For the transport calculation of gamma rays including bremsstrahlung, an improvement is made in the PALLAS-PL, SP discrete ordinates direct-integration code to enable evaluation of bremsstrahlung. The electrons resulting from Compton scattering, pair production, and the photoelectric effect are individually evaluated based on the primary gamma-ray flux calculated with the code. Bremsstrahlung production is then calculated by applying the continuous electron slowing down model. For this purpose, both the electron stopping power and the differential cross section for bremsstrahlung production are evaluated. Comparisons of PALLAS calculations with experiments are presented to test the validity of this code and method. As a result, it has been observed that the PALLAS calculations result in fairly good agreement with experiments, except for some discrepancies at energies below ∼0.7 MeV in the energy spectrum transmitted through lead and iron from a plane isotropic 6.2-MeV gamma-ray source. There is agreement also with another experiment on the attenuation by lead of transmission dose ∼8-MeV gamma rays in a normally incident from a plane monodirectional source. Further, there is agreement with the energy spectrum in lead calculated by a moments method for a plane monodirectional 8-MeV source without inclusion of secondary photons. Also presented are calculations of buildup factors and of energy spectra, including the contribution of bremsstrahlung, for a plane monodirectional beam of 8-MeV gamma rays normally incident on lead and on tungsten.
