Double K-shell ionization in the electron capture decay of ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$

The probability per K capture for double K-shell ionization in the electron capture decay of ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$ was obtained by fitting a model spectrum to the x-ray spectrum recorded to very high statistics in a high-resolution Si(Li) detector. The result, ${\mathit{P}}_{\mathit{K}\mathit{K}}$=(1.3±0.2)×${10}^{\mathrm{-}4}$, confirms the trend wherein experimental data decrease smoothly with Z, and are intermediate between the theoretical predictions of Intemann and of Suzuki and Law. Corrections to some recently published ${\mathit{P}}_{\mathit{K}\mathit{K}}$ values reconcile them with this trend.