Microscopic calculation of nuclear dissipation

Journal Article · Thu Jan 01 04:00:00 EST 1976 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PhysRevC.13.209· OSTI ID:4076408

Koonin, S. E.; Nix, J. R.

By use of a time-dependent wave function of the BCS form, we compute microscopically the energy dissipated for a system with a monopole pairing force moving under the influence of a time-dependent single-particle potential. Quasiparticle generation and coupling of the two-quasiparticle modes of the system are included automatically and provide contact with the Landau-Zener formula. The single-particle potential is related to nuclear shapes generated by viscous hydrodynamical calculations of a fissioning $sup 236$U nucleus. We attempt to determine the energy dissipated between the saddle point and scission point by requiring that at the scission point the energy dissipated in the microscopic calculations equal that dissipated in the macroscopic hydrodynamical calculations. This procedure leads to 34 MeV of dissipated energy, which is almost twice the value of 18 MeV obtained from macroscopic hydrodynamical calculations that reproduce experimental fission-fragment kinetic energies. The corresponding value of the nuclear viscosity coefficient determined from the microscopic calculations is 0.04 TP, compared to 0.015+-0.005 TP obtained from the macroscopic hydrodynamical calculations. The viscosity coefficient determined from the microscopic calculations is even larger if the dissipated energies are compared at a finite scission neck radius. As a possible resolution of this discrepancy, we propose that level splittings arising from axially asymmetric and reflection-asymmetric deformations during the descent from the saddle point to scission reduce the energy dissipation and make the nuclei only moderately viscous. (AIP)

• Research Organization: Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-027779
• OSTI ID: 4076408
• Journal Information: Physical Review. C, Nuclear Physics, Journal Name: Physical Review. C, Nuclear Physics Journal Issue: 1 Vol. 13; ISSN 0556-2813; ISSN PRVCAN
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

*FISSION-- NUCLEAR REACTION KINETICS
*URANIUM 236-- FISSION
643506*
BCS THEORY
DISSIPATION FACTOR
N69162 --Physics (Nuclear
Theoretical)--Nuclear Properties & Reactions
A >= 220--Nuclear Reactions & Scattering--Spontaneous & Induced Fission:734
N69260* --Physics (Nuclear)--Nuclear Theory--Spontaneous & Induced Fission
NUCLEAR REACTIONS
NUCLEAR STRUCTURE
PAIRING INTERACTIONS
SINGLE-PARTICLE MODEL
WAVE FUNCTIONS