Precision estimates for tomographic nondestructive assay Page: 3 of 6
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PRECISION ESTIMATES FOR TOMOGRAPHIC NONDESTRUCTIVE ASSAY
T. H. Prettyman
Los Alamos National Laboratory
Los Alamos, New Mexico, 87544
Requirements for effective safeguards during the transition to environmental
management at nuclear material production facilities within the DOE complex are deriving
improvements in the accuracy of nondestructive assay (NDA) techniques. An important
aspect of the transition is the need for facilities to terminate safeguards on waste materials,
thus reducing the cost for safeguards at the facility. Requirements for the termination of
safeguards on candidate waste material have been established by DOE to minimize the
potential for diversion or theft of nuclear material. Because heterogenous waste and
residue materials are stored in large containers such as 208-L drums, conventional assay
techniques such as segmented gamma scanning (SGS) that were developed to assay small
samples cannot always provide accurate measurements. Consequently, facilities using the
conventional NDA instrumentation may be limited in their ability to discard waste materials
in compliance with DOE requirements.
One technique being applied to improve the accuracy of assays of waste in large
containers is computerized tomography (CT). Research on the application of CT to
improve both neutron and gamma-ray assays of waste is being carried out at Los Alamos
National Laboratory."2 For example, tomographic gamma scanning (TGS) is a single-
photon emission CT technique that corrects for attenuation of gamma rays emitted from the
sample using attenuation images from transmission CT." By accounting for the
distribution of emitting material and correcting for attenuation of the emitted gamma rays,
TGS is able to achieve highly accurate assays of radionuclides in medium-density waste.
The spatial resolution used in TGS (-2 in.) was selected to minimize bias while satisfying
common facility throughput requirements (>8 drums per 8-hour shift).1
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Prettyman, T.H. Precision estimates for tomographic nondestructive assay, article, February 1, 1995; New Mexico. (digital.library.unt.edu/ark:/67531/metadc717228/m1/3/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.