Distorted-Waves Theory of Double-Excitation by Inelastic Scattering

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Abstract
It is shown how the distorted-waves theory of inelastic scattering can give rise to angular distributions with "anomalous phase," such as observed in recent experiments with alpha particles. These occur when the scattering takes place through second-order effects; excitation of a two-phonon vibrational state is studied explicitly. There is an important cancellation between the amplitude for simultaneous excitation and part of that for successive excitation, without which the anomalous phase would not be observed. These conclusions are contrasted with the predictions of a theory using plane-wave Born approximation. Further study of the cancellation is suggested as a sensitive test of the optical model.