The relationship between the threshold energy for a deep sub-barrier fusion
hindrance phenomenon and the energy at which the regime of interaction changes
(the turning-off of the nuclear forces and friction) in the sub-barrier capture
process, is studied within the quantum diffusion approach. The quasielastic
barrier distribution is shown to be a useful tool to clarify whether the slope
of capture cross section changes at sub-barrier energies.Comment: 4 pages, 4 figures (accepted in Eur. Phys. J. A
