Constant efficiency selection of EAS with energies 105-107 GeV at observation level 700 g cm-2

A new EAS selection method is developed and applied for analysis of Tien Shan experimental data. It is shown that it is possible to select, at an observation level of 700 g cm-2, showers with energies 105-107 GeV with constant efficiency, i.e. not depending on the nature of the initiating primary particle. The proposed method tested on the basis of muon and electron EAS components gives the basis for a practically unbiased estimation of the mass composition and energy spectrum of the primary cosmic radiation in the energy interval 105-107 GeV using EAS experimental data obtained at mountain altitudes.