Alpha-Resonances in Medium and Heavy Nuclei I. Review of Microscopic Models

We review microscopic approaches describing α-like resonances in nuclei with Z ≥ 50. We give a microscopic explanation of α-like rotational bands in the 40Ca+α system in terms of single particle Gamow resonances. On the other hand, we show that for α-decaying nuclei the decay width can be described only in terms of a preformed α-cluster, existing on the nuclear surface in addition to the standard mean field cluster. Thus, we use a semi-microscopic hybrid model combining the mean field formation with a preformed α-cluster in order to explain the order of magnitude of the experimental decay width. Finally, we analyze proton-neutron versus α-like correlations.