Systematic study of elastic scattering and fusion induced by weakly bound 6Li on medium mass targets. Threshold anomalies

Abstract

Using the extended optical model, a comparative and systematic analysis of different 6Li-induced reactions at sub- and above-barrier energies is carried out. Collisions with 58Ni, 59Co, 64Ni and 64Zn are analyzed. For each selected system, the São Paulo potential is used as a bare potential, a surface polarization potential is added to simulate the effects of direct reactions and a volume potential is considered to account for couplings to fusion. Simultaneous fits to the corresponding elastic scattering and fusion data of each system are optimized at the different energies measured, and the validity of the respective dispersion relations is verified. Based on the potentials obtained for each selected system, the elastic scattering data are properly described and the fusion cross sections are well reproduced at the energies around and above the barrier. For the 6Li + (58Ni, 64Zn) systems, some abnormal strength values are found for the fusion polarization potentials at sub-barrier energies, which would invalidate the dispersion relation. A possible explanation is put forward and, as a result, it is concluded that the constriction of dispersive potentials might help identify unphysical data. For all systems, the final energy dependence of the surface polarization potential is found to be consistent with the Breakup Threshold Anomaly, while the fusion polarization potential follows the Threshold Anomaly.