Proton Spin Flip in the ReactionC12(p,p′)C*12[4.44 MeV]

Abstract

The angular correlation between protons inelastically scattered from the first excited state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and the subsequent 4.44-MeV deexcitation $\gamma$ radiation perpendicular to the scattering plane was measured for 26.2- and 40.0-MeV incident proton energy. This correlation has previously been shown to be related to the fraction of protons undergoing spin flip along this direction. As has been observed at lower bombarding energies, the spin-flip probability peaks at large proton scattering angles; observed here are probabilities as high as 0.35 near 150°. The spin-flip probability for all inelastic scattering to the 4.44-MeV state is 3%. The data were compared to the predictions of the distorted-wave Born approximation, using collective-model and microscopic-model form factors. The expected sensitivity to the spin-dependent part of the nucleon-nucleus interaction was confirmed. However, it was found that the observed spin flip was almost entirely accounted for by distortions in the entrance and exit elastic channels, due to the spin-orbit term in the optical-model potential. No definite conclusions regarding the spin-dependent part of the inelastic interaction could be reached from the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ data, possibly owing to the failure of the assumptions of the optical model for such light nuclei. It appears that meaningful information regarding the spin dependence of the reaction mechanism producing the excited state can be obtained from spin-flip data only for those nuclei having well-determined optical-model parameters.