Negative heat capacity for hot nuclei using formulation from the microcanonical ensemble INDRA Collaboration

By using freeze-out properties of multifragmenting hot nuclei produced in quasifusion central ^129Xe+^natSn 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 4π 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 signs a first order phase transition for finite systems is observed and confirms previous results using a different method.