Study ofO18Levels withEx<8MeV Using theF19(t,αγ)O18Reaction

Levels in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ were populated with the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(t,\alpha ){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ reaction. Extensive data were collected with good $\alpha$-particle energy resolution (40 keV) at $E_t=2.4\mathrm{}$ MeV, using a computer based data acquisition system. Reaction-produced $\alpha$ particles were detected near 180° in a solid-state annular counter and $\gamma$ radiation was detected in a 10.2×10.2-cm NaI(Tl) crystal at detection angles in the interval $0^{\circ }\le {\theta }_{\gamma }\le {90}^{\circ }$. Multiparameter data collection techniques were used to store the matrix of particle-$\gamma$ pulse-height pairs for coincident events. Angular correlations of $\gamma$ rays from levels with $E_x<8\mathrm{}$ MeV were extracted from these data from which level spins, together with $\gamma$-ray branching ratios and $\gamma$-ray multipole mixing ratios, were deduced. Results include the spin assignments $J=1\mathrm{}$ for the 6.19-MeV level, $J=0\mathrm{}\left(1\right)\mathrm{}$ for the 6.86-MeV level, $1\le J\le 4$ for the 7.75-MeV level, and $1\le J\le 5$ for the 7.96-MeV level. Some new $\gamma$-ray decay modes were found. The 7.96-MeV level decays 67% to the 1.98-MeV level, 12% to the 5.09-MeV level, and 21% to the 5.37-MeV level. The 7.75-MeV level decays 50% to the 1.98-MeV level, 11% to the 4.45-MeV level, and 39% to the 5.09-MeV level. The 6.86-MeV level decays 100% to the 4.45-MeV level. The 6.19-MeV level decays 88% to the ground state, 6% to the 4.45-MeV level, and 6% to either the 5.25- or 5.33-MeV level. The 6.34-MeV level decays 35% to the 1.98-MeV level, 53% to the 3.91-MeV level, and 11% to the 4.45-MeV level. A number of $\gamma$-ray multipole mixing ratios are also reported. For the 7.10-MeV level, $\frac{{\Gamma }_{\gamma }}{{\Gamma }_{\alpha }}$ was found to be 0.9 ± 0.1. These results are compared with predictions of the model due to Ellis and Engeland.