  The ratio of the number of muons with a threshold of 1 GeV and charged
particles at a distance of 600 m from the axis is analyzed. Air showers with
energies above 5 EeV and zenith angles with less than 60 degrees are
considered. Comparison of experimental data with calculations by the
QGSJETII-04 model for various primary nuclei, including a gamma ray, showed
that the mass composition of cosmic rays up to energies of $\sim$ 10 EeV mainly
consists of protons and helium nuclei, with a small number of heavy nuclei.
Data include air showers with a very low muon content, which are assumed to be
produced by primary gamma rays.
