Mean Lifetimes and Branching Ratios of Low-Lying Levels inS33

The mean lifetimes of the levels of ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ below 3.3-MeV excitation energy have been measured by the Doppler shift attenuation method. The ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}(\alpha ,n){}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ reaction was used to populate these states. Si${\mathrm{O}}_2$ targets (enriched to 95% in ${}_{}{}^{33}{}_{}{}^{}\mathrm{Si}$) evaporated onto Ni backings were bombarded with $\alpha$-particles ranging in energy 5.5-9.0 MeV. $\gamma$-ray spectra were recorded with a 20-cc Ge (Li) detector at 0°, 90°, and 510° to the beam. The following mean lifetimes were found: $\tau (0.842\mathrm{}-\mathrm{MeV}\mathrm{level})=1.66\mathrm{}\pm 0.34$ psec, $\tau \mathrm{}\left(1.968\right)=182\mathrm{}\pm 22$ fsec, $\tau \mathrm{}\left(2.313\right)=183\mathrm{}\pm 25$ fsec, $\tau \mathrm{}\left(2.869\right)<15\mathrm{}$ fsec, $\tau \mathrm{}\left(2.937\right)>4\mathrm{}$ psec, $\tau \mathrm{}\left(2.970\right)=82\mathrm{}\pm 12$ fsec, $\tau \mathrm{}\left(3.221\right)<65\mathrm{}$ fsec. The branching ratios of the 2.970-MeV level were determined to be (90±5)% to the ground state and (10±5)% to the second excited state.