Monte Carlo approach to the detectability of a gamma source within a scrap-iron truckload

Although the use and disposal of radioactive materials are regulated by appropriate national and international agencies, the possibility that such materials could enter the recycling process as scrap cannot be overlooked. Several incidents in recent years have demonstrated that given the many varied uses of radioactive materials in modern industry and medicine, it is possible for these materials to find a way into a scrap processor's plant, where recycling may lead to internationally widespread contamination. This is a real problem that cannot be ignored. To the authors' knowledge, this problem has been tackled primarily on an experimental basis. A Monte Carlo approach to the modeling of a detection system for scrap-iron-loaded trucks is presented. The crucial point is the representation of system inhomogeneities, which inevitably introduces elements of uncertainty and subjectivity. Correspondingly, the results obtained, while physically reasonable, are such that their substance resides in the general behavior of the curves and in the orders of magnitude. To estimate detectability limits for real situations, both homogeneous and inhomogeneous loads are considered for various positions of shielded and unshielded gamma sources. A sensitivity analysis of the assumptions of the model has shown satisfactory results