DYNAMICS OF RADIAL COLLECTIVE ENERGY IN NEAR CENTRAL COLLISIONS FOR 1A GEV AU+C

Transverse kinetic energies of individual fragments have been measured over a broad range of emitter excitation energies for the reaction 1A GeV Au+C. For excitation energies leading to large intermediate mass fragment multiplicities, these transverse energies require large colle ctive radial expansion of the emitting systems. However, the tradition al decomposition of the transverse energy into a thermal component and a Coulomb and collective component proportional to the fragment mass cannot account for this expansion. Expansion velocities show an increa se with decreasing fragment Z and thus indicate fractionation of the c ollective energy for the expanding system. This collective energy incr eases with emitter excitation up to about 50% of the energy deposited for a nuclear system with total energy similar to 12A MeV. The bulk of the collective energy is carried away by ejectiles of Z less than or equal to 3.