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.
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