MASS DEPENDENCE OF THE DISAPPEARANCE OF FLOW IN NUCLEAR COLLISIONS

The disappearance of collective flow in nucleus-nucleus collisions occ urs at an incident energy (E(bal)) where the attractive scattering dom inant at low energies balances the repulsive scattering dominant at hi gh energies. We have performed the first systematic study of the entra nce-channel mass dependence of the disappearance of flow and hence E(b al). The new data presented for the C+C, Ne+Al, Ar+Sc, and Kr+Nb syste ms show that E(bal) scales as A-1/3 where A is the mass of the combine d system. Boltzmann-Uehling-Uehlenbeck model calculations show trends which are in qualitative agreement with these new results.