Excitation of Two-Phonon States by Inelasticα-Particle Scattering

Recent experiments on inelastic scattering of 40-MeV $\alpha$ particles have shown that the angular distributions from the excitation of some known $4^{+}$ states in medium weight nuclei are not in accord with the Blair phase rule. Calculations are reported which indicate that the anomaly arises as an interference effect between two possible mechanisms for exciting the first $4^{+}$ state, i.e., a direct transition and a multiple transition. This conclusion is contrary to previous interpretations based on plane-wave perturbation calculations. It is suggested that experiments of this type, and the analysis given here, promise to be a useful tool for the study of higher excited states.