Study of nuclear stopping in central collisions at intermediate energies.

Nuclear stopping has been investigated in central nuclear collisions at intermediate energies by analyzing kinematically complete events recorded with the help of the 4π multidetector INDRA for a large variety of symmetric systems. It is found that the mean isotropy ratio defined as the ratio of transverse to parallel momenta (energies) reaches a minimum near the Fermi energy, saturates or slowly increases depending on the mass of the system as the beam energy increases, and then stays lower than unity, showing that significant stopping is not achieved even for the heavier systems. Close to and above the Fermi energy, experimental data show no effect of the isospin content of the interacting system. A comparison with transport model calculations reveals that the latter overestimates the stopping power at low energies.

Phase diagram of the charged lattice-gas model with two types of particles.

A lattice-gas model with two types of particles, a particle-dependent short-range coupling and a long-range repulsive Coulombic interaction, is introduced. The phase diagram of an isolated finite system of 129 particles is constructed using the bimodality properties of the observables' distribution. We show that this generic Hamiltonian, with couplings optimized on the properties of the atomic nucleus, exhibits a specific phase diagram including, together with the well-known liquid-gas phase transition, a segregation phase that can be assimilated to nuclear fission.

Isoscaling as a measure of symmetry energy in the lattice gas model.

The energetic properties of nuclear clusters inside a low-density, finite-temperature medium are studied with a lattice gas model including isospin dependence and Coulomb forces. Important deviations are observed with respect to the Fisher approximation of an ideal gas of noninteracting clusters, but a simple modified energy-density functional can still describe the global energetics. The multifragmentation regime is dominated by combinatorial effects, but the isoscaling of the largest fragment appears to be a promising observable for the experimental measurement of the symmetry energy.