Temperature measurements in Xe+Cu at 30 MeV/nucleon: Size effects in the caloric curve

Results of experiments performed to investigate the Xe+Cu 30 MeV/nucleon reaction are presented. The decay products coming from the disassembly of the unique source formed in central collisions and those coming from the decay of the quasiprojectile in peripheral and midperipheral ones have been identified through a careful data selection taking into account the experimental efficiency distortion on energy and angular distributions. The nuclear temperatures of these decaying systems have been measured from the relative isotopic abundances; the excitation energies of the fragment sources have been extracted by means of model calculations. The results have been compared to those obtained in the study of the Au+Au 35 MeV/nucleon in order to probe the effects of the finite size of the intermediate mass fragment emitting source on the relationship between its excitation energy and temperature. The studied fragment emitting sources have mass A₁≃130, A₂≃200, A₃≃300; moreover, the A₂ system have been investigated via two different reaction channels: the quasiprojectile of peripheral Au+Au and the unique fused system of the Xe+Cu central collisions. The relationship between temperature and excitation energy seems to be almost independent on the size of the emitting source and on the reaction entrance channel. On the contrary a weak dependence arises when individual thermometers are considered.