Muons with E_th >= 1 Gev and Mass Composition in the Energy Range 10^{18}-10^{20} ev Observed by Yakutsk Eas Array

摘要

The ratio of the muon flux density to charged particle flux density atdistances of 300 and 600 m from the shower axis ($\rhom(300)/\rhos(300)$ and$\rhom(600)/\rhos(600)$) is measured. In addition, the energy dependence of$\rhom(1000)$ is analysed for showers with energies above $10^{18}$ eV. Acomparison between the experimental data and calculations performed with theQGSJET model is given for the cases of primary proton, iron nucleus and gamma-ray. We conclude that the showers with $\E\ge3\times10^{18}$ eV can be formedby light nuclei with a pronounced fraction of protons and helium nuclei. It isnot excluded however that a small part of showers with energies above $10^{19}$eV could be initiated by primary gamma-rays.