THE MULTIFRAGMENTATION OF SPECTATOR MATTER

We present the first microscopic calculation of the spectator fragment ation observed in heavy-ion reactions at relativistic energies which r eproduces the slope of the kinetic energy spectra of the fragments as well as their multiplicity, both measured by the ALADIN collaboration. In the past both have been explained in thermal models, however with vastly different assumptions about the excitation energy and the densi ty of the system. We show that both observables are dominated by dynam ical processes and that the system does not pass a state of thermal eq uilibrium. These findings question the recent conjecture that in these collisions a phase transition of first order, similar to that between water and vapor, can be observed. (C) 1997 Elsevier Science B.V.