Double K-shell vacancy production in the electron capture decay of 139Ce.

Abstract

The probability of double K-shell vacancy production in the electron capture decay of $^{139}\mathrm{Ce}$ to the 166-keV level of $^{139}\mathrm{La}$ has been investigated. Triple coincidences between the 166-keV gamma ray, the La satellite K\ensuremath{\alpha} x ray, and the La hypersatellite K\ensuremath{\alpha} x ray were measured using two intrinsic Ge detectors. We looked for the sum of two of the three radiations in one detector in coincidence with the third radiation in the other detector. The probability of double K-shell vacancy production per K-shell electron capture (${\mathit{P}}_{\mathit{K}\mathit{K}}$) was found to be (2.0\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$. From this and the known ${\mathit{P}}_{\mathit{K}\mathit{K}}$ for $^{131}\mathrm{Cs}$ we estimate a probability for zero K-shell vacancy production (shakedown) per K-shell electron capture of \ensuremath{\lesssim}2.4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ for $^{139}\mathrm{Ce}$.