Study of transfer channel coupling and entrance channel effects for the near and sub-barrier fusion of , and systems

The fusion excitation functions for the 46 Ti+ 64 Ni , 50 Ti+ 60 Ni and 19 F+ 93 Nb systems have been measured from ∼ 10% below to 15% above the nominal Coulomb barrier, utilizing the recoil mass separator, HIRA at the Nuclear Science Centre, New Delhi. Mean spins have been deduced from the fusion cross sections by two different methods, one using the statistical model and the second by a fit to the fusion cross sections. Good agreement is found between them. It is seen that the simplified coupled-channel calculations, with couplings to the lowest surface inelastic excitations alone, do not explain both the observed fusion cross sections and mean spins in the low energy domain for all the three systems. A systematic comparison is made between the systems 46 Ti+ 64 Ni and 50 Ti+ 60 Ni which have quite different ground-state transfer Q -values ( Q gg ) for the transfer channels. The 46 Ti+ 64 Ni system shows a significant enhancement of the sub-barrier fusion cross section and mean spin as compared with the 50 Ti+ 60 Ni system, indicating the importance of the transfer channel coupling. Fusion cross section and mean spin have been studied for the near and sub-barrier fusion of the highly mass asymmetric system 19 F+ 93 Nb and compared with those for the 48 Ti+ 64 Ni system leading to the same compound nucleus via the nearly symmetric entrance channel. Since the 19 F+ 93 Nb system has a large positive Q gg for one-proton pick-up, the fusion data have been complemented by one-nucleon transfer measurements at energies around the Coulomb barrier. A simultaneous analysis of the fusion excitation functions and mean spin data indicates no significant effects that may be related to the entrance channel mass asymmetry.