  Using an isospin- and momentum-dependent transport model we study the
emission of free nucleons and the nuclear radial flow in central heavy-ion
collisions induced by high energy radioactive beams. The midrapidity
neutron/proton ratio and its transverse momentum dependence are found very
sensitive to the high density behavior of nuclear symmetry energy. The nuclear
radial flow, however, depends only weakly on the symmetry energy.
