Heavy-ion fusion and fission study at JAEA

Hirose, Kentaro  ; Nishio, Katsuhisa   ; Ikezoe, Hiroshi; Mitsuoka, Shinichi; Nishinaka, Ichiro; Makii, Hiroyuki   ; Wakabayashi, Yasuo*; Tsukada, Kazuaki  ; Asai, Masato  ; Nagame, Yuichiro ; Kimura, Atsushi   ; Harada, Hideo   ; Chiba, Satoshi*; Aritomo, Yoshihiro*; Otsuki, Tsutomu*; Hagino, Koichi*

Fragment mass distributions for fission after the full-momentum transfer have been measured at the JAEA tandem for the reactions Si,P,S,Ar, Ca + U at the bombarding energies around the Coulomb barriers in order to investigate the effects of nuclear orientation on the fusion-fission and quasi-fission process. It was observed that the mass distribution goes symmetric to asymmetric with decreasing bombarding energy. A remarkable change occurs around sub-barrier energies. The variation of the mass distribution with reaction energy results from the orientation effects of the deformed target nucleus U on the reaction. At deep sub-barrier energy, where only polar collisions lead to nuclear contact, most of the reactions with the projectile and target captured inside the Coulomb barriers disintegrate as quasi-fission through the asymmetric fission valley. At the high bombarding energy, where equatorial collisions dominate, the system has larger probability to form the compound nucleus and has symmetric mass distribution peculiar to fusion-fission. In the conference, the status of the other research activities of neutron-induced fission at J-PARC and multi-nucleon transfer fission at JAEA-Tandem will also be presented.