Experimental results are presented on high energy cosmic-ray hadron interactions recorded in homogeneous-type thick lead chambers (total thickness being 60 cm and 110 cm) exposed at the Pamirs (atmospheric depth 595 g/ cm2). High energy cosmic-ray hadron flux is measured. The attenuation mean free path of the arriving cosmic-ray hadrons of Ehγ ≥ 6 TeV measured in the chamber is obtained as 252 ± 30 g/cm2 of lead. However, for the high energy hadrons (E(γ) ≥ 10 TeV) constituting cosmic-ray families of the highest energy range, ΣE(γ) ≥ 700 TeV, which have been accumulated so far in the series exposures at the Pamirs and analysed by MSU group, the attenuation mean free path of hadrons in lead has turned out to be as short as 170-26+47 g/cm2 with 95% CL by the maximum likelihood method. The present experimental result of such a short attenuation length of hadrons in cosmic-ray families is essentially consistent with that obtained for high energy hadrons (E(γ) ≥ 10 TeV) constituting the "Chiron-type" families of ΣE(γ)>100 TeV in the Chacaltaya two-storeyed chamber experiments. The anomalous transition characteristics of high energy hadrons in lead is found and examples are presented. The physical significance of the experimental results on extremely high energy hadron interactions is discussed.
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