Gamma ray spectroscopic studies of the $\beta$ decay of ${}_{}{}^{160}{}_{}{}^{}\mathrm{Tm}$ have led to the identification of a new 74.5 s isomer in the ${}_{}{}^{160}{}_{}{}^{}\mathrm{Tm}$ nucleus. This isomer is found to emit seven new $\gamma$ rays of 375.8, 738.7, 840.8, 926.7, 1104.1, 1115.8, and 1186.1 keV which populate six new levels in ${}_{}{}^{160}{}_{}{}^{}\mathrm{Er}$ at 765.7, 1128.6, 1230.3, 1316.6, 1505.7, and 1576.0 keV. The 765.7 keV level is the $6^{+}$ member of the ground-state band known from in-beam $\gamma$-ray studies, whereas the 1128.6-, 1316.6-, and 1505.7-keV levels are tentatively assigned as the $4^{+}$, $5^{+}$, and $6^{+}$ members of the $\gamma$ band, respectively. The 1230.3-keV level is proposed as the $4^{+}$ member of the $\beta$ band.

RADIOACTIVITY ${}_{}{}^{160}{}_{}{}^{}\mathrm{Tm}$ [from ${}_{}{}^{164}{}_{}{}^{}\mathrm{Er}$(p,5n)]; measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $\gamma -\gamma$ coin; deduced ${}_{}{}^{160}{}_{}{}^{}\mathrm{Er}$ levels. Enriched ${}_{}{}^{164}{}_{}{}^{}\mathrm{Er}$ target, intrinsic Ge detectors.

• Received 1 March 1983

DOI:https://doi.org/10.1103/PhysRevC.28.2118