Irregularity in the Primary Cosmic Rays Mass Composition at an Energy of ~10 PeV

Irregularity in the mass composition of primary cosmic rays (PCR) at an energy of ∼10 PeV is reviewed. To assess changes of the PCR mass composition, the X-ray emulsion chamber (XREC) method and the halo-method based on XREC were used. The study of changes in the PCR mass composition was carried out based on experimentally obtained characteristics of the extensive air shower (EAS) trunks, where fluctuations of these characteristics are minimal and information about the primary interaction of PCR nuclei with atmospheric atoms is maximally preserved. It is shown that at an E₀ = 10 PeV there is a local maximum of the heavy nuclei fraction. This maximum is correlated with the PCR sources including stars of variable SR (red giants and super-giants) and WR (Wolf-Rayet) types.