Dynamics of complete and incomplete fusion of 6,7Li, 15N and 16O with a 209Bi target

Abstract

The dynamics of complete and incomplete fusion of 6,7Li, 15N and 16O with a common target (209Bi) around the Coulomb barrier are analyzed within the context of the coupled channel formulation and the energy dependent Woods-Saxon potential (EDWSP) model. The calculated results are compared with experimental fusion cross-sections and it has been shown that complete fusion (CF) data of weakly bound projectile with a heavy target (209Bi) gets suppressed at above barrier energies. In the case of the 6Li + 209Bi (7Li + 209Bi) reaction, the CF data at above barrier energies is reduced by 34% (26%) with reference to the expectations of the coupled channel approach. However, the theoretical estimations due to the EDWSP model can minimize the suppression factor by 9% with respect to the reported value and consequently the portion of above barrier CF cross-section data of 6Li + 209Bi (7Li + 209Bi) reaction is suppressed by 25% (17%) when compared with the present model calculations. This fusion inhibition can be correlated with the low breakup threshold of projectile which in turn breaks up into two fragments in the entrance channel prior to fusion barrier. The total fusion (TF) data, which is sum of complete fusion (CF) data and incomplete fusion (ICF) data, is not suppressed when compared with the predictions of the theoretical approaches and thus breakup channel has very little influence on the total fusion cross-sections. Although the breakup fragments appeared in both reactions, the enhanced suppression effects observed for the lighter projectile can be correlated with its low binding energy associated with the $\alpha$ -breakup channel. Further the outcomes of the EDWSP model reasonably explained the ICF contribution appeared in the fusion of 6,7Li + 209Bi reactions. In contrast to this, the observed fusion dynamics of 15N + 209Bi and 16O + 209Bi reactions, wherein the collective excitations such as two phonon, three phonon vibrational states contribute to produce below barrier fusion enhancement, has been adequately explored by the adopted models, and henceforth ensures the stability of well bound nuclei against breakup effects.