Determination of transmission factors for photons in multilayered shieldings using 4 materials: comparison between analytical formulae and computational modeling

The aim of this paper is to determine the Transmission Factors (TF) for photons in multilayered shieldings using 4 different materials, through analytical calculation methods and computational modeling. The thicknesses and materials considered are as follows: 0,5 cm of ordinary concrete, 0,5 cm of aluminum, 0,5 cm of iron and 0,5 cm of lead. The layers were permuted in 24 different sequential arrangements. It was considered an isotropic point source emitting monoenergetic photons of energy 0.661657 MeV for interactions with matter. Analytically, the exponential attenuation and Taylor's buildup factors (TB) were calculated for infinite medium, it was also used the Broder's Equation (BE) and then, Microsoft Excel to calculate the TF for different arrangements. In the computational modeling, the Monte Carlo N-Particle code (MCNP), based on the Monte Carlo Method (MCM), was used. MCNP simulations were performed to obtain dose values with and without the use of shielding arrangements, respectively, I and I₀. The ratio I/I₀ is termed as TF. The TF of the 24 possible permutations has shown good agreement between the analytical methodology and MCNP simulations. Simulated TF presents a slightly higher value in each combination. Regarding dose attenuation, the most appropriate order of materials in the source-detector direction is as follows: ordinary concrete, aluminum, iron and lead. (author)