Electron-Capture-to-Positron Ratio inBi207Decay

Positron emission in the second-forbidden nonunique transition from the ground state of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ to the first excited level of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ was found to occur in (1.2 ± 0.2) × ${10}^{-4\mathrm{}}$ of all decays. Taking into account newly assigned relative intensities of the ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ electron-capture decay branches, the $\frac{\mathrm{EC}}{{\beta }^{+}}$ ratio is found to be (6 ± 1) × ${10}^2$. From the ${\beta }^{+}$ intensity and the measured ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ half-life of 38 ± 4 yr, it follows that $logft=12.6\mathrm{}\pm 0.1$ for this transition.