Formation of ions by high energy photons

We calculate the electron energy spectrum of ionization by a high energy photon, accompanied by creation of electron-positron pair. The total cross section of the process is also obtained. The asymptotics of the cross section does not depend on the photon energies. At the photon energies exceeding a certain value $\omega_0$ this appeares to to be the dominant mechanism of formation of the ions. The dependence of $\omega_0$ on the value of nuclear charge is obtained. Our results are consistent with experimental data.