Isospin effects and symmetry energy studies with INDRA
Abstract.
The equation of state of asymmetric nuclear matter is still controversial, as predictions at sub-saturation as well as above normal density widely diverge. We discuss several experimental results measured in heavy-ion collisions with the INDRA array in the incident energy range 5–80 A MeV. In particular an estimate of the density dependence of the symmetry energy is derived from isospin diffusion results compared with a transport code: the potential part of the symmetry energy linearly increases with the density. We demonstrate that isospin equilibrium is reached in mid-central collisions for the two reactions Ni+Au at 52 A MeV and Xe + Sn at 32 A MeV. New possible variables and an improved modelization to investigate symmetry energy are discussed.
PhD thesis: " Search for isospin effects in heavy-ion collisions 136,124Xe + 124,112Sn at 32 A.MeV"
ABSTRACT:
The 4π 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.
Chemistry of nuclear particle production in 32 A MeV 136,124Xe+124,112Sn reactions and nuclear symmetry energy
Kabtoul M., Bougault R., Colonna M., Galichet E.
Abstract
Nuclear particle production from peripheral to central events is presented. N/Z gradient between projectile and target is studied using the fact that two reactions have the same projectile+target N/Z and so the same neutron to proton ratio for the combined system and the impact parameter size dependent geometrical overlap region. Data in the forward part of the centre of mass indicates that N/Z equilibration is achieved for impact parameters below 6 fm and a comparison with transport model SMF calculations is done. SMF results agree with the data in average and by using the fragment multiplicity difference between 136 Xe+112 Sn and 124 Xe+124 Sn systems it seems possible to characterize the density dependence of the symmetry energy.
