Local potential approach to the alpha-nucleus interaction and alpha-cluster structure in nuclei

We review the merits of the local potential approach in the description of elastic alpha-particle scattering and of alpha-cluster structure in medium- weight nuclei. We recall how optical model analyses of elastic scattering a ngular distributions, displaying an anomalous large angle enhancement, yiel ded unique optical potentials, whose real part is determined with good accu racy up to small internucleus distances, and we investigate their propertie s; we then analyze the general compatibility of these potentials with the m icroscopic requirements resulting from the constraints due to antisymmetriz ation, in the case of a system which was thoroughly investigated from a mic roscopic point of view, and whose spectroscopy is well agreed upon, that is , the Ne-20 = alpha + O-16 system. The local potential approach is then app lied to the Ti-44 = alpha + Ca-40 system - which is the analogue of Ne-20 i n the fp-shell - whose alpha-cluster spectroscopy remained unclear for a lo ng time and for which microscopic calculations led to contradictory interpr etations; not only does this simple model give a nice account of the energy location and intraband electromagnetic transition probabilities for the me mbers of the Ti-44 ground state band, but it predicts the existence of exci ted alpha-cluster bands, which were subsequently identified experimentally in alpha-transfer experiments. The same approach is applied to the Ca-40 = alpha + Ar-36 system, where similar predictions have recently been confirme d experimentally, and to other systems close to the sd-shell closure. regio n. Finally the persistence of alpha-cluster structure in medium-weight and heavy nuclei is discussed within the local potential approach.