Professor Joseph Natowitz
Texas A & M University
Cyclotron Institute

Title: "Light Particle Probes of Expansion and Temperature Evolution: Coalescence Model Analyses of Heavy Ion Collisions at 47A MeV"

General Colloquium:
November 11 - 4:00pm Phys 223
(Coffee at 3:30p.m. in room 242)

Abstract
The reactions 12C+ 116Sn, 22Ne+ Ag, 40Ar+ 100Mo and 64Zn + 89Y.have been studied at 47A MeV projectile energy. For the last three reactions the most violent collisions lead to multifragment final states. Calorimetric methods were used to derive the mass and excitation energy of the excited nuclei which are present after pre-equilibrium emission. Self-consistent coalescence model analyses are applied to the light cluster yields. These analyses exploit correlations between ejectile energy and emission time in an attempt to probe emitter source sizes and to follow the evolution of the temperatures and densities from the time of first particle emission to equilibration. In this formulation the initial temperature and the degree of expansion of the emitting system is found to increase with increasing projectile mass. The temperature drops as the system expands. Average densities as low as 0.4 normal density are reached at a time near 100 fm/c. The caloric curve derived for these expanded A~100 nuclei exhibits a plateau.