Dynamics of radial collective energy in near central collisions for $1A\mathrm{GeV}$ $\mathrm{A}\mathrm{u}+\mathrm{C}$

Transverse kinetic energies of individual fragments have been measured over a broad range of emitter excitation energies for the reaction $1A\mathrm{GeV}$ $\mathrm{A}\mathrm{u}+\mathrm{C}.$ For excitation energies leading to large intermediate mass fragment multiplicities, these transverse energies require large collective radial expansion of the emitting systems. However, the traditional 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 increase with decreasing fragment $Z$ and thus indicate fractionation of the collective energy for the expanding system. This collective energy increases with emitter excitation up to about 50% of the energy deposited for a nuclear system with total energy $\sim 12A\mathrm{MeV}.$ The bulk of the collective energy is carried away by ejectiles of $Z<~3.$