Estimate of the Mass Composition of Ultrahigh Energy Cosmic Rays
  It is proposed a new approach for estimating the composition of cosmic rays. It is found that the zenith angle distributions and muon components of EAS for energies E>10^19 eV and E>4.10^19 eV differ from each other. It is shown that the cosmic rays above E>4.10^19 eV is heavier than the cosmic rays at energy E~ 10^19 eV. According to our estimation the SUGAR array detected 8 showers above 10^20 eV. It is concluded that no sign of Greisen-Zatsepin-Kuzmin (GZK) cut off in the spectrum of cosmic rays and all cosmic rays are galactic. 
A.A. Mikhailov, N.N. Efremov, N.S. Gerasimova, I.T. Makarov, G.V.   Nikolayeva, G.G. Struchkov