Levels in ${}_{}{}^{20}{}_{}{}^{}\mathrm{O}$ populated in the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}\mathrm{}(t,p)\mathrm{}{}_{}{}^{20}{}_{}{}^{}\mathrm{O}$ reaction have been studied at bombarding energies of 10 and 12 MeV using proton-γ angular correlation measurements in an axially symmetric geometry. Spin assignments have been made to levels at 1.67 MeV ($J^{\pi }=2^{+}$) and 4.06 MeV ($J^{\pi }=2^{+}$). The angular correlations measured for levels at $E_x=4.45\mathrm{} \mathrm{and} 5.38$ MeV are consistent with $J^{\pi }=0^{+}$ for both. The $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratio for the 4.06 → 1.67 MeV transition is measured as $\delta =-0.18\mathrm{}\pm 0.08$. Comparison of relative electromagnetic matrix elements (obtained from mixing ratio and branching ratio measurements) with the predictions of shell model calculations suggests that excitations out of the $1p$ shell play a role in describing these transitions. The population parameters measured for the ($t,p$) reaction leading to the first excited states of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{20}{}_{}{}^{}\mathrm{O}$ show that at $E_t=12\mathrm{}$ MeV the reaction mechanism is predominantly direct.

NUCLEAR REACTIONS ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}(t,p\gamma ){}_{}{}^{20}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(t,p\gamma ){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, $E=10,12$ MeV, measured $\sigma \left(E_p\right)$, $p\gamma \left(\theta \right)$, $E_{\gamma }$. ${}_{}{}^2{}_{}{}^{}\mathrm{O}$ deduced levels, $J$, $\pi$, $\delta$, branching ratios.

• Received 22 August 1980

DOI:https://doi.org/10.1103/PhysRevC.23.980