Effects of multichance fission on fission fragment mass distributions at high energies

Tanaka, Shoya; Hirose, Kentaro  ; Nishio, Katsuhisa   ; Aritomo, Yoshihiro*

Recently, fission-fragment mass distributions (FFMDs) were measured for U, Np, and Pu populated in the excitation-energy range from 10 to 60 MeV by multinucleon transfer channels in the reaction O + U at the Japan Atomic Energy Agency tandem facility. A persistence of predominantly asymmetric FFMDs was observed up to the highest measured excitation energy for all the studied nuclides. To understand this behavior, we use the fluctuation-dissipation model and employ Langevin equations to obtain FFMDs and clarify multichance fission (MCF) effects. FFMDs are calculated for twenty-nine compound nuclides Th, Pa, U, Np and Pu with the excitation energy range from 15 to 55 MeV. The calculation results show generally good agreement with experimental data. It was shown that a reliable understanding of the observed FFMDs can be obtained only by invoking MCF.