Interplay of Neutron Transfer in the Fusion Process of 16 O + 112,116,120 Sn and 18 O + 116 Sn Systems at Sub-barrier Energies

In a sub-barrier energy region, the fusion mechanism of 16 O + 112,116,120 Sn and 18 O + 116 Sn reactions has been theoretically examined by using the one-dimensional Wong formula, the symmetric-asymmetric Gaussian barrier distribution (SAGBD) model, and the coupled channel formalism. For the abovementioned systems, predictions of the one-dimensional Wong formula remain substantially smaller than the sub-barrier fusion data. To address the fusion data, coupled channel calculations have been performed by using the code CCFULL. In the coupled channel calculations, the main effects of intrinsic degrees of freedom associated with the structure of the fusing pairs have been considered. For the 16 O + 112,116,120 Sn systems, the fusion enhancement can be traced back to couplings to inelastic excitations of 2^ + and 3^ - vibrational states. However, for the 18 O + 116 Sn reaction, the sub-barrier fusion enhancements cannot be explained by couplings to vibrational degrees of freedom alone. In this case, couplings to two neutron (2n) transfer channels with positive Q -value are needed to reproduce the observed fusion enhancement. On the other hand, the SAGBD calculations remove the discrepancies between the cross section of the one-dimensional Wong formula and the experimental results reasonably. Thus, the SAGBD-based results remarkably explain the fusion data of the studied reactions. In the SAGBD model, the large and non-zero values of λ and V_CBRED for the chosen systems indicate that the nuclear structure of the fusing partners plays a very crucial role in the fusion dynamics of 16 O + 112,116,120 Sn reactions while positive Q - value neutron transfer channels and inelastic surface excitations of the collision partners collectively produce a more pronounced effect on the fusion of 18 O + 116 Sn reaction at sub-barrier energies.