The incoherent (Compton) scattering cross sections in Ref.  were obtained from a combination of the Klein-Nishina formula and nonrelativistic Hartree-Fock incoherent scattering functions. Radiative and double Compton-scattering corrections were also included. The coherent (Rayleigh) scattering cross sections in Ref.  were calculated from a combination of the Thompson formula and relativistic Hartree-Fock atomic form factors. The photoelectric cross sections were obtained by Scofield  by a phase-shift calculation for a central potential and a Hartree-Slater atomic model. Scofield's results extend only up to 1.5 MeV. At higher energies, where the photoelectric cross section is quite small, a semi-empirical formula from Ref.  connects Scofield's values at 1.5 MeV to the asymptotic high-energy limit calculated by Pratt . Cross sections for pair production given in Ref.  are based on complicated combinations of formulas from Bethe-Heitler theory with various other theoretical models to take into account screening, Coulomb, and radiative corrections. Different combinations were used in the near-threshold, intermediate and high-energy regions to obtain the best possible agreement with experimental cross sections.
For elements with atomic numbers from 2 to 54, Scofield  presented correction factors for individual atomic subshells, with which the photo-effect cross sections can be renormalized so that they correspond approximately to a relativistic Hartree-Fock model rather than the Hartree-Slater model used in the original calculation. This renormalization is most significant for the outer atomic shells; the total cross section is lowered by no more than 10 percent at energies above 1 keV. Scofield did not actually apply the renormalization to the cross sections given in his tables. The renormalization was used, however, in the tabulations in Refs. [6,8,11]. Recent reviews [16,17] indicate that, on the whole, agreement with experiment is better when the renormalization is not done. We have therefore omitted the renormalization in the database for the XCOM program.