The ($p,t$) reaction at $E_p=19.0\mathrm{}$ MeV has been used to study five isotopes of Os ($A=190, 188, 184, 187, 185$) which lie in a transition region between the deformed rare earths and spherical nuclei. Cross sections and angular distributions have been measured to states up to about 2 MeV of excitation in all cases except ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}$ and ${}_{}{}^{190}{}_{}{}^{}\mathrm{Os}$ in which states were seen up to 4 MeV. The energies of the $J^{\pi }=0^{+}$ states which we see and their summed cross sections in percent of the ground state (in parenthesis) are: 913 (4.7), 1551 (1.8), and 1734 keV (6.3) in ${}_{}{}^{190}{}_{}{}^{}\mathrm{Os}$, 1087 (5.7), 1480 (3.7), 1705 (1.2), and 1765 keV (<1) in ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}$, and 1042 (8.4) and tentatively 1982 (1.2) and 2268 keV (1.3) in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Os}$. The $L=0\mathrm{}$ transitions seen in the odd isotopes are at 9.8, 77, 730, and 1657 keV in ${}_{}{}^{187}{}_{}{}^{}\mathrm{Os}$ and 1070 and 1213 keV in ${}_{}{}^{185}{}_{}{}^{}\mathrm{Os}$. The results show no positive evidence for the existence of strongly populated shape isomeric $0^{+}$ states similar to those seen in the transition region around $N=88\mathrm{}$. In ${}_{}{}^{188,190}{}_{}{}^{}\mathrm{Os}$ and possibly ${}_{}{}^{192}{}_{}{}^{}\mathrm{Os}$ the lowest exicted $K=0\mathrm{}$ and $K=4\mathrm{}$ bands have the properties expected for two phonon $\gamma$ vibrations. In addition to the rotational excitations in the odd isotopes, two strong transitions have been seen to states at 599 and 802 keV in ${}_{}{}^{185}{}_{}{}^{}\mathrm{Os}$ which we have postulated to be the $|K_0\pm 2|\gamma$ vibrations based on the ${1/2}^{-}$ [510] state with admixed one quasiparticle components. Similar states have been seen in ${}_{}{}^{187}{}_{}{}^{}\mathrm{Os}$. The lowest $L=0\mathrm{}$ transfers to states in ${}_{}{}^{185,187}{}_{}{}^{}\mathrm{Os}$ were found to have significantly lower intensity than the ground states in the adjacent even-$N$ nuclei. In the case of ${}_{}{}^{187}{}_{}{}^{}\mathrm{Os}$ the low lying $L=0\mathrm{}$ strength is split between two states. Calculations have been made to understand these phenomena in terms of blocking effects and Coriolis mixing.

NUCLEAR REACTIONS ${}_{}{}^{192,190,186,187,189}{}_{}{}^{}\mathrm{Os}\mathrm{}(p,t)\mathrm{}$, $E_p=19\mathrm{}$ MeV; measured $\sigma \left(\theta \right)$; deduced ${}_{}{}^{190,188,184,185,187}{}_{}{}^{}\mathrm{Os}$ levels, $J^{\pi }$; pairing plus DWBA calculations, comparison with expt. for lowest $L=0\mathrm{}$ states.

• Received 22 December 1975

DOI:https://doi.org/10.1103/PhysRevC.13.2288