The lifetimes of three low-lying excited states in ${}_{}{}^{117}{}_{}{}^{}\mathrm{In}$ have been measured by delayed-coincidence techniques using a time-to-amplitude converter. These states at 748, 659, and 587 keV are fed by ${\beta }^{-}$ decay from the $s_{\frac{1}{2}}$ ground state of ${}_{}{}^{117}{}_{}{}^{}\mathrm{Cd}$ (2.4 h). The measured half-lives are 4.6±0.3, 59.7±2.0, and 0.17±0.03 nsec, respectively. All three levels de-excite directly to the 314-keV $p_{\frac{1}{2}}$ isomeric state but not to the $g_{\frac{9}{2}}$ ground state of ${}_{}{}^{117}{}_{}{}^{}\mathrm{In}$. A comparison of the partial half-lives with the corresponding single-particle estimates has been performed assuming $E1\mathrm{}$, $M1\mathrm{}$, or $E2\mathrm{}$ character for the transitions. Higher multipolarities are ruled out by the short half-lives of the levels. $\mathrm{Log}\mathrm{ft}$ values of transitions from ${}_{}{}^{117}{}_{}{}^{}\mathrm{Cd}$ indicate negative parities for the three levels, and systematics of known $\gamma$-ray transition probabilities suggest $M1-E2\mathrm{}$ character for all the transitions involved in their de-excitation. However, when considered as pure $E2\mathrm{}$, the transitions from the 748- and 659-keV levels are delayed by factors ranging from about 3 to 20 compared with the single-particle transition probabilities, whereas when they are considered as pure $M1\mathrm{}$ transitions, delays of the order of ${10}^4$ result. On the other hand, the 274-keV transition from the 587-keV level is enhanced by a factor of about 60 when assumed as pure $E2\mathrm{}$. The possibility of considering this level as a member of the doublet obtained by coupling the $2^{+}$ phonon excitation of the ${}_{}{}^{116}{}_{}{}^{}\mathrm{Cd}$ or ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$ even-even core to the $p_{\frac{1}{2}}$ single-particle state is discussed.

• Received 28 August 1967

DOI:https://doi.org/10.1103/PhysRev.168.1409