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Matière Nucléaire, GANIL E209, GANIL E210; International audience; Reaction mechanisms have been studied for two nearly symmetrical systems of different total mass, between 25 and 74 AMeV. It is shown that collisions are mostly binary whatever the system mass and the bombarding energy. From the slowing-down of the partners, it is possible to establish the continuous evolution from quasielastic to (completely) damped collisions. It turns out that results are independent of the total system mass if involved energies are expressed in AMeV. The occurrence of mid-rapidity emission is also considered and may be used to establish a link between mechanisms observed at low and high bombarding energy. Part of it corresponds to a fast decay of outgoing partners.

The hard photon spectrum emitted in heavy-ion collisions is analyzed in the light of dynamical phase-space considerations to infer information on the thermodynamical properties of hot and dense nuclear matter. Energy spectrum, angular distribution and two-photon interference pattern converge to indicate the existence of two distinct photon sources shining during the thermalization phase of the participant zone.

The reactions Kr-84+Au-197 and Kr-84+U-nat were studied at an incident energy of E/A = 150 MeV employing the large-volume neutron multiplicity meter ORION, The observed correlations between the atomic number of projectile-like nuclei (PLN) and neutron multiplicity indicate large deposits of excitation energies in the primary fragments, Angular correlations between fragments from the fission of target-like nuclei (TLN) and secondary PLN show a memory of the reaction plane. No indications for spin effects were found in the TLN-fission fragment distribution.

The violence of collisions induced by Pb-208 projectiles bombarding a Au-197 target at 29 MeV/u has been deduced by detecting the accompanying neutrons. With this filter, the temperature of the projectile-like fragments formed in very dissipative collisions has been extracted from the slope of the alpha-particle energy spectra. Temperatures of the order of 7 MeV are found, in very good agreement with the energy dissipations deduced from an energy balance assuming binary kinematics. The associated neutron multiplicities are well reproduced by a standard evaporation model, despite the dissociation into intermediate mass fragments observed in previous experiments. However, the measured temperatures exceed by a significant amount the limits predicted by theoretical calculations.

Gamma-ray energy spectra have been measured for the 16 O + 118 Sn reaction at incident beam energies of 200 and 280 MeV. Comparing the experimentally obtained spectra with statistical-model calculations shows that the width of the isovector giant dipole resonance saturates beyond excitation energies of 165 MeV in the compound nucleus.

The hard photon spectrum emitted in heavy-ion collisions is analyzed in the light of dynamical phase-space considerations to infer information on the thermodynamical properties of hot and dense nuclear matter. Energy spectrum, angular distribution and two-photon interference pattern converge to indicate the existence of two distinct photon sources shining during the thermalization phase of the participant zone.