(p,n) Reactions onSr88andY89and the Reaction Mechanism via Isobaric Spin-Analogue Resonances

Differential cross sections for the reactions ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}\mathrm{}(p,n)\mathrm{}{}_{}{}^{88}{}_{}{}^{}\mathrm{Y}$ (ground state), ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}\mathrm{}(p,n)\mathrm{}{}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}$ (ground state), and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}\mathrm{}(p,n)\mathrm{}{}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}_{}^{*}{}_{}{}^{}$ (590-keV state) are investigated in the vicinity ($E_p\approx 5$ MeV) of $d_{\frac{5}{2}}$ isobaric analogue states in the compound nuclei ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. Angular distributions and forward angle excitation functions of the neutrons from these reactions are investigated by a time-of-flight method in conjunction with a pulsed proton beam. The observed energy dependence and the angular dependence of the neutrons are analyzed in terms of mixing of the isobaric analogue state with the background states of the compound nucleus. The experimental results can be explained by the two-channel $R$-matrix theory of the isobaric analogue resonance and the statistical compound-nuclear reaction theory.