Formulas Giving Buildup Factor for Double-Layered Shields

Formulas that give absorbed dose buildup factors for two-layered shields have been developed based on gamma-ray absorption buildup factors computed with the Monte Carlo Neutral Particle Transport Code System (MCNP). The shielding materials considered were water, lead, steel, concrete, and some of their combinations for two-layered shields with thicknesses between 1 to 10 mfp. Gamma energy considered ranged from 0.5 to 6 MeV. The formulas reproduce MCNP results with a difference of <10%, in most cases <3%.