Decays of 2.45-hTam178and 23.8-minLum178to theKπ=8−levels inHf178

The decays of the high-spin isomers of ${}_{}{}^{178}{}_{}{}^{}\mathrm{Ta}$ (2.45 h) and ${}_{}{}^{178}{}_{}{}^{}\mathrm{Lu}$ (23.8 min) to the two strongly admixed $K^{\pi }=8^{-}$ states in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ were reinvestigated. The main features of the previously reported decay schemes are confirmed and several long-standing ambiguities are resolved. The results of this investigation indicate that the 1147-keV level is largely the two-neutron state and the 1479-keV level is largely the two-proton state in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$. They are found to be 34% admixed with one another. This mixing value is in good agreement with the value deduced from the $\frac{M1\mathrm{}}{E2\mathrm{}}$ cascade ratios of the 1147-keV band and from the comparison of the $E1\mathrm{}$ ($\nu =7\mathrm{}$) hindrance factors of these two states in this mass region. The band-mixing matrix element for these two states was found to be in agreement with the recent theory which introduces the residual neutron-proton interaction to account for the mixing. The spin-parity of ${}_{}{}^{178}{}_{}{}^{}\mathrm{Lu}_{}^m{}_{}{}^{}$ (23.8 min) was deduced to be $K^{\pi }=9^{-}$ with a possible Nilsson configuration of $\frac{9}{2^{-}}{\mathrm{}\left[514\right]\mathrm{}}_p$, $\frac{9}{2^{+}}{\mathrm{}\left[624\right]\mathrm{}}_n$.