Fusion of Ca-48+Zr-90,Zr-96 above and below the Coulomb barrier

Fusion-evaporation cross sections were measured in the two systems 48Ca+90,96Zr in an energy range from well below to well above the Coulomb barrier. The sub-barrier fusion of 48Ca+90Zr is reproduced by coupled-channels calculations including the lowest quadrupole and octupole vibrations of 90Zr, and using a Woods-Saxon potential with a standard diffuseness parameter a = 0.68 fm. However, the fusion cross sections are overestimated above the barrier. The low-energy slope of the excitation function for 48Ca+96Zr is steeper. This implies a larger diffuseness parameter a = 0.85 fm. Fusion cross sections are well fit in the whole energy range, and the effect of the strong octupole vibration in 96Zr is predominant. The extracted fusion barrier distributions are reasonably well reproduced by calculations for both systems. A comparison with previous data for 40Ca+90,96Zr is made in an attempt to clarify the role of transfer couplings in sub-barrier fusion.