V. A. Yerokhin,
A. Surzhykov,
and S. Fritzsche

Phys. Rev. A,

**Relativistic calculations of double K-shell-photoionization cross sections for neutral medium-Z atoms**Phys. Rev. A,

**90**:063422 (December 2014)## 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's-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.