Energy Spectrum of Atomic Electrons Ejected in Electron-Capture Decay ofFe55

The shape of the energy spectrum of orbital electrons ejected from ${\mathrm{Fe}}^{55}$ during nuclear decay by electron capture has been measured from 28 to 190 keV (the theoretical end point is at 218 keV). The electrons were detected in a proportional counter or in a semiconductor particle detector, in coincidence with Mn $K$ x rays. The electron ejection probability decreases by a factor of ${10}^3$ over the investigated energy range. The shape of the measured spectrum differs somewhat from theoretical predictions, in that the ejection probability falls off more slowly with energy. The discrepancy becomes more pronounced with decreasing energy. The contributions of $L$-electron ejection are considered.