New High-Spin IsomerHf179m2and Intraband Branchings in the Ground-State Rotational Sequence ofHf179

A new high-spin isomer ${}_{}{}^{179m_2}{}_{}{}^{}\mathrm{Hf}$ has been produced by irradiation of isotopically enriched ${}_{}{}^{176}{}_{}{}^{}\mathrm{Yb}$ with $\alpha$ particles. To investigate its decay, Ge(Li) $\gamma$-ray spectra, Si(Li) conversion-electron spectra, and NaI(Tl)-Ge(Li) and Ge(Li)-Ge(Li) $\gamma -\gamma$ coincidence spectra have been recorded. $\gamma$ rays with energies 122.7, 146.2, 169.8, 192.8, 217.0, 236.6, 257.5, 268.9, 316.0, 362.6, 409.8, and 453.7 keV have been attributed to the decay of the isomer. These decay with a half-life of (29±1) day. The coincidence measurements establish that the quanta with energies 122.7 through 236.6 keV are in cascade, while the $\gamma$ rays with energies 268.9 through 453.7 keV represent crossover transitions within a rotational band with levels up to $I=\frac{21}{2}$ built on the ${}_{}{}^{179}{}_{}{}^{}\mathrm{Hf}$ ground state. The rotational-model quantity $\frac{{(g_K-g_R)}^2}{{Q_0}^2}$ has been derived from $\gamma$ intensity measurements of the cascade and crossover transitions. It is constant within the experimental error for all members of the band. The values for the gyromagnetic ratios $g_K=-0.202\mathrm{}\pm 0.027$ and $g_R=0.160\mathrm{}\pm 0.014$ have been deduced.