Mass composition of primary cosmic rays at energies 1014-3×1015eV

The flux of hadrons at energies around 10 13 -10 14 eV measured by the Mount Fuji experiment has been compared with fluxes predicted for different assumptions about the mass composition of primary cosmic rays. It is shown that agreement between experimental data and prediction can be obtained only if the average mass of the primaries does not increase significantly up to a few times 10 15 eV. It is concluded that the changes in the picture of cosmic-ray propagation, considered by some authors as due to enrichment of the primary flux by heavy-mass nuclei, have to be interpreted rather in terms of the interaction properties of high-energy hadrons.