The total cross-sections for the photoeffect for 2S-subshell bound   electrons and pair production with the created electron in the 2S subshell   for photon energies above 1 MeV
  Considering the contributions of the main term of the relativistic Coulombian Green function given by Hostler [J. Math. Phys, 5, 591 (1964)] to the second order of the S-matrix element and taking into account only the large components of Dirac spinor of the 2S subshell, we have obtained the imaginary part of the Rayleigh amplitudes in terms of elementary functions. Thereby, simple and high accurate formulae for the total cross-sections for photoeffect and pair production with the electron created in the 2S subshell are obtained via the optical theorem. Comparing the predictions given by our formulae with the full relativistic numerical calculations of Kissel et al [Phys. Rev. A 22, 1970 (1980)] and Scofield [LLRL, Internal Report (1973)], a good agreement is found for low and intermediate Z values if screening effects are taken into account, for photon energies above the pair production threshold energy. We present our numerical results for the total photoeffect and pair production cross-sections for the 2S subshell of Zn and Ag atoms, for various photon energies. 
A. Costescu, S. Spanulescu, C. Stoica