Probability ofK-Shell Internal Ionization in the Beta Decay ofTc99

The $K$-shell internal ionization probability for the decay of ${}_{}{}^{99}{}_{}{}^{}\mathrm{Tc}$ has been measured using a high-resolution Si(Li) x-ray spectrometer. Absolute source strengths were determined on the basis of source weight and also from an analysis of the intensities of Tc $K$ x rays produced during irradiations with 60-MeV $\alpha$ particles. A value of (3.89 ± 0.16) × ${10}^{-4\mathrm{}}$ per $\beta$ decay was obtained for the $K$-shell internal-ionization probability. This result is compared with the predictions of various theories of electron shakeoff.