  Within a Boltzmann transport model, we demonstrate correlation between
stopping observables and shear viscosity in central nuclear collisions at
intermediate energies (on the order of 10 to 1000 MeV/nucleon). The correlation
allows us to assess the viscosity of nuclear matter, by tuning the in-medium
nucleon-nucleon cross section in our transport model to agree with nuclear
stopping data. We also calculate the ratio of shear viscosity to entropy
density to determine how close the system is to the universal quantum lower
limit proposed in the context of ultrarelativistic heavy ion collisions.
