Four-valence-proton yrast states inEr8268150

The level structure of the four-valence-proton $N=82\mathrm{}$ nucleus ${}_{}{}^{150}{}_{}{}^{}\mathrm{Er}$ has been studied by $\gamma$-ray spectroscopy following reactions of 225-255 MeV ${}_{}{}^{58,60}{}_{}{}^{}\mathrm{Ni}$ beams on ${}_{}{}^{92,94,95}{}_{}{}^{}\mathrm{Mo}$ and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ targets. Yrast levels in ${}_{}{}^{150}{}_{}{}^{}\mathrm{Er}$ are established up to 9.5 MeV excitation energy; they include isomeric levels at 2797, 7372, and 9509 keV. The observed levels up to 5222 keV are interpreted in terms of shell model configurations involving the four valence protons outside the ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ core. They include states with dominant seniority two and four configurations ${\pi h}_{\frac{11}{2}}^4$, ${\pi h}_{\frac{11}{2}}^3{s}_{\frac{1}{2}}$, and ${\pi h}_{\frac{11}{2}}^3{d}_{\frac{3}{2}}$, and octupole excitations. The levels above 5222 keV must involve excitation of the ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ core, and they are not interpreted in detail. The energies of the ${\pi h}_{\frac{11}{2}}^4$ levels are found to agree reasonably with predictions based on empirical two-body interactions taken from the ${\pi h}_{\frac{11}{2}}^2$ spectrum of ${}_{}{}^{148}{}_{}{}^{}\mathrm{Dy}$. Even better agreement is obtained by taking account also of the known ${\pi h}_{\frac{11}{2}}^3$ energies in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ho}$. The dependence of $E2\mathrm{}$ transition probabilities in $N=82\mathrm{}$ nuclei on the ${\pi h}_{\frac{11}{2}}$ subshell occupation number is discussed.