Evidence for hindrance in fusion between sulfur and lead nuclei

The influence of the structure of projectile and target nuclei on the capture cross sections was investigated for the reactions S-34 + Pb-204,Pb-206,Pb-208 and S-36 + Pb-204,Pb-206,Pb-208. Capture cross sections were deduced by measuring the fission fragments using multiwire proportional counters. An enhancement of the capture cross sections relative to a one-dimensional barrier penetration model was observed for all reactions at energies below the interaction barriers. The enhancement is larger in the case of reactions with S-34 than with S-36. This observation is explained by a stronger coupling to the vibrational states in the reactions with S-34. Comparing the capture cross sections and the evaporation-residue cross sections for the reactions S-36 + Pb-206 and S-34 + Pb-208, both yielding the same compound nucleus Cf-242, it is shown that the latter reaction has a lower fusion probability.