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Title: Langevin model of low-energy fission

Journal Article · · Physical Review C
 [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Since the earliest days of fission, stochastic models have been used to describe and model the process. For a quarter century, numerical solutions of Langevin equations have been used to model fission of highly excited nuclei, where microscopic potential-energy effects have been neglected. In this paper I present a Langevin model for the fission of nuclei with low to medium excitation energies, for which microscopic effects in the potential energy cannot be ignored. I solve Langevin equations in a five-dimensional space of nuclear deformations. The macroscopic-microscopic potential energy from a global nuclear structure model well benchmarked to nuclear masses is tabulated on a mesh of approximately 107 points in this deformation space. The potential is defined continuously inside the mesh boundaries by use of a moving five-dimensional cubic spline approximation. Because of reflection symmetry, the effective mesh is nearly twice this size. For the inertia, I use a (possibly scaled) approximation to the inertia tensor defined by irrotational flow. A phenomenological dissipation tensor related to one-body dissipation is used. A normal-mode analysis of the dynamical system at the saddle point and the assumption of quasiequilibrium provide distributions of initial conditions appropriate to low excitation energies, and are extended to model spontaneous fission. A dynamical model of postscission fragment motion including dynamical deformations and separation allows the calculation of final mass and kinetic-energy distributions, along with other interesting quantities. The model makes quantitative predictions for fragment mass and kinetic-energy yields, some of which are very close to measured ones. Varying the energy of the incident neutron for induced fission allows the prediction of energy dependencies of fragment yields and average kinetic energies. With a simple approximation for spontaneous fission starting conditions, quantitative predictions are made for some observables which are close to measurements. In conclusion, this model is able to reproduce several mass and energy yield observables with a small number of physical parameters, some of which do not need to be varied after benchmarking to 235U (n, f) to predict results for other fissioning isotopes.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1394975
Alternate ID(s):
OSTI ID: 1378409
Report Number(s):
LA-UR-17-23344
Journal Information:
Physical Review C, Vol. 96, Issue 3; ISSN 2469-9985
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 77 works
Citation information provided by
Web of Science

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Cited By (9)

Correlated transitions in TKE and mass distributions of fission fragments described by 4-D Langevin equation journal February 2019
235 U(n, f) Independent fission product yield and isomeric ratio calculated with the statistical Hauser–Feshbach theory journal April 2018
r -process nucleosynthesis: connecting rare-isotope beam facilities with the cosmos journal July 2019
Fission dynamics in systems of intermediate fissility journal October 2019
Review on the progress in nuclear fission—experimental methods and theoretical descriptions journal September 2018
Role of channel temperature and mass window in the binary breakup of U * 236 journal September 2019
Formation and distribution of fragments in the spontaneous fission of 240 Pu journal December 2017
Correlated prompt fission data in transport simulations journal January 2018
Correlated Prompt Fission Data in Transport Simulations text January 2017