Theoretical Dose Transmission and Reflection Probabilities for 0.2-10.0 MeV Photons Obliquely Incident on Finite Concrete Barriers

Berger et al. of the National Bureau of Standards have utilized the Monte Carlo method to calculate total scatter differential dose transmission and reflection coefficients for plane unidirectional gamma rays incident on concrete barriers of finite thickness. These calculations were performed for source energies of 0.2, 0.4, 0.66, 1.25, 5.0, and 10.0 MeV with incident obliquity angles cos θ₀ = 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01; emergent obliquity angles cos θ_d = 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01; emergent azimuthal angles relative to the ongoing incident ray = 0, 30, 60, 90, 120, 150, and 180 degrees; and slab thicknesses of 0.25, 0.5, 0.75, 1, 2, 3, and 4 mean-free-paths. These data are used herein to compute dose rate slant penetration and reflection probabilities for a detector located adjacent to a barrier. The total scatter contribution was calculated by numerically integrating the Monte Carlo data of Berger et al. over the 2π solid angle subtended by the barrier relative to the detector location. In addition to results for the above listed thicknesses, energies, and incident obliquities, slant penetration and reflection probabilities are computed for the 1.12 h unfractionated fission spectrum by interpolating and weighting the Monte Carlo data at appropriate energies and thicknesses. The probabilities obtained herein compare favorably with those obtained by the Spencer-Fano moments method for an infinite medium, with other Monte Carlo studies, and with experimental data.