Nuclear Data Sheets for A = 208

Surface α-clustering and α-decays of 212Po

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 angular distributions, displaying an anomalous large angle enhancement, yielded unique optical potentials, whose real part is determined with good accuracy up to small internucleus distances, and we investigate their properties; we then analyze the general compatibility of these potentials with the microscopic requirements resulting from the constraints due to antisymmetrization, in the case of a system which was thoroughly investigated from a microscopic point of view, and whose spectroscopy is well agreed upon, that is, the 20Ne = α + 16O system. The local potential approach is then applied to the 44Ti = α + 40Ca system - which is the analogue of 20Ne in the fp-shell -whose α-cluster spectroscopy remained unclear for a long time and for which microscopic calculations led to contradictory interpretations; not only does this simple model give a nice account of the energy location and intraband electromagnetic transition probabilities for the members of the 44Ti ground state band, but it predicts the existence of excited alpha-cluster bands, which were subsequently identified experimentally in alpha-transfer experiments. The same approach is applied to the 40Ca = α + 36Ar system, where similar predictions have recently been confirmed experimentally, and to other systems close to the sd-shell closure region. Finally the persistence of alpha-cluster structure in medium-weight and heavy nuclei is discussed within the local potential approach.

Local Potential Approach to the Alpha-Nucleus Interaction and Alpha-Cluster Structure in Nuclei

The preformation factors of alpha clusters for fully-favoured alpha decay of even–even heavy nuclei, 82 < Z <114, 126 < N <170, were determined using the alpha preformation formula taken from the hypothesized cluster-formation model of our previous work. In this model, the formation of an alpha particle inside the parent nuclei was considered as a quantum-mechanical cluster-formation state. The eigenvalues of these states are determined from the differences between the binding energies. The total energy of the considered total system state was investigated by adopting the alpha-decay energy and the energy of the open-shell nucleons. The clustering amount was also calculated on the basis of this model. The results showed a very good consistency with the alpha-decay constants. This model presents a significant step forward in the determination of realistic preformation factors.

https://iopscience.iop.org/article/10.1088/0954-3899/40/6/065105/pdf

R. M. Devries

Papers

A comparison of α-transfer and α-decay in the lead region

Inverse α Decay via the Reaction 208 Pb( 16 O, 12 C) 212 Po