Heavy-ion fusion reaction mechanism for superheavy element synthesis

We have investigated the reaction mechanism of heavy-ion fusion at energies around the Coulomb barrier in order to find a new possibility to synthesize the superheavy element with larger production cross sections. One possibility is hugging fusion of well-deformed nuclei, and another is to use shell-closed nuclei as colliding partner. We found that the fusion probability strongly depends on the orientation of the nuclear deformation. When the projectile collides at the tip of the deformed nuclei, large fusion hindrance was observed, whereas in the side collision the complete fusion occurs without any hindrance. This supported the theoretical idea of hugging fusion that the compact touching configuration in the side collision is more favorable for complete fusion than the elongated configuration in the tip collision. We also investigated the dependence of the fusion probability on the nuclear structure of colliding partner. No fusion hindrance was observed in the reactions of neutron shell closure even in massive system. Recently we started to measure large-angle quasi-elastic scattering in order to extract experimentally the barrier distribution for the superheavy element synthesis. (author)