Photon Buildup Factors in Laminated Dual-Layer Shields

In radiation protection, photon buildup factors provide a convenient method for calculating dose and exposure response after various shielding configurations, as well as information about the behavior of radiation in these configurations. Though many situations call for multilayer shields, few databases and derived analytical formulas for photon buildup in multilayer shields exist. This research develops buildup factors and analytical fits to these data for slab-geometric, dual-layer shields composed of various materials. The photon buildup factors were calculated for monoenergetic photon sources incident on two-layer shields of various combinations of lead, polyethylene, aluminum, and stainless steel for thicknesses varying between 2 and 20 mean free paths using the Parallel Time Independent Sn (PARTISN) discrete ordinates code. The Gauss-Lobatto S₁₀₀ quadrature was used with a 244-energy-group structure and coupled photon and electron cross sections. Data from PARTISN calculations were then benchmarked for representative cases using MCNP5, and fits to a new analytical formula were developed using Mathematica 6.0.