Suppression of complete fusion in theLi6+Sm144reaction

Abstract

Complete fusion excitation function for the $^{6}\mathrm{Li}+^{144}\mathrm{Sm}$ reaction has been measured at near barrier energies by the activation technique. Coupled-channel calculations show an enhancement in fusion cross section at energies below the barrier compared to the one-dimensional barrier penetration model calculation, but they overpredict it in the entire energy range compared to the experimental data. Reduced fusion cross sections for the present system at energies normalized to the Coulomb barrier were also found to be systematically lower than those with strongly bound projectiles forming a similar compound nucleus. These two observations conclusively show that the complete fusion cross section, at above barrier energies, is suppressed by $~32%$ in the $^{6}\mathrm{Li}+^{144}\mathrm{Sm}$ reaction. Reanalyses of existing fusion data for $^{7}\mathrm{Li}+^{165}\mathrm{Ho}$ and $^{7}\mathrm{Li}+^{159}\mathrm{Tb}$ also show a suppression compared to those with strongly bound projectiles, which contradicts earlier conclusions. The fusion suppression factor seems to exhibit a systematic behavior with respect to the breakup threshold of the projectile and the atomic number of the target nucleus.