Analysis of gamma-ray families with halos and estimation of mass composition of primary cosmic radiation at energies 1-100Â PeV

Characteristics of  γ-ray families with halos observed with X-ray emulsion chambers at the Pamirs and data of EAS experiments are analyzed to estimate the summary fraction of proton and helium nuclei (p + He) in the primary cosmic radiation (PCR) at E0 = 1-100 PeV. It is shown that the p + He fraction at E0 = 10 PeV is (39 ± 6) %. The mass composition, estimated by EAS age, remains mixed at E0 = 1-100 PeV with a tendency to become heavier with increasing energy.