Calculation of buildup factors for multilayer slab shields using the Monte Carlo method

Gamma-ray beams normally incident upon slab shields of varying compositions are studied using a computer program based upon the Monte Carlo technique. Initial gamma energies of 1, 4, 6, and 8 MeV are considered. The shielding materials used were aluminum, iron, and lead. Both single and double material shields were investigated, at a variety of thicknesses up to a maximum of five mean free paths. Two secondary gamma processes are included in this simulation: annihilation gammas from pair production and bremsstrahlung from the electrons. The primary effort is the calculation of the dose, energy, and number buildup factors for these shields. The results for a single material agree quite well with experimental values, and the double material results agree with previous calculations. Secondary results obtained include the pattern of energy deposition within the shield and the variation in beam energy and radial spectra as it passes through the shield. The most important conclusion resulting from this work is that secondary gammas must be considered to obtain valid results when studying heavy materials at incident gamma energies greater than 1 MeV --Abstract, page ii