Role of Multichance Fission in the Description of Fission-Fragment Mass Distributions at High Energies

Abstract

Fission-fragment mass distributions were measured for ^{237-240}U, ^{239-242}Np, and ^{241-244}Pu populated in the excitation-energy range from 10 to 60 MeV by multinucleon transfer channels in the reaction ^{18}O+^{238}U at the Japan Atomic Energy Agency tandem facility. Among them, the data for ^{240}U and ^{240,241,242}Np were observed for the first time. It was found that the mass distributions for all the studied nuclides maintain a double-humped shape up to the highest measured energy in contrast to expectations of predominantly symmetric fission due to the washing out of nuclear shell effects. From a comparison with the dynamical calculation based on the fluctuation-dissipation model, this behavior of the mass distributions was unambiguously attributed to the effect of multichance fission.

Isotopic fission-fragment distributions of U238, Np239, Pu240Ramos1, Caamaño2, Farget3 et al. 2018Phys. Rev. C415150View full textAdd to dashboardCite

“…Instead, an effective decrease of E x at the saddle point due to pre-saddle neutron evaporation may explain such behavior, as shown in Refs. [37,40].…”

First Direct Measurement of Isotopic Fission-Fragment Yields of U239

“…The complete fission-fragment identification was not feasible due to the low kinetic energy of the fission products. The use of surrogate reactions gave access to the study of a wider range of compound nu- * Email address: diego.ramos@ganil.fr † Present address: ILL, F-38042 Grenoble Cedex 9, France ‡ Present address: CEA, DAM, DIF, F-91297 Arpajon, France clei, otherwise inaccessible [19][20][21]. The use of inverse kinematics allowed the direct measurement of the atomic number of complete fission-fragment distributions [22].…”

Fission of compound nuclei and the developments of microscopic fission theory

“…TD-GCM采用温度相关的裂变位垒计算碎片分布是十分 需要的. 复合核裂变的实验研究已经积累了很多的数 据, 人们已经注意到特别是高激发态中多步裂变过程 对碎片分布的影响 [49] . 所以实验需要更多地测量初始 裂变产物分布来检验理论模型.…”