La formation et la désexcitation de noyaux chauds dans les collisions $^{40}$Ar + $^{197}$Au à 44 et 77 MeV/u. Émission de neutrons, particules chargées légères et fragments complexes.

Abstract : This work is a contribution to the study of the formation and decay of hot nuclei produced in heavy ion collisions at intermediate energies. By studying the system Ar + Au and Ar + Th at 44 MeV/u and 77 MeV/u we first show how to classify events in two groups: peripheral and very dissipative collisions, measuring the number of evaporated neutrons, which depend directly on the violence of the collision. Associated with these neutrons, different deexcitation channels were observed (heavy residues, fission fragments, light charged particles, intermediate mass fragments). The ratio between peripheral and very dissipative collisions was found independent of the system and the same as the one observed at lower incident energy. The most probable neutron multiplicity for very dissipative collisions is not very different at 44 MeV/u and 77 MeV/u. A measurement of the angular distribution of fission fragments and heavy residues was performed. Detected products are essentially associated with large neutron multiplicity and have a cross section close to the one for the very dissipative collisions. The total mass of the fission fragments is close to the mass of the target, while the mass of the heavy residue is much smaller. The backward evaporated light charged particles are also produced in very dissipative collisions. The characteristics of their energy spectra as well as their multiplicities are very similar at 44 MeV/u 77 MeV/u. From the number of evaporated light charged particles, the estimation of the quasi-target excitation energy was done and found to be close to 600 MeV at 44 MeV/u and 77 MeV/u
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André Sokolov. La formation et la désexcitation de noyaux chauds dans les collisions $^{40}$Ar + $^{197}$Au à 44 et 77 MeV/u. Émission de neutrons, particules chargées légères et fragments complexes.. Physique Nucléaire Expérimentale [nucl-ex]. Université Paris 6, 1990. Français. ⟨tel-02067949⟩

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