Mass composition of cosmic rays above 0.1 EeV by the Yakutsk array data

Abstract

The paper presents the results of the longitudinal development of extensive air showers (Xmax) of ultra-high energies and mass composition of cosmic rays. The measurements of Xmax are based on data from observations of the Cherenkov radiation at the Yakutsk array for the period 1974–2014. The cascade curves of individual showers and the depth of maximum Xmax were reconstructed over the energy range 1016–5.7 · 1019 eV. It is shown that the displacement rate of the parameter dXmax/dE in the atmosphere is nonlinear and depends on the energy. Such a feature indicates a change in mass composition, which is confirmed by fluctuations of Xmax in this energy region. The composition of cosmic rays was determined by interpolation using the QGSJetII-04 model.