Coupled channels description of the α-decay fine structure

We review the coupled channels approach of alpha transitions to excited states. The alpha-decaying states are identified as narrow outgoing Gamow resonances in an alpha-daughter potential. The real part of the eigenvalue corresponds to the Q-value, while the imaginary part determines the half of the total alpha-decay width. We first review the calculations describing transitions to rotational states treated by the rigid rotator model, in even-even, odd-mass and odd-odd nuclei. It is found that the semiclassical method overestimates the branching ratios to excited 4(+) for some even-even alpha-emitters and fails in explaining the unexpected inversion of branching ratios of some odd-mass nuclei, while the coupled-channels results show good agreement with the experimental data. Then, we review the coupled channels method for alpha-transitions to 2(+) vibrational and transitional states. We present the results of the Coherent State Model that describes in a unified way the spectra of vibrational, transitional and rotational nuclei. We evidence general features of the alpha-decay fine structure, namely the linear dependence between alpha-intensities and excitation energy, the linear correlation between the strength of the alpha-core interaction and spectroscopic factor, and the inverse correlation between the nuclear collectivity, given by electromagnetic transitions, and alpha-clustering.