Effects of nuclear orientation on fission fragment mass distributions in the reactions of S+U

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

Fragment mass distributions for fission after full momentum transfer were measured for the reaction S,+,U at bombarding energies around the Coulomb barrier. The experiment was carried out by using the sulfur beams supplied by the JAEA tandem accelerator. The experimental data revealed a transition from symmetry to asymmetry mass distributions when the beam energies were decreased from above-barrier to sub-barrier values. The main components of the asymmetric mass distribution are at =200 and 74. The asymmetric fission is attributed to quasifission of the reacting system at polar collisions, whereas the symmetric fission originates from the compound nucleus produced in equatorial collisions. The results suggest a strong influence of orientation effects of the deformed target nuclei on fusion.