ABSTRACT :The 4 π INDRA multi-detector was exploited to study heavy ion collisions at Fermi energies in order to explore the so-called symmetry energy, which is the isospin dependence of the nuclear matter Equation of State. Our study has first focused on new data analysis techniques in order to select quasi-projectile sources compatible with a statistical de-excitation (“Sel” variable) and to sort quasi-fusion events and quasi-projectile/quasi-target events (variable “Vbigiso”). This first step was obtained with data from Xe+Sn and Au+Au reactions at different bombarding energies, specifically studying fragments and particles detected on the forward side of the reaction centre-of-mass. By analyzing the centre-of-mass forward light charged particles and fragments (Z>2) production in the reactions 136,124Xe+124,112Sn at 32 MeV/nucleon, corresponding to the fifth INDRA campaign at GANIL, we have confirmed the presence of isospin diffusion between projectile and target. We have shown that the magnitude of the diffusion increases with the collision violence, corresponding to increasing centrality. The experimental results were compared to theoretical predictions using both a phenomenological event generator, and the BNV/SMF transport model. A new variable is proposed to estimate the density dependence of the symmetry energy at sub-saturation densities. The first comparison with the BNV/SMF model shows that the Asy-stiff equation of state appears compatible with our data.
محمد كبتول | Mohammad KABTOUL | 895