(p, n) Isobaric Analog Transitions in Targets ofAl27,V51, andZr90at 22, 30, and 40 MeV

Angular distributions for ($p, n$) transitions to isobaric analog states of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$, and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ targets have been measured at proton energies of 22, 30, and 40 MeV. The data have been compared with results of macroscopic distorted-wave Born-approximation calculations employing various form factors: pure volume, pure surface, and mixtures of real volume with imaginary surface. The comparisons show that: (i) The surface interaction describes the data rather well, particularly at the lower energies, whereas the volume interaction is adequate only at 40 MeV; (ii) complex mixtures of volume and surface give good descriptions of most of the data if the mixture is a variation of the isospin part of the Becchetti-Greenless potential with either increased surface-to-volume ratio or increased imaginary radius; (iii) use of the unmodified Becchetti-Greenless geometry gives a poor fit to much of the data; (iv) the strength of the isospin interaction decreases with increasing energy, in general agreement with other charge-exchange work. Most of the decrease here occurs between 22 and 30 MeV. This is true for the surface interaction and for each of the two complex interactions.