Evolution of the reaction dynamics in the 58Ni+58Ni system at Fermi energies

Heavy-ion collisions at Fermi energies (20-100 AMeV) represent a transition domain in which reaction mechanisms result from the interplay between mean-field effects and nucleon-nucleon collisions. These reactions proceed through a dynamical phase, corresponding to the initial projectile-target interaction, followed by a statistical de-excitation phase of the hot primary fragments. In peripheral and semiperipheral collisions, the outcome is predominantly binary, producing a quasi-projectile (QP) and a quasi-target (QT). Less frequently, strong deformations of these nuclei can lead to their breakup, which exhibit clear dynamical features. A characteristic of the semiperipheral collisions at Fermi energies is the development of a low-density region connecting the QP and QT, usually called “neck”. Its rupture leads to particle emission at intermediate velocity between those of the QP and QT. These midvelocity emissions are typically more neutron-rich than those originating from statistical evaporation, an effect attributed to isospin transport phenomena, specifically the isospin drift, driven by the density gradient between the neck region and the QP/QT. This thesis investigates the reaction dynamics in semiperipheral collisions for the 58Ni+58Ni system at 32,52 and 74 AMeV by reconstructing the primary sources and examining how their properties evolve with beam energy and centrality. This detailed analysis exploits the features of the INDRA-FAZIA apparatus, which combines the large angular coverage of INDRA with the excellent isotopic resolution of FAZIA. The reconstruction method, based on a calorimetric approach, disentangles the evaporative and midvelocity emissions, allowing the estimation of the size and and excitation energy of the primary sources, namely the excited quasi-projectile QP* and the neck, as a function of centrality and incident energy. For the first time, this approach is applied also to the breakup channel, enabling a direct comparison with the binary one. Moreover, the neutron-to-proton content of the evaporative and midvelocity components is compared, confirming the neutron enrichment of the neck region and providing insight into the isospin drift as a function of beam energy. The obtained results provide detailed information on the properties of the primary QP*, showing how they are affected by midvelocity emission and how they evolve with centrality and beam energy. These findings offer a benchmark for transport model predictions and contribute to a deeper understanding of isospin transport phenomena at Fermi energies.