Evidence for Hindered First-Forbidden Unique Beta Branch inCa47Decay

An upper limit of (9.8±1.5)×${10}^{-4\mathrm{}}$ per decay for the intensity of the first-forbidden unique beta transition from the ${\frac{7}{2}}^{-}$ ground state in ${\mathrm{Ca}}^{47}$ to the ${\frac{3}{2}}^{+}$, 767.2-keV hole state in ${\mathrm{Sc}}^{47}$, has been determined, by Ge(Li) spectrometry, as the difference between feed-out and feed-in gamma intensities. Gammas observed are [keV, ${10}^4$× intensity per decay]: [530.6±0.5, 9.6±0.9], feed-in; and [767.2±0.5, 19.4±1.4], feed-out. However, the sum of the upper intensity limits observable for feed-in gammas from seven known higher energy levels in ${\mathrm{Sc}}^{47}$ is four times higher than the above difference, which can thus be stated only as a limit to the beta intensity. This limit corresponds to $log{f}_{1}t\ge 9.5\pm 0.2$, a slow first-forbidden unique case similar to the analogous decay in ${\mathrm{Ca}}^{45}$, for which $log{f}_{1}t=9.2\mathrm{}$. From the intensities (limits) observed for gammas from all levels to those certainly populated in ${\mathrm{Ca}}^{47}$ decay (767.2, 807.9 and 1297.0 keV), $log\mathrm{ft}$ lower limits are obtained, ranging from 6.6 to 9.2, for these higher states.