gamma-Families with Halos Observed by X-ray Emulsion Chamber in EAS and the Estimate of the p+He Fraction in Primary Cosmic Rays at E0 = 1-100 PeV

The experimental gamma-families in which events called "halos" were detected using X-ray emulsion chambers (XRECs) of the PAMIR experiment are described. The halo nature is explained within the standard model of nuclear interactions. Based on events with halo, the fraction of p+He in primary cosmic rays (PCR) was estimated. It is shown that the PCR mass composition remains mixed in the range E0 = 1-100 PeV.