Cross sections of interaction of ultrarelativistic hydrogen and positronium atoms with hydrogen, carbon, nitrogen, and argon atoms

The cross sections of interaction of hydrogen and positronium atoms with hydrogen, carbon, nitrogen, and argon atoms are calculated in the first Born approximation. The C, N, and Ar atoms are described using atomic form factors and incoherent-scattering functions obtained in the Hartree--Fock method. The calculated cross sections for ionization of hydrogen are compared with previously published theoretical cross sections and experimental cross sections obtained at low energy. The comparison shows that the uncertainty in the theoretical ionization cross sections for hydrogen does not exceed ±10%. The calculated total cross section of interaction of positronium with carbon is compared with the experimental cross section in the interval of γ factors 800--2000