Effect of viscosity on the dynamics of fission

Journal Article · Tue Jun 01 04:00:00 EDT 1976 · Phys. Rev., C; (United States)

DOI:https://doi.org/10.1103/PhysRevC.13.2385· OSTI ID:7364076

Davies, K T.R.; Sierk, A J; Nix, J R

The effect of ordinary viscosity on nuclear fission is studied by solving classical equations of motion for the time evolution of fissioning nuclei. The collective potential energy is calculated both by means of the usual liquid-drop model and by means of a modified liquid-drop model that takes into account the lowering in the nuclear macroscopic energy due to the finite range of the nuclear force. The collective kinetic energy is calculated for incompressible, nearly irrotational hydrodynamical flow by use of the Werner-Wheeler method. The Rayleigh dissipation function, which describes the transfer of energy of collective motion into internal excitation energy, is calculated under the assumption that nuclear dissipation arises from individual two-body collisions. Prior to scission the nuclear shape is specified in terms of smoothly joined portions of three quadratic surfaces of revolution. After scission the fission fragments are represented by two spheroids with collinear symmetry axes. In addition to slowing the system down and converting some of the collective energy into internal energy, two-body viscosity hinders the formation of a neck. This leads to a more elongated scission configuration and consequently to a smaller final fission-fragment kinetic energy. From a comparison of calculated and experimental most probable fission-fragment kinetic energies for nuclei throughout the periodic table, it is determined that at high excitation energies the average value of the viscosity coefficient ..mu.. is ..mu..=0.015 +- 0.005 TP =9 +- 3 x 10/sup -24/ MeV s/fm/sup 3/, provided that nuclear dissipation arises from two-body collisions. This is about 30% of the value that is required to critically damp the quadrupole oscillations of idealized heavy actinide nuclei. (AIP)

• Research Organization: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
• OSTI ID: 7364076
• Journal Information: Phys. Rev., C; (United States), Journal Name: Phys. Rev., C; (United States) Vol. 13:6; ISSN PRVCA
• Country of Publication: United States
• Language: English

Related Subjects

653006* -- Nuclear Theory-- Spontaneous & Induced Fission
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BINARY FISSION
DEFORMATION
DIFFERENTIAL EQUATIONS
ENERGY
EQUATIONS
EQUATIONS OF MOTION
FISSION
FISSION FRAGMENTS
HYDRODYNAMIC MODEL
KINETIC ENERGY
LIQUID DROP MODEL
MANY-BODY PROBLEM
MATHEMATICAL MODELS
NUCLEAR DEFORMATION
NUCLEAR FRAGMENTS
NUCLEAR MODELS
NUCLEAR POTENTIAL
NUCLEAR REACTIONS
NUMERICAL SOLUTION
PARTICLE MODELS
STATISTICAL MODELS
THERMODYNAMIC MODEL
TWO-BODY PROBLEM
VISCOSITY