Isospin Dynamics in Fragmentation Reactions at Fermi Energies

In this work we have studied the neutrons and protons dynamical behavior in two fragmentation reaction: ⁵⁸Fe+⁵⁸Fe (charge asymmetric, N/Z = 1.23) and ⁵⁸Ni+⁵⁸Ni (charge symmetric, N/Z = 1.07). We note that isospin dynamic processes take place also in the symmetric system ⁵⁸Ni+⁵⁸Ni, that produce more asymmetric fragments and residual nuclei. This is a consequence of the pre-equilibrium phase: we observe a competition between pre-equilibrium evaporation and the phenomenon of the isospin-migration, which is a consequence of the EOS (nuclear equation of state) symmetry term. We have simulated the collision with two different EOS: asy-stiff and asy-soft. Some difference has been noticed, especially about the fragment charge asymmetry. A check of isospin effects has also been done trying to correlate fragment asymmetry with dynamical quantities at the freeze-out time.