FREEZE-OUT CONFIGURATION IN MULTIFRAGMENTATION

The excitation energy and the nuclear density at the time of breakup a re extracted for the alpha+Au-197 reaction at beam energies of 1 and 3 .6 GeV/nucleon. These quantities are calculated from the average relat ive velocity of intermediate mass fragments (IMF) at large correlation angles as a function of the multiplicity of IMFs using a statistical model coupled with many-body Coulomb trajectory calculations. The Coul omb component upsilon(c) and thermal component upsilon0 are found to d epend oppositely on the excitation energy, IMFs multiplicity, and free ze-out density. These dependencies allow the determination of both the volume and the mean excitation energy at the time of breakup. It is f ound that the volume remained constant as the beam energy was increase d, with a breakup density of about rho0/7, but that the excitation ene rgy increased 25% to about 5.5 MeV/nucleon.