Light particle probes of expansion and temperature evolution: Coalescence model analyses of heavy ion collisions at47A MeV

Abstract

The reactions C-12 + Sn-116, Ne-22 + Ag, Ar-40 + Mo-100, and Zn-64 + Y-89 have been studied at 47A MeV projectile energy. For these reactions the most violent collisions lend to increasing amounts of fragment and light particle emission as the projectile mass increases. This is consistent with quantum molecular dynamics (QMD) model simulations of the collisions. Moving source fits to the light charged particle data have been used to gain a global view of the evolution of the particle emission,Comparisons of the multiplicities and spectra of light charged particles emitted in the reactions with the four different projectiles indicate a common emission mechanism for early emitted ejectiles even though the deposited excitation energies differ greatly. The spectra for such ejectiles can be characterized as emission in the nucleon-nucleon frame. Evidence that the He-3 yield is dominated by this type of emission and the role of the collision dynamics in determining the H-3/He-3 yield ratio are discussed. Self-consistent coalescence model analyses are applied to the light cluster yields, 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. These analyses exploit correlations between ejectile energy and emission time, suggested by the QMD calculations. In this analysis the degree of expansion of the emitting system is found to increase with increasing projectile mass. The double isotope yield ratio temperature drops as the system expands. Average densities as low as 0.36 rho(0) are reached at a time near 100 fm/c after contact. Calorimetric methods were used to derive the mass and excitation energy of the excited nuclei which are present after preequilibrium emission. The derived masses range from 102 to 116 u and the derived excitation energies increase from 2.6 to 6.9 MeV/nucleon with increasing projectile mass. A caloric curve is derived for these expanded A similar to 110 nuclei. This caloric curve exhibits a plateau at temperatures near 7 MeV. The plateau extends from similar to 3.5 to 6.9 MeV/nucleon excitation energy.