Exchange interpretation of the large-angle scattering of alpha particles from nuclei

The anomalous large-angle scattering of medium-energy α particles is interpreted in terms of an exchange process. An exchange amplitude ("knock on"), calculated in the distorted-wave Born approximation, is evaluated paying particular attention to the antisymmetrization of the A+4 nucleon system. This amplitude is combined with a scattering matrix appropriate to fit just forward-angle elastic scattering. It is shown that only the highest possible orbital angular momentum cluster (L=8 for ⁴⁰Ca) is significant and leads to agreement with experiment. This agreement is achieved with only one adjustable parameter, the spectroscopic factor, which turns out to be quite small. It is shown that this microscopic caluclation may provide a basis for the phenomenological Regge pole description of this process.