The differential analyzing power, $A\left(\theta \right)$, was measured in the quasielastic ($p,n$) reaction on ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$. The energy of the incident polarized proton beam was 24.5 MeV except in the case of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ where it was 20.3 MeV. The $A\left(\theta \right)\text{'}\mathrm{s}$ were oscillatory with a large forward-angle maximum of ± (0.25 to 0.35). Distorted-wave Born-approximation calculations using a macroscopic model give reasonable agreement with the data for ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$. ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$. For the Sn isotopes, good agreement is found when an isospin-dependent spin-orbit term is added to the form factor. The sign of this term agrees with that given by a simple model, but its magnitude is poorly determined due to optical-model ambiguities.

• Received 19 May 1972

DOI:https://doi.org/10.1103/PhysRevC.6.1698