Sub-barrier fusion of 34,36S+204,206,208Pb: Signature of isotopic dependence of repulsive core potential in heavy-ion fusion reactions

Abstract

The measurements of the excitation function for the heavy-ion fusion-fission cross sections in negative Q-value systems 34S+204,206,208Pb and 36S+204,206,208Pb have been analyzed by coupled-channels (CC) calculations based on the M3Y double-folding (DF) potential that is supplemented with a short-ranged repulsive potential. The standard Aage Winther potential is also employed to explore the occurrence of the unexpected steep fall-off phenomenon of the measured cross sections in fusion between sulfur and lead nuclei. Our analysis based on the deep phenomenological potentials clearly demonstrates that the fusion data are strongly hindered at incident energies well below the Coulomb barrier for the four heavy-ion systems 34S+206Pb, 34S+208Pb, 36S+206Pb and 36S+208Pb. In addition, a first indication of a maximum in the trend of the experimental data of the S-factor representation has been observed for each of the fusions of 34,36S with 206,208Pb targets. It is shown that the M3Y+Repulsion potential accompanied by the CC calculations provides a satisfactory description of the experimental fusion cross sections and S factors in the whole energy range under study for all the six cases of interest. A discussion is also presented concerning the isotopic dependence of the parameters existing in simulation of the repulsive core potential. Our detailed study reveals that the strength of the repulsive interaction and incompressibility of the nuclear matter (NM) increases and decrease linearly with addition of neutrons in the isotopic systems, respectively. Further, we show that the repulsive part of the density distribution becomes more diffuse with increasing neutrons from 34S+204Pb to 36S+208Pb.