Bremsstrahlung account in photon transport

Abstract

This chapter proposes a new thick-target bremsstrahlung model including angular and spatial distributions (TTBIAS) model to account the bremsstrahlung in photon transport calculations in “thick” domains. This model assumes local absorption of electrons and positrons at the generation point and the emission of all resulting bremsstrahlung photons. The number of bremsstrahlung photons and spectral, angular, and spatial energy distribution of those bremsstrahlung photons per single interaction act of the primary photon is precalculated and tabulated. To increase the computational accuracy, a model accounting the spatial distribution of annihilation photon generation points was added to TTBIAS. In this model the spatial distribution of annihilation photon generation points is precalculated in cylindrical coordinates with ELISA code and tabulated like the spatial distribution of bremsstrahlung photon generation points in TTBIAS model. A lead layer example showed that TTBIAS values for photon outcome from thick layers agree well with those computed using the electron and positron transport scheme.