Effects of nuclear orientation on fusion and fission process for reactions using 238U target nucleus

Fission fragment mass distributions in the reaction of Si-30+U-238 were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, asymmetric fission mode peaked at A(L)/A(H) approximate to 90/178 was observed. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by Si-30+U-238. The cross-section for (263)Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for (264)Sg measured at the sub-barrier energy is smaller than the calculation, indicating the presence for quasifission. The fragment mass distributions are compared to those for (36)s+U-238 and Ar-40+U-238.