Effects of nuclear orientation on fusion and fission process in heavy ion reactions

Nishio, Katsuhisa   ; Ikezoe, Hiroshi; Mitsuoka, Shinichi; Nishinaka, Ichiro; Watanabe, Yutaka*; Nagame, Yuichiro ; Otsuki, Tsutomu*; Hirose, Kentaro*; Hofmann, S.*

Effects of nuclear deformation of U on fusion and fission was investigated in the reactions of Si+U and S + U. From the measurement of evaporation residue cross-sections for Si+U, carried out at GSI, it is concluded that in the sub-barrier region competition between fusion and quasi-fission was suggested whereas at the above barrier region fusion is the main process after the system is captured inside the Coulomb barrier. The fission fragment mass distributions were measured in Si+U and S+U at the JAEA tandem facility. Symmetric fission was observed at the above-barrier region, showing the fusion-fission character. In decreasing the energy to the sub-barrier, the asymmetric fission starts to dominate, showing the signature of quasi-fission. The results suggest that the equatorial collision results in fusion whereas the polar collision results in quasi-fission.