Systematics of the αα-decay fine structure in even–even nuclei

We describe αα-transitions to low-lying states in even–even nuclei with Z>50,N>82 using the Coherent State Model (CSM). We reproduce the energy levels and electromagnetic transition rates between the states of the ground band employing two parameters, namely the deformation parameter and the strength of the harmonic CSM Hamiltonian. The B(E2) values are described in terms of an effective charge which depends linearly on the deformation parameter. The treatment of the αα-emission process is based on an αα–daughter interaction containing a monopole component, calculated through a double folding procedure with a M3Y interaction plus a repulsive core simulating the Pauli principle, and a quadrupole–quadrupole (QQ) interaction. The decaying states are identified with the lowest narrow outgoing resonances obtained through the coupled channels method. The αα-branching ratios to 2+2+ states are reproduced by means of the QQ strength. This interaction strength can be fitted with a linear dependence on the deformation parameter, as predicted by the CSM. The theoretical intensities to 4+4+ and 6+6+ states are in reasonable agreement with available experimental data. Predictions are made for spherical, transitional and well deformed even–even αα-emitters.