Negative heat capacity for hot nuclei: Confirmation with formulation from the microcanonical ensemble

By using freeze-out properties of multifragmenting hot nuclei produced in quasifusion central Xe-129 + Sn-nat collisions at different beam energies (32, 39, 45 and 50 AMeV) which were estimated by means of a simulation based on experimental data collected by the 4 pi INDRA multidetector, heat capacity in the thermal excitation energy range 4-12.5 AMeV was calculated from total kinetic energies and multiplicities at freeze-out. The microcanonical formulation was employed. Negative heat capacity which indicates a first order phase transition for finite systems is observed and confirms previous results using a different method.