  Considering the high-energy limit of the QCD gluon distribution inside a
nucleus, we calculate the proton-nucleus total inelastic cross section using a
simplified dipole model. We show that, if gluon saturation occurs in the
nuclear surface region, the total cross section of proton-nucleus collisions
increases more rapidly as a function of the incident energy compared to that of
a Glauber-type estimate. We discuss the implications of this with respect to
recent ultra-high-energy cosmic ray experiments.
