Heavy-ion fusion reactions near the coulomb barrier for medium-heavy systems

Medium-heavy systems give the opportunity of studying in detail the effects of channel couplings on near- and sub-barrier fusion. The cases of Ca-40,Ca-48 + Zr-90,Zr-96, and Ca-40 + Zr-94 are particularly attractive from several points of view. Various physical issues concerning the nuclear potential, inelastic and, possibly, transfer couplings are put in evidence and discussed, by comparing the measured excitation functions and the extracted fusion barrier distributions with the results of coupled-channels calculations. A systematic comparison of the experimental data for the five systems is also done. It is pointed out that measurements of fusion cross sections at very low energies for the Ca+Zr systems, would extend our knowledge on the recent evidences of fusion hindrance in the far sub-barrier energy regime.