TEMPERATURE AND THERMODYNAMIC INSTABILITIES IN HEAVY-ION COLLISIONS

We investigate thermodynamic properties and instability conditions in intermediate energy heavy-ion reactions, We define locally thermodynam ic variables, i.e. density, pressure and temperature, directly from th e phase space distribution of a relativistic transport calculation. In particular, temperatures are determined by a fit to two covariant hot Fermi distributions thus taking into account possible anisotropic mom entum configurations. We define instability independent from the nucle ar matter spinodal by the criterion that the effective compressibility becomes negative. The method is applied to a semi-central Au on Au re action at 600 MeV/nucleon. We investigate in particular the center of the participant and the spectator matter. In the latter we find a clea r indication of instability with conditions of density and temperature that are consistent with experimental determinations. (C) 1997 Elsevi er Science B.V.