  The experimental results on the behaviour of the characteristics of secondary
particles depending on the disintegration degree of nuclei are used to
determine the region of central collisions. It was therefore possible that : -
the correlation between the prosesses of total disintegration of nuclei and the
central collisions of nuclei had been shown; - the existence of the regime
change points in the behaviour of the considered characteristics of secondary
particles depending on the disintegration degree of nuclei had been observed in
the other earlier experiments as well. The number of all protons in
12CC-interactions at the momentum of 4.2 A GeV/c obtained from the 2-m propane
bubble chamber exposed at the Dubna machine is considered as a disintegration
degree of nuclei. The experimental results demonstrate that there are cases
corresponding to the critical phenomena among the events with the central
collisions of nuclei. For 12CC-interaction the behaviour of the number of the
events, depending on Q also depends on the number of fragments and has a
two-steps form. This result could be explained by the existence of nuclear
clusters. The experimental results on the relation between the number of
events, the angular distributions of protons and full number of protons are
presented for 12CC-interactions at the momentum of 4.2 A GeV/c. The influence
of nuclear fragmentation process on the results is also considered. The
obtained results confirm the assumption that there exist the critical phenomena
among the central collisions and it is necessary to use a percolation approach
for the full description of the central collisions.
