In dissipative nuclear reactions, an important transfer of energy takes place between the projectile and the target. Part of the initial mechanical energy is stored as thermal energy in the nuclei. To study the behavior of nuclei when this energy increases, two methods based on calorimetry were used : a so-called " 3D calorimetry ", validated and optimized in the present work and another so-called " standard calorimetry ", already used by the scientific community. They allowed to reconstruct the characteristics of hot Quasi-Projectiles, produced in symmetric or quasisymmetric reactions. The advantages and disadvantages of each of these methods, have been studied using two event generators, HIPSE and ELIE, modeling the physical processes occurring during collisions but differing by the scenario of hot nucleus formation. This systematic study allowed to determine at which temperature and which excitation energy per nucleon, nuclei of intermediate mass evolve from a nuclear liquid state to a nuclear gaseous state. The information obtained by the " 3D calorimetry" also allowed to isolate the preequilibrium component. This result was experimentally confirmed by a new use of the isospin degree of freedom (the ratio neutron/proton), as a ' tracer' in the velocity space.
