Fusion of Ca-40+Sn-124 at subbarrier energies

Fusion-evaporation cross-sections of Ca-40 + Sn-124 have been measured, fol lowing a recent experiment on multinucleon transfer processes in the same s ystem. The Ca-40 XTU Tandem beam was used (similar to 5 pnA), and the evapo ration residues were detected at 0 degrees and at small angles by an Energy -TOF telescope following an electrostatic beam deflector. High statistical accuracy was achieved (similar to 1% near the barrier). A few energy points were measured for Ca-40 + Sn-116, too. The two fusion excitation functions are similar to each other and are greatly enhanced at low energies over th e simple one-dimensional barrier penetration estimate. The fusion barrier d istribution of Ca-40 + Sn-124 was extracted from the data as the second der ivative of E x sigma with respect to the energy. Its shape is wide without separated peaks, similar to the recent result for Ca-40 + Zr-96; where it w as attributed to a dominant effect of couplings to neutron transfer channel s with positive Q-values. Such channels are available in Ca-40 + Sn-124 as well and they are known to be very strong from the multinucleon transfer ex periment. Simplified coupled-channel calculations including surface vibrati ons and sequential neutron pick-up channels are unable to account for the d ata. The peculiar Pole of the strong. 3(-) octupole vibration of Zr-96 is p ointed out.