Semiclassical simulations of peripheral heavy-ion collisions at Fermi Energies and the sensitivity to the density dependence of the nuclear symmetry energy

During the last several years we have undertaken a systematic study of heavy residues formed in quasi-elastic and deep-inelastic collisions near and below the Fermi energy. The original motivation of these studies was the understanding and the optimization of the production of very neutron-rich rare isotopes in these collisions [1,2,3]. In parallel, we became motivated to pursue these studies further in hopes of extracting information on the properties of the nuclear effective interaction as manifested in the mechanism of nucleon exchange and the course towards N/Z equilibration [4]. Recently, we focussed our interest on the possibility of extracting information on the isospin part of the nuclear equation of state (EOS) by comparing our heavy residue data to detailed calculations using microscopic models of heavy-ion collisions at these energies [5]. After some initial efforts with transport-type codes (BUU, BNV), we turned our attention to the quantum molecular dynamics approach (QMD). We have performed detailed calculations using the recent version of the constrained molecular dynamics code CoMD of A. Bonasera and M. Papa [6,7]. This code is especially designed for reactions near and below the Fermi energy. It implements an effective interaction corresponding to a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential (Fig. 1) [8]. While not using antisymmetrized N-body wave functions, CoMD imposes a constraint in the phase space occupation for each nucleon, effectively restoring the Pauli principle at each time step of the Figure 1. Density dependence of the nuclear symmetry energy Csym(ρ) corresponding to the choices of the nucleon-nucleon symmetry potential in the CoMD code: blue (asy-soft), red: (asy-stiff), green (super asy-stiff) and grey line (no-symm). The black line represents the form 31.6(ρ/ρ0) consistent with the isoscaling analysis of IMFs from central heavy-ion collisions [8].