The decays of 4.2-min ${}_{}{}^{152}{}_{}{}^{}\mathrm{Tb}$, 3.3-min ${}_{}{}^{154}{}_{}{}^{}\mathrm{Ho}$, 11.8-min ${}_{}{}^{154}{}_{}{}^{}\mathrm{Ho}$, and 82-sec ${}_{}{}^{156}{}_{}{}^{}\mathrm{Tm}$ have been studied by $\gamma$-ray and conversion electron spectroscopy using the He-jet technique. High-spin states in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}$ were also studied in the ${}_{}{}^{152}{}_{}{}^{}\mathrm{Sm}$($\alpha$,$4n\gamma$) reaction at 50 MeV and the ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$($\alpha$,$2n\gamma$) reaction at 28 MeV. The systematic behavior of quasirotational bands in $N=88\mathrm{}$ nuclei has been studied, and observed features in the location of $\beta$- and $\gamma$-band states are shown to be explainable from a consideration of available orbitals in a Nilsson diagram. Microscopic calculations employing fourth and sixth order versions of the boson expansion model of Tamura, Kishimoto, and Weeks reproduce the known low-lying positive parity states in ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$, and ${}_{}{}^{156}{}_{}{}^{}\mathrm{Er}$. Experimentally observed negative-parity states are explained remarkably well by a quadrupole-octupole coupling model, but a backbending plot suggests a possible change in intrinsic structure above spin 11.

RADIOACTIVITY ${}_{}{}^{152}{}_{}{}^{}\mathrm{Tb}_{}^m{}_{}{}^{}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Ho}_{}^{m_1}{}_{}{}^{}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Ho}_{}^{m_2}{}_{}{}^{}$, ${}_{}{}^{156}{}_{}{}^{}\mathrm{Tm}$; $I_{\gamma }$, $E_{\gamma }$, $I_{\mathrm{ce}}$, $E_{\mathrm{ce}}$, $\gamma -\gamma$ coin. ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{156}{}_{}{}^{}\mathrm{Er}$ deduced levels, ICC, $J$, $\pi$; systematics, comparison with microscopic theory.

NUCLEAR REACTIONS ${}_{}{}^{152}{}_{}{}^{}\mathrm{Sm}$($\alpha$,$4n$), $E_{\alpha }=50\mathrm{}$ MeV; ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$($\alpha$,$2n$), $E_{\alpha }=28\mathrm{}$ MeV; measured $E_{\gamma }$, $I_{\gamma }$, $I_{\gamma }\left(\theta \right)$, $I_{\mathrm{ce}}$, $\gamma -\gamma$ coin. ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}$ deduced levels, ICC, $J$, $\pi$. Enriched targets, Ge(Li), Si(Li) detectors.

• Received 3 December 1979

DOI:https://doi.org/10.1103/PhysRevC.21.2556