Effects of nuclear orientation on fusion and fission in the reaction using ²³⁸U target nucleus

K. Nishio¹, H. Ikezoe¹, S. Mitsuoka¹, I. Nishinaka¹, Y. Nagame¹, T. Ohtsuki², K. Hirose² and S. Hofmann^3,4a

¹ Japan Atomic Energy Agency, Tokai, Ibaraki 319-1184, Japan
² Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826, Japan
³ Gesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany
⁴ Institut für Kernphysik, Johann Wolfgang Goethe-Universität, D-60486 Frankfurt am Main, Germany

^a e-mail: Josef Buchmann-Professor Laureatus

Abstract

Fission fragment mass distributions in the reaction of ³⁰Si+²³⁸U were measured around the Coulomb barrier. At the above-barrier energies, the mass distribution showed a Gaussian shape. At the subbarrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at A_L/A_H ≈ 90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections for ³⁰Si+²³⁸U. The cross-section for ²⁶³Sg at the abovebarrier energy agree with the statistical model calculation which assumes that the measured fission cross-section originates from fusion-fission, whereas the one for 264 Sg measured at the sub-barrier energy is smaller than the calculation, which suggests the presence of quasifission.