Étude de la fission avec PISTA et VAMOS par transfert multi-nucléons en cinématique inverse

More than eighty-five years after its discovery, a complete description of the fission process remains a challenge. Progress in this field requires new experimental data on exotic fissioning systems that cannot be accessed through direct neutron-induced reactions, but are essential for advancing our understanding of the fission mechanism, as well as for applications in astrophysics and reactor modeling. The use of surrogate reactions in inverse kinematics allows both the study of exotic fissioning systems and the isotopic identification of fission fragments. However, the characterization of the fissioning system in terms of isotopic content (A, Z) and the precise determination of its excitation energy is of paramount importance, though very challenging. In this thesis, the fission process was investigated at GANIL using a newly developed target-like residue detection system, PISTA (Particle Identification Silicon Telescope Array), coupled to the VAMOS spectrometer. This thesis presents the data analysis from the first experiment with PISTA, which employed multi-nucleon transfer reactions in inverse kinematics using a 238U beam at Coulomb-barrier energies impinging on thin 12C targets. The analysis of this experiment shows enhanced identification of target-like nuclei, enabling a characterization of the fissioning systems in terms of mass, atomic number, and excitation energy, with an energy resolution improved by about a factor of two compared to the previous setup. Twenty transfer channels have been identified and analyzed, with the production of associated cross-sections and excitation-energy spectra. Fission probabilities as a function of the excitation energy of the fissioning system were measured, and the corresponding fission barrier heights were extracted. The results were compared with both literature data and model predictions obtained with TALYS. A new approach was proposed to estimate the angular-momentum distribution of fissioning systems from experimental excitation functions, providing an alternative way to access this information.