High energy gamma-families with halo and mass composition of primary cosmic rays in energy region above 10 PeV

The experimental spectrum of halo areas for gamma-families with SigmaE(gamm a) greater than or equal to 500 TeV is obtained and compared with simulatio ns in quark-gluon string model. The comparison suggests a similar to 2 time s decrease of the proton fraction in primary cosmic ray (PCR) composition i n the energy region 10(16) divided by 10(17) eV. However at an energy above 1017 eV, the experimental flux of halo events with area exceeding 300 divi ded by 400 mm(2) is 5 divided by 10 times larger than the simulated one. Su ch a difference may be explained by the assumption that in this region the fraction of protons increases as much as 3 times, while the slope of the sp ectrum decreases (gamma = 2.6 divided by 2.7).