Dose buildup factor formula for double-layered shields

In radiation shielding, health physics, and radioactive waste management, it is very important to know buildup factors for various materials and their combinations used as multilayer shields. In this work, a general formula that computes buildup factors for double-layer shields was developed on the basis of Monte Carlo photon transport using the MCNP code. Formulas for buildup factors for double-layer shields have been developed in the past with various degrees of success and limitations. The GP formula is excellent but applies to single-layer materials only. In this work, gamma-ray dose buildup factors for double-layer shields have been computed using the MCNP code. A point monoenergetic isotropic source was used with energy from 0.5 to 6 MeV. The source was placed at the center of the first spherical materials, surrounded by a second one. Detectors were placed on the surface of the second material and used to tally the photon flux in a six-energy-group structure. The shielding materials considered were water, lead, steel, concrete, and some of their combinations for double-layered shields ranging in thickness from 1 to 10 mean free paths (mfp)