Data on muon and electron components of extensive air showers (EAS) (obtained with the EAS MSU array) were used to derive the primary cosmic ray (PCR) mass composition. It is shown that for energies beyond the knee at energy $3\cdot10^{15}$ eV the abundance of heavy nuclei increases with energy. But at energies above $10^{17}$ eV the abundance of light nuclei starts to grow. The primary cosmic ray spectrum in the range 10$^{15}$-10$^{18}$ eV is analyzed. It is shown that at energies above $10^{17}$ eV the additional component appears and it differs from the bulk of Galactic cosmic rays generated by shocks in SN remnants.
96.50.sd Extensive air showers
D.V. Skobeltsyn Nuclear Physics Institute, Department of Super-High Energy Particles, M.V. Lomonosov Moscow State University, Leninskiye Gory 1, korp. 2, Moscow, 119991, Russia
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