Shell damping energy studied from the measurement of fission fragment mass distribution

Lguillon, R.; Nishio, Katsuhisa   ; Hirose, Kentaro  ; Orlandi, R.  ; Makii, Hiroyuki   ; Nishinaka, Ichiro; Ishii, Tetsuro  ; Tsukada, Kazuaki  ; Aritomo, Yoshihiro*; Chiba, Satoshi*; Otsuki, Tsutomu*

In a model for fusion between heavy-nuclei and survival probability of the excited compound nucleus to calculate a cross section to produce super-heavy elements, a shell damping energy which represents the degree of washing out the shell-correction energy with excitation energy is one of the key parameters. This value is also crucial to calculate fission properties such as fragment mass distribution. The value was originally determined from the spacing of the excited energy levels. However, it is still an open question if the value depends on nuclei or is universal over nuclei. We are studying the shell damping energy and its dependence with nuclei by measuring the fission fragment mass distributions and comparing them with a calculation based on the fluctuation-dissipation model where the shell damping energy E is an input parameter. Excited fissioning nuclei were populated by multi-nucleon transfer reactions such as O + Th,U, and excitation energy dependence of the fission fragment mass distributions was measured up to E* = 50 MeV. The experiment was carried out at the JAEA tandem facility. Although the E value obtained in this manner is model dependent, the applied model itself can describe the fusion reaction for the synthesis of SHE, allowing us to give a constrain in the value.