Experimental muon number distributions in Extensive Air Showers obtained at Moscow State University with enlarged statistics and improved procedure for muon number determination are analysed in the framework of an updated quark-gluon string model. The primary mass composition at energies before and after the kink in the primary energy spectrum is estimated. Mass composition before the kink is close to a normal one, and after the kink experimental data agree with the assumption that normal composition becomes enriched slowly by heavy nuclei according to the Peters-Zatsepin model.

The results of a calculation of the characteristics of the muon flux in thecomposition of extensive air showers are compared with the results ofexperiment. The quark-gluon string model was taken as the basicnuclear-interaction model at high energies. It is shown that the experimentaldata (energy spectrum and lateral distribution of muons) agree with the resultsof the calculation. In the framework of the model adopted for the nuclearinteraction, the experimental data on the nuclear composition of the primarycosmic radiation generating extensive air showers are discussed.

Muon energy spectra and muon lateral distribution in EAS were investigated with the underground magnetic spectrometer working as a part of the extensive air showers (EAS) array. For every registered muon the data on EAS are analyzed and the following EAS parameters are obtained, size N sub e, distance r from the shower axis to muon, age parameter s. The number of muons with energy over some threshold E associated to EAS of fixed parameters are measured, I sub reg. To obtain traditional characteristics, muon flux densities as a function of the distance r and muon energy E, muon lateral distribution and energy spectra are discussed for hadron-nucleus interaction model and composition of primary cosmic rays.