Behavior and measurement of distributed sources in a shielding matrix using gamma spectroscopy
As part of its mission, the Department of Energy generates transuranic waste materials. Some of these wastes are present in large waste containers. The accurate assay of these waste materials in large containers poses unique challenges. These wastes have radioactive sources that are spread throughout the container with a variety of waste matrices that provide shielding. Although multiple well established and validated methods that use active and/or passive neutron detection in conjunction with gamma spectroscopy exist to assay these waste materials, these methods are expensive and not readily available at any given facility. As a result, less expensive alternatives, such as gamma spectroscopy alone, are often used. This paper researches the impact of a distributed shielding medium on a distributed transuranic source and the physical limitations of using gamma spectroscopy alone, without the benefit of either active or passive neutron counting. This included comparing the assay results from a gamma spectroscopy based system to one that uses passive neutron counting in addition to gamma spectroscopy. The differences between these systems were noted, and then evaluated through modeling using MCNPX to determine the cause of the observed discrepancies.
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