The energy spectrum of $K$ electrons ejected from ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$ during $K$-capture decay has been measured in the energy range from 5 to 180 keV. In addition, a value of the total $K$-shell internal ionization probability per $K$ capture has been estimated experimentally. The phenomenon was observed by the triple-coincidence ($K$-x-ejected $e^{-}-K$-x) experiment using a gas proportional counter for ejected electrons and two gas proportional counters for Mn $K$ x rays. For the higher-energy region of ejected electrons, the confinement of the electrons within the sensitive volume of the electron counter was achieved by applying a magnetic field. The $L$-shell contributions were rejected completely by the triple-coincidence technique. A fairly good agreement between our measured spectrum and theoretical curves, recently calculated relativistically by the present authors and by Intemann, is established even in the low-energy region down to 5 keV. The total ionization probability also agrees with the theoretical predictions within experimental error.

RADIOACTIVITY ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$; measured energy spectrum of ejected $K$ electrons from 5 to 180 keV and total ionization probability.

• Received 11 November 1974

DOI:https://doi.org/10.1103/PhysRevC.11.920