  We confirm the result obtained many years ago at Tien-Shan mountain station
with the large 36-m2 lead calorimeter that in extensive air showers (EAS) with
energies of few PeV the attenuation of core energy deposit in lead becomes
slower than it could be predicted by modern codes. It is shown that this effect
is connected with the appearance of the excess of abnormal cores with a large
ionisation released in lower layers of the calorimeter and these abnormal EAS
cores are most probably produced by high-energy muon groups. A few hypotheses
of the excess of muon reach EAS cores are considered. To study the absorption
of EAS hadrons and muons in a lead ionization calorimeter, the EAS development
in the atmosphere was simulated in the framework of the CORSIKA+QGSJET code
whereupon the passage of hadrons and muons through a lead calorimeter has been
modeled with using the FLUKA transport code.
