The high-spin level structures of the transitional nuclei ${}_{}{}^{191}{}_{}{}^{}\mathrm{Pt}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Pt}$ have been studied by ($\alpha , 3n\gamma$) reactions on enriched Os targets. The measurements included $\gamma$-ray singles, comprehensive $\gamma -\gamma$ coincidences, half-life determinations, and $\gamma$-ray angular distributions. The extensive ${}_{}{}^{191}{}_{}{}^{}\mathrm{Pt}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Pt}$ level schemes established are reported here. In both nuclei, decoupled $\nu {i_{\frac{13}{2}}}^{-1\mathrm{}}$ bands, strongly resembling the ground bands of the adjacent core nuclei, and many other high-spin positive parity states have been located. Low-lying $\frac{21}{2^{-}}$ bands have also been observed in both nuclei and they are described as semidecoupled bands with microscopic structures dominated by three-quasiparticle components of the type ($\nu {i_{\frac{13}{2}}}^{-2\mathrm{}}, \nu j^{-1\mathrm{}}$). The abundant information about $\nu i_{\frac{13}{2}}$ level families obtained in these experiments and in a complementary ${}_{}{}^{191}{}_{}{}^{}\mathrm{Au}$ decay study is discussed, and it is shown that these complex level spectra can be accounted for rather well in terms of the coupling of an $i_{\frac{13}{2}}$ neutron hole to a triaxially deformed core.

NUCLEAR REACTIONS ${}_{}{}^{190}{}_{}{}^{}\mathrm{Os}$, ${}_{}{}^{192}{}_{}{}^{}\mathrm{Os}(\alpha , 3n\gamma )$, $E=31-46\mathrm{}$ MeV; measured $E_{\gamma }$, $I_{\gamma }\left(\theta \right)$, $\gamma -\gamma$ coin, $T_{\frac{1}{2}}$; ${}_{}{}^{191,193}{}_{}{}^{}\mathrm{Pt}$ deduced level schemes, $J$, $\pi$.

• Received 27 August 1976

DOI:https://doi.org/10.1103/PhysRevC.15.94