Pair Production

  The dominant interaction process for high-energy photons. Only at low energies (below 10 MeV) do Compton scattering and photoelectric absorption compete in cross-section.

For the calculation of electromagnetic showers, the energy spectrum of the generated positron (electron) can be approximated by [Lohrmann81]:

with

This formula holds for , and for k>10 MeV, where

The total probability for pair production over a path is given by

expressed more simply, the attenuation length due to pair production is 9/7 times the radiation length.