Effects of nuclear orientation on fission fragment mass distributions in the reactions using actinide target nuclei

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

The influence of nuclear deformation of U target nucleus on fusion and fission process was investigated. The study was motivated by larger cross-sections to produce super-heavy nuclei in reactions using actinide target nuclei, compared to those using lead or bismuth target nuclei. We have measured fission fragment mass distributions in the reaction of Si,P,S,Ar + U at JAEA tandem facility. We observed strong variation of the distributions on bombarding energy of projectiles, which indicates that competition between fusion and fission is sensitive to the colliding angle of the projectile to the symmetric axis of U. We also measured the evaporation residue cross-sections for Si+U and S+U as a direct evidence for fusion. The experiment was carried out at GSI. The results showed that fusion is much hindered in the subbarrier energy, where projectile collides only on the pollar side of the U nucleus, whereas the equatorial collision has smaller fusion hindrance. These results indicate that the initial touching configuration influence the subsequent reaction process.