A simple approach to $\alpha$-decay fine structure
  We propose a simple method to evaluate $\alpha$-transition rates to low-lying excited states in even-even nuclei. For this a realistic $\alpha$-daughter double folding interaction is approximated by a parabola in the region where the decay process takes place. This allows us to evaluate the penetration probability analytically. The main experimental features of branching ratios to excited states are reproduced by this simple approach. 
D.S. Delion, Monika Patial, R.J. Liotta, and R. Wyss
nucl-th