(32) S + ~ (90,96) Zr Quasi-projectile Scattering To Extract The Barrier Distribution And The Study Of Neutron Transfer Effect

Neutron transfer channels of which transfer Q values are positive make the barrier distribution flat and almost structureless and extend to very low energies. The barrier distribution enhances the sub-barrier fusion cross sections strongly. Some experiments have found that the large enhancement could not be explained without the considering of neutron transfer, but proton transfer has only a minor effect. Transfer-channel couplings are completely different from other couplings of the intrinsic degrees of nucleus. There are different points of view about the nucleon transfer coupling mechanism now. Accounting for this mechanism will help to set up the foundation of the unified coupling model in theory.We selected the ~32S +~90,96Zr as the investigated systems. The main difference between those two reactions is in the neutron transfer Q values which are positive, in the case of ~96Zr only, up to the pickup of six neutrons. So the two reactions are appropriate for the investigation of transfer-channel couplings.The experiment were performed at HI-13 tandem Van-de Graff accelerator of China Institute of Atomic Energy, Beijing. Quasi -elastic cross sections have been measured for ~32S + ~90,96Zr with high accuracy near the coulomb barrier at seven backward angles. The extracted barrier distributions D~qel(E) have different shapes, with a wider and flat structure for ~32S + ~96Zr, so the low-energy fusion cross sections have a large enhancement compared to ~32S + ~90Zr.In theory, the coupling channel equations have been used to describe the near and sub-barrier heavy-ion fusion reactions. The couplings between the entrance channel and the other channels have appreciable effects on sub-barrier fusion cross section. Instead of single fusion barrier, these couplings lead to a distribution of fusion barrier D~fus(E). The barrier distributions, D~fus(E) and D~qel(E), have been derived from fusion excitation function and quasi-elastic scattering excitation function. The ECIS and CCDEF codes have been used to calculate the quasi-elastic cross sections and fusion cross sections near the coulomb barrier respectively. Barrierdistributions are extracted for the comparison with the result from experiment. At the end, further investigation is looked forward.