Investigation of the role of neutron transfer and fusion hindrance in ²⁸Si+¹⁵⁸Gd at deep sub-barrier energies

The challenging task in heavy-ion collisions is unambiguously identifying the true fusion events in the deep sub-barrier region. Considering the primary challenge, we have measured fusion excitation functions for Si-28+ Gd-158 reaction at energies above to deep sub-barrier region to decipher the role of multineutron transfer with positive Q value and fusion hindrance in an asymmetric system. A comparison has been made with our previous measurement for Si-30+ Gd-156 system where only one transfer channel with Q > 0 exists and populates the same compound nucleus Pt-186 *. The enhancement in fusion cross sections is observed on a reduced scale in the Si-28+ Gd-158 reaction over Si-30+ Gd-156 system at sub-barrier energies. The measured fusion data and extracted barrier distribution have been analyzed within the framework of coupled-channels (CC) programs, CCFULL and empirical channel coupling. Coupling to rotational excitations in projectile and target along with up to 2n transfer channel with positive Q value is found to be promising to explain the fusion excitation functions except for the lowest energy point. However, the influence of more than two neutrons transfer is insignificant in Si-28+ Gd-158 system. At the lowest energy (approximate to 14% down the Coulomb barrier), a deviation from standard CC has been found, which may indicate the threshold for fusion hindrance, but additional lower-energy data are needed to prove this. The experimental threshold energy (E-S) for fusion hindrance is in good agreement with the empirical formula, and it is consistent with the observed pattern of E-S as a function of the entrance channel parameter (zeta) for other nearly symmetric and asymmetric systems.