  We study medium modifications of the nucleon-nucleon (NN) cross sections and
their influence on the nucleon knockout reactions. Using the eikonal
approximation, we compare the results obtained with free NN cross sections with
those obtained with a purely geometrical treatment of Pauli-blocking and with
NN obtained with more elaborated Dirac-Bruecker methods. The medium effects are
parametrized in terms of the baryon density. We focus on symmetric nuclear
matter, although the geometrical Pauli-blocking allows for the treatment of
asymmetric nuclear matter. It is shown that medium effects can change the
nucleon knockout cross sections and momentum distributions up to 10% in the
energy range E=50-300 MeV/nucleon. The effect is more evident in reactions
involving halo nuclei.
