Double K-shell photoionization of silver

We have investigated double K-shell vacancy production in x-ray photoionization of silver. Measurements were carried out with photon energies (50-90 keV) varying from below threshold to beyond the expected maximum of the double K-shell ionization cross section. The limit of asymptotically high energies was deduced from measurements of double K-shell ionization following K-electron capture by Cd-109 nuclei. The photon energy dependence of the ratio of double to single K vacancies produced is compared to similar measurements in helium and models thereof. The dependence of that ratio on atomic number is assessed by combining these data with previous experimental and theoretical estimates. The results show a clear growth in the relative importance of the dynamical electron-electron scattering contribution in heavy atoms.