$\gamma$ rays from levels in ${}_{}{}^{147,149,151}{}_{}{}^{}\mathrm{Eu}$ have been studied using primarily (${}_{}{}^{6,7}{}_{}{}^{}\mathrm{Li},xn\gamma$) reactions. Prompt and delayed $\gamma -\gamma$ coincidences, excitation functions, and angular distributions were used to study the in-beam $\gamma$ rays. Bands with $\Delta I=2\mathrm{}$ built on an ${11/2}^{-}$ isomeric state have been observed in all three nuclei and since the energy spacings strongly resemble those of the core nuclei they are interpreted as decoupled bands. The maximum spin observed in the decoupled band is ${27/2}^{-}$ for ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ and ${23/2}^{-}$ for ${}_{}{}^{149,147}{}_{}{}^{}\mathrm{Eu}$. Possible unfavored states associated with the $\pi h_{\frac{11}{2}}$ system have also been identified. High spin positive parity states have been observed for ${}_{}{}^{147}{}_{}{}^{}\mathrm{Eu}$ and ${}_{}{}^{149}{}_{}{}^{}\mathrm{Eu}$. The maximum spin observed for each nucleus is (${33/2}^{+}$) at 4178.1 keV for ${}_{}{}^{147}{}_{}{}^{}\mathrm{Eu}$, (${29/2}^{+}$) at 3042.0 keV for ${}_{}{}^{149}{}_{}{}^{}\mathrm{Eu}$, and (${27/2}^{-}$) at 2118.9 keV for ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$. The experimental results for the negative parity bands of ${}_{}{}^{149,151}{}_{}{}^{}\mathrm{Eu}$ have been compared with predictions of the triaxial rotor plus particle model incorporating a variable moment of inertia. The results of the model calculations give some indication of triaxial shapes for ${}_{}{}^{149}{}_{}{}^{}\mathrm{Eu}$ and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ although the predictions for the symmetric case are not significantly different from those of the asymmetric case.

[NUCLEAR REACTIONS ${}_{}{}^{143,145}{}_{}{}^{}\mathrm{Nd}({}_{}{}^7{}_{}{}^{}\mathrm{Li},3n\gamma )$, ${}_{}{}^{146,148}{}_{}{}^{}\mathrm{Nd}({}_{}{}^6{}_{}{}^{}\mathrm{Li},3n\gamma )$, $E=26.0-34.0\mathrm{}$ MeV; ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},4n\gamma )$, $E=60, 63$ MeV; measured $\sigma (E,E_{\gamma },\theta )$, $\gamma -\gamma$ coin, $\gamma -\gamma$ delay. ${}_{}{}^{147,149,151}{}_{}{}^{}\mathrm{Eu}$ deduced levels, $J, \pi$. Enriched targets. Ge(Li) detectors. Triaxial rotor-plus-particle calculations including VMI.]

• Received 7 March 1977

DOI:https://doi.org/10.1103/PhysRevC.16.227