Investigation of fission properties and evaporation residue measurement in the reactions using ²³⁸U target nucleus

¹ Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
² GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany
³ Institut für Kernphysik, Goethe-Universität Frankfurt, 60438 Frankfurt am Main, Germany
⁴ Department of Nuclear Physics and Biophysics, Comenius University, 84248 Bratislava, Slovakia
⁵ Flerov Laboratory of Nuclear Reactions, 141 980 Dubna, Russia
⁶ Higher Institute of Technologies and Applied Sciences, Habana 10400, Cuba
⁷ Institut für Radiochemie, Technische Universität München, 85748 Garching, Germany
⁸ Department of Physics, Tohoku University, Sendai 980-8597, Japan
⁹ Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826, Japan
¹⁰ High Energy Accelerator Organization (KEK), Tsukuba 305-0801, Japan

^a e-mail: nishio.katsuhisa@jaea.go.jp

Abstract

Fragment mass distributions for fission after full momentum transfer were measured in the reactions of ³⁰Si,^{34,36 S,31}P,⁴⁰Ar + ²³⁸U at bombarding energies around the Coulomb barrier. Mass distributions change significantly as a function of incident beam energy. The asymmetric fission probability increases at sub-barrier energy. The phenomenon is interpreted as an enhanced quasifission probability owing to orientation effects on fusion and/or quasifission. The evaporation residue (ER) cross sections were measured in the reactions of ³⁰Si + ²³⁸U and ³⁴S + ²³⁸U to obtain information on fusion. In the latter reaction, significant suppression of fusion was implied. This suggests that fission events different from compound nucleus are included in the masssymmetric fragments. The results are supported by a model calculation based on a dynamical calculation using Langevin equation, in which the mass distribution for fusion-fission and quasifission fragments are separately determined.