Yrast states in ${}_{}{}^{156}{}_{}{}^{}\mathrm{Yb}$ have been identified to spin and parity $J^{\pi }={25}^{-}$ at 7405 keV using the ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},4n){}_{}{}^{156}{}_{}{}^{}\mathrm{Yb}$ ($E=70\mathrm{}-120$ MeV) and ${}_{}{}^{113}{}_{}{}^{}\mathrm{In}({}_{}{}^{46}{}_{}{}^{}\mathrm{Ti},p2n){}_{}{}^{156}{}_{}{}^{}\mathrm{Yb}$ ($E=190\mathrm{}-210$ MeV) reactions together with standard $\gamma$-ray spectroscopic techniques. Evidence was found for additional transitions extending to $J-30$ at 9464 keV. One isomeric state was observed with $J^{\pi }={11}^{-}$ at $E_x=3028\mathrm{}$ keV, having $T_{\frac{1}{2}}=6.0\mathrm{}\pm 0.5$ ns. The structure of this nucleus is compared with that of other $N=86\mathrm{}$ isotones. It appears that most of the features can be described in terms of relatively simple shell model configurations in a nearly spherical ($\left|\beta \right|\lesssim 0.1$) potential.

NUCLEAR REACTIONS ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},4n){}_{}{}^{156}{}_{}{}^{}\mathrm{Yb}$ $E=70\mathrm{}-120$ MeV; ${}_{}{}^{113}{}_{}{}^{}\mathrm{In}({}_{}{}^{46}{}_{}{}^{}\mathrm{Ti},p2n){}_{}{}^{156}{}_{}{}^{}\mathrm{Yb}$ $E=190\mathrm{}-210$ MeV. Measured $E_{\gamma }$, $I_{\gamma }$, linear polarizations, $\gamma -\gamma$, $\gamma$-x-ray, $\gamma$-charged particle coincidences, pulsed beam lifetimes. Deduced level energies, branching ratios, spin and parity assignments, multipole mixing ratios, electromagnetic transition strengths. Ge(Li) detectors. Enriched targets. Comparison with systematic trends.

• Received 24 October 1980

DOI:https://doi.org/10.1103/PhysRevC.23.2078