P31(He3,pγ)S33andK39(He3,pγ)Ca41Reactions and theγDecay of Analog States inS33andCa41

Proton-$\gamma$-ray coincidence measurements have been made on the reactions ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}({}_{}{}^3{}_{}{}^{}\mathrm{He},p\gamma ){}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}({}_{}{}^3{}_{}{}^{}\mathrm{He},p\gamma ){}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$ at incident ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ energies of 12 and 13 MeV. The protons were detected at 0° to the beam direction, thereby preferentially selecting $L=0\mathrm{}$ transfers of neutron-proton pairs. A Ge(Li) detector at 90° detected the $\gamma$ rays with good energy resolution. Angular distributions for the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}({}_{}{}^3{}_{}{}^{}\mathrm{He},p){}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ reaction were measured with a magnetic spectrograph. These, together with previous results on the ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}({}_{}{}^3{}_{}{}^{}\mathrm{He},p){}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$ reaction, gave precise information on the intensities of the states excited, as well as their energies. The main purpose of the experiments was to measure the $\gamma$ decay of the lowest-lying isobaric analog states in ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$. The analog state in ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ was found to decay primarily (85%) to the 842-keV level and secondarily (15%) to the ground state. The analog state in ${}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$ decays in a more complex fashion to several states. The strongest transition (55%) is to the 4091-keV state. $\gamma$-ray decay schemes for several other low-lying even-parity levels in ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$ were also measured. The observation that the 4091-keV level of ${}_{}{}^{41}{}_{}{}^{}\mathrm{Ca}$ decays (34%) to the ${\frac{7}{2}}^{-}$ ground state and (58%) to the ${\frac{3}{2}}^{+}$ level at 2009 keV suggests a ${\frac{5}{2}}^{+}$ assignment. The implications of the measurements are discussed, particularly with reference to the structure of low-lying two-particle-one-hole states in these nuclei.