Calculated and measured dose buildup factors for gamma rays penetrating multilayered slabs

Dose buildup factors for normally incident 662-keV gamma rays penetrating multilayered aluminum-lead slabs were measured for various combinations using thermoluminescence dosimeters. The results were compared with calculated values obtained from a gamma-ray transport code and with values inferred from a semiempirical formula using single-layer slab buildup factors. This formula, a slightly modified version of the Kalos formula, predicts buildup factors in excellent agreement with both experiments and calculations, even for multilayered combinations. The formula also provides buildup factors which are in good agreement with transport calculations for other source energies and slab materials, indicating a probable wide range of validity.