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

Effects of nuclear orientation on fission fragment mass distributions in the reaction of Si-30 + U-238 were investigated. The mass distributions showed a Gaussian shape in the above barrier region, having a character of fusion-fission. At the sub-barrier energies, the asymmetric fission component around A(L)/A(H) approximate to 90/178 appears, representing quasifision. The measured evaporation residue cross sections for Si-30 + U-238 in [1] have also suggested the competition between fusion and quasifission at sub-barrier region, whereas the fusion is the main process in the above barrier region. These results suggest an influence of orientation effects of the deformed target nuclei on the reaction. Discussion will be given on the difference in the mass distributions between Si-30 + U-238 and S-36 + U-238.