Fraction of energy, E em /E 0 , transferred to the electron-photon component of EAS at E 0 = 10 15 ± 10 19 eV was estimated by using the Cherenkov radiation data and the data on charged particles obtained at the Yakutsk EAS array. The results are compared with predictions of different models for energy dissipation into the EAS electron-photon component and with calculations performed with different primary nuclei content. In the energy ranges 10 15 ± 10 16 eV and 10 18 ± 10 19 eV , the ratio E em /E 0 is equal to (77 ± 2)% and (88 ± 2)%, respectively, that does not contradict to a mixed composition of primary particles in the first energy interval and purely proton composition in the second one.

The energy spectrum of ultra-high energy cosmic rays (UHECRs) is discussed on the basis of the Yakutsk array database analysis. In the region E-0 = 10(17) to 3 x 10(19) eV the showers are detected under trigger-500, while at energies above 3 x 1019 eV the whole acceptance area for trigger-1000 is used in order to utilize all the data available in the region of Greisen-Zatsepin-Kuzmin (GZK) cutoff. Updated relations are adapted to estimate the primary energy having detected densities of charged particles at the distance 300/600 m from the shower axis.

The Yakutsk array observes the Cherenkov light emitted by UHECR in atmosphere. Recently, an autonomous subarray has been added consisting of photomultipliers to measure the showers in the knee region. Our aim is to analyze the combined data set in order to derive the cosmic ray spectrum in an energy range as wide as possible using the same technique.The advantage of the air Cherenkov light measurement is the model independent estimation of the EAS primary energy using the total light flux emitted in the atmosphere. A set of the light lateral distributions observed in the extended energy range is presented.

Data for the electron-photon, the muon and Cerenkov components of EAS, registered with the Yakutsk array during long data collection periods, are presented. The data appear of specific interest as control samples for the development of advanced hadronic interaction models and for checks of differences of various types of models (scaling procedures - QCD inspired models). Preliminary results of the analysis exhibit a satisfactory description of the experimental observations above 10(18) eV by scaling violation, and they require slightly larger multiplicities of the secondary particle production in the energy range of 50 - 500 PeV. The results appear also to be in agreement with a mixed composition in this energy range, approximately like that known for primaries of 10(12) eV. This conclusion is also consistant with the frequency of muons (greater than or equal to 1 GeV), observed at 300 m distance from the core of 50 - 500 PeV EAS.

Experimental data on muons (with threshold energy of 1 GeV) in extensive air showers (EAS) obtained at the Yakutsk EAS array from 1974 to 1992 are presented. Periods of reliable detector operation have been selected. Muon detector readings near the threshold have been carefully taken into account. Mean lateral distribution functions (LDF) of muons in the energy range of 1017–5 × 1019 eV and the zenith angle range of 0–60 ° have been obtained. The dependence of LDF on E0 and θ at energies above 5 × 1018 eV is shown to be considerably different in comparison with the region of lower energies.

This is a presentation of Yakutsk data of primary cosmic ray energy spectrum above 10(17) eV. The differential energy spectrum has a complicated form. Near E(a) = 10(18.95) eV a dip is formed (statistically significant is 7.9 sigma). In this energy region the analysis results of a shower arrival direction distribution in the galactic latitude were dealt with also.

The extensive air showers spectrum on scintillation desity Rko in primary energy region E sub approx. 10 to the 15th power - 10 to the 20th power eV on the Yakutsk array data and recent results of the Akeno is given.