Energy Dependence in (He3,t) Transitions to Isobaric Analog Ground States

Abstract

Transitions to the isobaric analog ground states of ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{62}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ have been studied with the (${}_{}{}^3{}_{}{}^{}\mathrm{He},t$) reaction in the energy range of 21.4 to 37.5 MeV. Large variations in the shape of the experimental angular distributions were observed as a function of energy and target nucleus. These effects were poorly described by distorted-wave Born-approximation calculations based on a simplified shell-model theory. Calculations based on a generalized optical model, using different interaction terms for each nucleus, gave a somewhat better description. Interaction strengths, normalized to fit the data, required a significant decrease with increasing energy for both theoretical models. These effects were general, to a large extent independent of the optical-model parameter set used. The poor description, both in shape and in strength, of the energy dependence of the data is evidence of basic inadequacies in the theories as they are presently used.