Photon and electron data bases and their use in radiation transport calculations

Traditionally, the data included in the ENDF/B photon interaction data base have been sufficient to describe the interaction of primary photons with matter. The data usually contained in this data base included: (1) cross sections: coherent and incoherent scattering, pair production as well as photoelectric absorption; and (2) form factors and scattering functions: to describe the angular distribution of coherent and incoherently scattered photons. These data were sufficient to describe the interaction of primary photons with matter. However, they were not adequate to uniquely define the emission of secondary photons following photoelectric effects such as fluorescence. Traditionally, it has been assumed that when a photoelectric event occurs, all of the energy of the incident photons is deposited at the point of the interaction. In fact, in the case of photons with energies near the K photoelectric edge of lead, almost 88% of the energy will be reradiated as fluorescence X rays. Traditional data also did not include the effect of anomalous scattering on coherent scattering. Including this effect predicts a coherent scattering cross section that approaches zero at low energy, as opposed to the constant low-energy limit predicted by simply using form factors. Lastly, traditional data did not differentiate betweenmore » pair and triplet production.« less