  The concept of centrality in high-energy nuclear collisions has recently
become a subject of an active debate. In particular, the experimental methods
to determine the centrality that have given reasonable results for many
observables in high-energy lead-lead collisions at the LHC have led to
surprising behaviour in the case of proton-lead collisions. In this letter, we
discuss the possibility to calibrate the experimental determination of
centrality by asymmetries caused by mutually different spatial distributions of
protons and neutrons inside the nuclei --- a well-known phenomenon in nuclear
physics known as the neutron-skin effect.
