states and uses the Green-function technique to represent the full Dirac spectrum of intermediate states. The method is strictly gauge invariant, which is used as an independent cross check of the computational procedure. The calculated ratios of the double-to-single $K$-shell ionization cross sections are compared with the experimental data and with previous computations.