  With stochastic transport simulations we study in detail central and
peripheral collisions at Fermi energies and suggest new observables, sensitive
to the symmetry energy below normal density. As such we identify on one hand
the isospin imbalance ratio, i.e. the relative amount of isospin equilibration
in binary, peripheral reactions of nuclei with different isospin, as a function
of the energy loss, which is sensitive to isospin diffusion; on the other hand
the isospin asymmetry of an intermediate mass fragment (IMF) in symmetric
collisions in ternary reactions, or more particularly, the ratio of the IMF to
the residue asymmetry, which is sensitive to isospin migration.
