Steve Coll's pictureSteve Coll

Hope College

Dr. Mader

Supported by the Michigan Space Grant Consortium

The nuclear equation of state (EoS) is a mathematical representation of inter-nuclear interactions. By refining the representation, a better understanding of these interactions under extreme conditions may provide clues to such astrophysical phenomena as the formation of neutron stars. To recreate in a laboratory setting the extreme conditions present in the early stages of the universe and in stellar evolution, nucleons are collided at high energy. The resulting compression and temperatures in the system are comparable to those present in stellar formation. Because of the small sizes involved, direct measurements of temperature and pressure are not possible. Thus, insight in the nuclear EoS under a wide range of temperatures and pressures can only be obtained by comparison of model and experimental results.

The Boltzmann-Ueling-Uhlenbeck (BUU) model is a semi-classical transport model that is used to study nuclear collisions. The colliding nuclei are represented as individual test particles (nucleons) which follow classical trajectories in a nuclear mean field potential, which contains information about the nuclear EoS. Classical billiard-ball collisions may occur if two nucleons pass close enough to one another. The Pauli-exclusion principle is employed and forbids any collision which would cause more than one nucleon to occupy the same state.

The model has previously been shown to obey the classical conservation laws of energy and momentum. However, it has also been shown that angular momentum is not necessarily conserved. Various algorithms were tested which would conserve the angular momentum of the system. The methods, which employ several different basic assumptions, affect observable quantities such as the collective flow. The extent of these effects are being currently examined.