  The determination of the centrality of nuclear collision or the value of the
impact parameter of heavy nuclei is of great importance for the analysis of all
experimental data and comparison with theory. One method is to measure the
number of spectators using a hadron calorimeter located at a small angle to the
nuclear beam. It is shown that with an achievable resolution of the hadron
calorimeter in energy, the accuracy of determining the impact parameter is
insufficient for using the calorimeter in the MPD / NICA and CBM / FAIR
projects. The error reaches 35 % at a beam energy of 2.5 GeV even for
peripheral collisions. Secondary processes during the passage of spectators
through the nucleus give an additional contribution to the error for central
collisions and at medium centralities.
