Effect of nuclear shell structure on fusion reaction

The dependence of the fusion reaction on the nuclear shell structure was investigated for the two reaction systems 82Se + 138Ba and 82Se + 134Ba, where the nucleus 138Ba has a closed neutron shell N = 82, while the nucleus 134Ba has a neutron number 78. Evaporation residues for these fusion reactions were measured near the Coulomb barrier region. The measured evaporation residue cross sections for the reaction system 82Se + 138Ba were two orders of magnitude larger than those for the reaction system 82Se + 134Ba in the excitation energy region of 20-30 MeV. The evaporation residue cross sections were compared with those of the other reaction systems that produce the same compound nucleus as the present systems. It was found that the fusion reaction 82Se + 138Ba occurs without hindrance, while that of 82Se + 134Ba is considerably hindered, as commonly observed in the massive reaction system with the charge product ZpZt > 1800 of projectile and target. This suggests the importance of the shell closure N 82 in the heavy-ion fusion reaction