Density variation effects in α + 208pb and 16O + 208Pb fusion reactions

We propose a hybrid approach between the sudden model and the adiabatic model to explain the fusion hindrance in heavy-ion fusion reactions at deep subbarrier energies. Due to the strong Pauli blocking effects at the density overlap region, the a particle approaching the target Pb-208 becomes enlarged and its density distribution gets changed. By introducing energy dependence into this density variation effect, the potentials at different colliding energies are diverse. With the decrease of colliding energies, the significantly enhanced density variation effects make the nuclear potential more attractive and result in a deeper pocket in the inner part. A reasonable description of the experimental fusion cross sections is achieved for the alpha + Pb-208 reaction. On account of highlighting the influence of density variation effects on the fusion process at deep subbarrier energies, we further investigate the density variation effects in the O-16 + Pb-208 fusion reaction based on the a-cluster structures in O-16 nuclei. The fusion hindrance at deep subbarrier energies is described well by considering the density variation effects. In addition, an astrophysical S factor between the sudden model and adiabatic model is predicted at the energies below the experimental data.