Differential cross sections have been measured for the (p,n) reaction to the isobaric analog states of ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$, and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ at an incident energy of 27 MeV. Because of the importance of collective effects in this mass region, coupled-channel calculations have been carried out in the analysis of the data. Optical potentials obtained from the Lane model for the charge exchange reaction have been used in the simultaneous analysis of coupled proton and neutron channels. The sensitivity of the calculations to the different couplings between the levels and to the magnitude of the isovector potentials, $V_1$ and $W_1$, is discussed. The good agreement obtained between the measured and calculated (p,n) angular distributions to the analog state confirms the validity of the Lane formalism for high-$Z$ nuclei ($Z\ge 50$). Elastic neutron differential cross sections inferred from the coupled-channel analysis are compared with measurements available in the literature in the energy range 7-8 MeV. The results of these calculations agree with the measured values as well as the results of calculations made using global neutron optical potential parameters optimized to fit neutron data.

NUCLEAR REACTIONS ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$, ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$(p,n)IAS; $E=27\mathrm{}$ MeV; Measured $\sigma \left(\theta \right)$ for ground-state analog transition; deduced (n,n)$\sigma \left(\theta \right)$, $E=7-8\mathrm{}$ MeV; coupled-channel analysis.

• Received 14 January 1983

DOI:https://doi.org/10.1103/PhysRevC.28.1934