CALORIC CURVES OF HOT NUCLEI FORMED IN REACTIONS INDUCED BY 50 MEV U XE-129 AND 52-95 MEV/U AR-36 PROJECTILES/

The reactions Xe-129 + Sn-119 at 50 MeV/u and Ar-36 + Ni-58 from 52 to 95 MeV/u were studied with the 4 pi array INDRA. The quasi-projectile s were reconstructed from peripheral to central collisions, and their excitation energies range from 2 to 20 MeV/nucleon. The apparent tempe ratures obtained from the kinetic energy distribution of light particl es, from the double ratios of isotopic yields and from the relative po pulations of excited states, respectively, differ much from each other . Two statistical models, taking into account the detailed energy leve l structure of decaying primary fragments, can explain these differenc es. The relationship between the initial temperature and excitation en ergy does not exhibit any discontinuity of the caloric capacity: the l iquid-gas phase transition is gradual.