A previously unreported isotope, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Tb}$, has been identified, and its half-life has been measured to be 2.11±0.10 min. This activity was observed in the Tb fraction separated, using a high-performance liquid chromatograph, from the fission products resulting from spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$. Some 24 $\gamma$ rays have been associated with the ${}_{}{}^{165}{}_{}{}^{}\mathrm{Tb}$ decay, ∼16 of which have been placed in a level scheme for ${}_{}{}^{165}{}_{}{}^{}\mathrm{Dy}$. New features of the ${}_{}{}^{165}{}_{}{}^{}\mathrm{Dy}$ level scheme are excited states at 1337.1, 1400.2, 1773.1, and possibly 1813.7 keV, which are fed by $\beta$ transitions with $log\mathrm{ft}$ values between 5.1 and 5.7. Configuration assignments for these states are discussed.

RADIOACTIVITY ${}_{}{}^{165}{}_{}{}^{}\mathrm{Tb}$, measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$; ${}_{}{}^{165}{}_{}{}^{}\mathrm{Dy}$ deduced levels $J$, $\pi$, $log\mathrm{ft}$. Radiochemical separation, Ge(Li) detectors.

• Received 9 August 1982

DOI:https://doi.org/10.1103/PhysRevC.27.1266