Mass composition of cosmic rays with energies $E_0 \geq 10^{17}$ eV according to the data from the ground-based detectors of the Yakutsk EAS array

The lateral distribution of charged particles measured by ground-based scintillation detectors in extensive air showers (EASs) with the energy $E_0\geq10^{17}$ eV at the Yakutsk EAS array in 1977–2013 has been analyzed. The experimental data have been compared to the calculations within various models of the development of EASs from the CORSIKA package. The experimental data are in the best agreement with the QGSJET-01-d and QGSJET II-04 models. The mass composition of cosmic rays in the energy range $(1{-}20)\cdot10^{17}$ eV changes from $\langle\ln A\rangle$ to a purely proton composition.