Vlasov-Uehling-Uhlenbeck theory of medium energy heavy ion reactions: Role of mean field dynamics and two body collisions
The role of nonequilibrium and quantal effects in fast nucleus-nucleus collisions is studied via the Vlasov-Uehling-Uhlenbeck theory which includes the nuclear mean field dynamics, two-body collisions, and Pauli blocking. The intranuclear cascade model, where the dynamics is governed by independent NN collisions, and the Vlasov equation, where the nuclear mean field determines the collision dynamics, are also studied as reference cases. The Vlasov equation (no collision term) yields single particle distribution functions which--after the reaction--are only slightly modified in momentum space; even in central collisions, transparency is predicted. This is in agreement with the predictions of the quantal time-dependent Hartree-Fock method. In contrast, large momentum transfer is obtained when the Uehling-Uhlenbeck collision term is incorporated; then the final momentum distribution is nearly spherically symmetric in the center of mass and a well-equilibrated nuclear system is formed: the nuclei stop each other; the translational kinetic energy is transformed into randomized microscopic motion. The Vlasov-Uehling-Uhlenbeck theory is supplemented with a phase space coalescence model of fragment formation. Calculated proton spectra compare well with recent data for Ar(42, 92, and 137 MeV/nucleon) + Ca. Also the total yields of medium mass fragments are well reproduced in the present approach. The mean field dynamics without two-body collisions, on the other hand, exhibits forward peaked proton distributions, in contrast to the data. The cascade approach underpredicts the yields of low energy protons by more than an order of magnitude.
- Research Organization:
- National Superconducting Cyclotron Laboratory, Department of Physics and Astronomy and Department of Chemistry, Michigan State University, East Lansing, Michigan 48824
- OSTI ID:
- 5938270
- Journal Information:
- Phys. Rev. C; (United States), Vol. 31:5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HEAVY ION REACTIONS
BOLTZMANN-VLASOV EQUATION
MEAN-FIELD THEORY
TWO-BODY PROBLEM
DISTRIBUTION FUNCTIONS
HARTREE-FOCK METHOD
NUCLEAR CASCADES
NUCLEON-NUCLEON INTERACTIONS
PHASE SPACE
PROTON SPECTRA
TIME DEPENDENCE
BARYON-BARYON INTERACTIONS
CHARGED-PARTICLE REACTIONS
DIFFERENTIAL EQUATIONS
EQUATIONS
FUNCTIONS
HADRON-HADRON INTERACTIONS
INTERACTIONS
MANY-BODY PROBLEM
MATHEMATICAL SPACE
NUCLEAR REACTIONS
PARTIAL DIFFERENTIAL EQUATIONS
PARTICLE INTERACTIONS
SPACE
SPECTRA
653003* - Nuclear Theory- Nuclear Reactions & Scattering
653007 - Nuclear Theory- Nuclear Models- (-1987)