Attenuation Correction Procedures

Nuclear materials subject to nondestructive assay (NDA) are often macroscopic objects composed of highly attenuating material. In some situations, the objects under assay are also obscured by containers or shielding. Gamma rays emitted within the item matrix are subject to collisions in the material matrix or other intervening materials before reaching the detector. The loss of photons that occurs in the material of the item is referred to as self-attenuation, and loss due to collisions in other intervening materials is external attenuation. These effects are key limiting factors for using gamma rays for the measurement of special nuclear material mass in extended sources. A description of and process for performing correction for external attenuation and self-attenuation is presented in this chapter.