Observable effects of symmetry energy in heavy-ion collisions at intermediate energies

Within an isospin-dependent transport model for nuclear reactions induced by neutron-rich nuclei, we perform a comparative study of 100Sn+124Sn and 100Zn+124Zn reactions at beam energies of 30 MeV/nucleon and 400 MeV/nucleon to identify optimal experimental conditions and observables for investigating the equation of state (EOS) of neutron-rich matter at the Rare Isotope Accelerator (RIA). Several observables known to be sensitive to the density dependence of the symmetry energy are examined as a function of impact parameter for both reaction systems. In particular, the strength of isospin transport/diffusion is studied by using rapidity distributions of free nucleons and their isospin asymmetries. An approximate isospin equilibrium is established even for peripheral collisions with a very soft symmetry energy at 30 MeV/nucleon. At 400 MeV/nucleon, however, a strong isospin translucency is observed even in most central collisions with either soft or stiff symmetry energies. Origins of these observations and their implications to determining the EOS of neutron-rich matter at the RIA are discussed