  It is well known that intranuclear-cascade models generally overestimate the
cross sections for one-proton removal from heavy, stable nuclei by a
high-energy proton beam, but they yield reasonable predictions for one-neutron
removal from the same nuclei and for one-nucleon removal from light targets. We
use simple shell-model calculations to investigate the reasons of this
deficiency. We find that a correct description of the neutron skin and of the
energy density in the nuclear surface is crucial for the aforementioned
observables. Neither ingredient is sufficient if taken separately.
