The level structure of ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$ has been studied using the ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}(n,\gamma )$ reaction with both thermal and 2-keV neutrons. Measurements of $\gamma$-ray energies and intensities were made using Ge(Li) detectors. From these data a neutron separation energy of 7464.8±0.5 keV has been determined for ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$. A level scheme is proposed for ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$ which contains 47 excited states, with identified de-excitation modes, below 2.35 MeV. Features of the proposed level scheme include: the $K^{\pi }=2^{-},0^{-}, \mathrm{and} 3^{-}$ octupole-vibrational bands with band-head energies of 1318, 1710, and 1851 keV, respectively; the $\gamma$-vibrational band at 1634 keV; three excited $K^{\pi }=0^{+}$ bands with band-head energies of 1487, 1885, and 2100 keV; and, several two-quasiparticle bands with band-head energies in keV (and $K^{\pi }$ assignments) of 1660($3^{+}$), 1624($1^{+}$), 2016($3^{+}$), and 2049($3^{-}$). Configuration assignments for these two-quasiparticle bands are discussed. The available data for the $K^{\pi }=3^{+}$ band at 1606 keV are not inconsistent with the assumption that it has collective character; and it is suggested that it, together with the lowest-lying $3^{+}$ band in ${}_{}{}^{172}{}_{}{}^{}\mathrm{Yb}$ (at 1172 keV), might represent, in the framework of the interacting boson approximation model, examples of $g$-boson excitations.

NUCLEAR REACTIONS ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}(n,\gamma )$, $E=\mathrm{thermal}$, 2 keV; measured $E_{\gamma }$, $I_{\gamma }$; ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$ deduced levels, $J$, $\pi$. Enriched targets, Ge(Li) detectors.

• Received 29 July 1980

DOI:https://doi.org/10.1103/PhysRevC.23.153