  Within a transport model we search for potential probes of the isospin
dependence of the in-medium nucleon-nucleon (NN) cross sections. Traditional
measures of the nuclear stopping power are found sensitive to the magnitude but
they are ambiguous for determining the isospin dependence of the in-medium NN
cross sections. It is shown that isospin tracers, such as the neutron/proton
ratio of free nucleons, at backward rapidities/angles in nuclear reactions
induced by radioactive beams in inverse kinematics is a sensitive probe of the
isospin dependence of the in-medium NN cross sections. At forward
rapidities/angles, on the other hand, they are more sensitive to the density
dependence of the symmetry energy. Measurements of the rapidity/angular
dependence of the isospin transport in nuclear reactions will enable a better
understanding of the isospin dependence of in-medium nuclear effective
interactions.
