Systematics of the proton stripping reaction onGa69,71,As75,Br79,81isotopes and nuclear structure of the Ge-Se isotopes

Abstract

The ${}_{}{}^{69}{}_{}{}^{}\mathrm{Ga}({}_{}{}^3{}_{}{}^{}\mathrm{He}, d){}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$ and ${}_{}{}^{75}{}_{}{}^{}\mathrm{As}({}_{}{}^3{}_{}{}^{}\mathrm{He}, d){}_{}{}^{76}{}_{}{}^{}\mathrm{Se}$ reactions have been studied at 25 MeV incident energy using a split-pole spectrometer. The over-all resolution is 18-21 keV. Sixty-two ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$ levels, 16 of which observed for the first time, are populated below 5.2 MeV excitation energy. Seventy-one ${}_{}{}^{76}{}_{}{}^{}\mathrm{Se}$ levels are separated, 44 of which had never been observed. Angular distributions are obtained and comparison with distorted-wave-Born-approximation calculations allows parity assignment and spin limits for many levels. Spectroscopic factors are deduced for most of the observed transitions. In order to test our mixing of orbital momenta, the ${}_{}{}^{69}{}_{}{}^{}\mathrm{Ga}(\alpha , t){}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$ reaction has also been performed at 39.35 MeV incident energy. A cursory investigation of the ${}_{}{}^{79,81}{}_{}{}^{}\mathrm{Br}({}_{}{}^3{}_{}{}^{}\mathrm{He}, d)$ reactions has been performed and systematics are drawn for the first excited levels between $N=38\mathrm{} \mathrm{and} 46$. The model previously presented to account for the strong population of the ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}$ $0_2^{+}$ level in our earlier study of ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}$ with the same reaction is discussed and compared with the present results. From present and previously known experimental systematics, conclusions are drawn concerning the possibility of an oblate to prolate shape transition between $N=36\mathrm{} \mathrm{and} 46$, the softness of the nuclei in the $N=40\mathrm{}$ region, and the noncollective structure of the $0_2^{+}$ state. Potential energy surfaces obtained by Hartree-Fock calculations using the Skyrme interaction are presented and confirm the above conclusions.