Purely Angular Effects of Photon Buildup Factors for Thin Shields of Lead, Iron, Aluminum, and Water

This study investigates purely angular effects on photon buildup factors for slabs with optical thickness up to 10 mean free paths. Photon buildup factors are determined for different slabs, upon which monoenergetic photons between 50 keV and 10 MeV are incident at angles between 0 and 1.48 radians. As the incident angle is increased, the physical slab thickness is reduced to maintain a constant slant-path optical thickness relative to incident photons. This method identifies previously unexplored angular relationships between slab thickness and incident angle. Coupled electron/photon cross sections are used to account for secondary photon effects of bremsstrahlung and electron binding energies. The discrete ordinates code PARTISN is used to determine angular photon buildup factors for ten incident energies and ten incident angles for lead, iron, aluminum, and water slabs. Portions of these results are applicable to other slab geometry buildup studies.