9 research outputs found
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An innovative method for extracting isotopic information from low-resolution gamma spectra
A method is described for the extraction of isotopic information from attenuated gamma ray spectra using the gross-count material basis set (GC-MBS) model. This method solves for the isotopic composition of an unknown mixture of isotopes attenuated through an absorber of unknown material. For binary isotopic combinations the problem is nonlinear in only one variable and is easily solved using standard line optimization techniques. Results are presented for NaI spectrum analyses of various binary combinations of enriched uranium, depleted uranium, low burnup Pu, {sup 137}Cs, and {sup 133}Ba attenuated through a suite of absorbers ranging in Z from polyethylene through lead. The GC-MBS method results are compared to those computed using ordinary response function fitting and with a simple net peak area method. The GC-MBS method was found to be significantly more accurate than the other methods over the range of absorbers and isotopic blends studied
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A demonstration of the gross count tomographic gamma scanner (GC-TGS) method for the nondestructive assay of transuranic waste
The authors examined the accuracy and sensitivity levels for three variations on the TGS method: the original TGS method using a high-purity germanium (HPGe) detector to measure net areas of full-energy gamma-ray peaks; a modified HPGe-detector method that uses net areas for the transmission analysis and the gross count TGS (GC-TGS) method for the emission analysis; and a NaI-detector method that uses the GC-TGS method exclusively. They found that while the accuracies of the methods were comparable, the GC-TGS method boosted the sensitivity per detector by a factor of approximately two for the HPGe GC variation and four for the NaI method. The implications for improved TGS scanner design are discussed
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Estimation of obliquely scattered gamma-ray response functions in the gross-count tomographic gamma scanner (GC-TGS) Method
The gross-count tomographic gamma scanner (GC-TGS) method for assaying transuranic waste in 208-1 drums is being developed to allow NaI and other low-resolution gamma-ray detectors to be used in place of high-purity germanium (HPGe) detectors in TGS systems. It was recently shown that a logarithmic response-function technique based on the material basis set (MBS) formalism used in the TGS method allows gross spectra from NaI detectors to be used in both measuring MBS transmission corrections using external transmission sources and in applying the corrections to emission spectra to arrive at radionuclide mass estimates. In this work the authors have attempted to show that addition of the oblique scatter component can increase the accuracy of the GC-TGS measurements with both NaI and high-purity germanium detectors. This paper describes the formalism behind the GC-TGS method and the improvement achieved in the analysis by including the scatter component
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Alpha contamination assessment for D&D activities: Monitoring concrete surfaces
The process of decontaminating and decomissioning former nuclear facilities sometimes requires that large areas of concrete and other materials be scanned to verify they are not contaminated. A specially developed concrete surface monitor (CSM) can greatly expedite that process. The CSM is basically an aluminum box, open on the bottom, that uses an electrostatic field to transport ions created by alpha particles interacting with ambient air to a collection grid or plate. A sensitive electrometer measures the resulting current, which is essentially proportional to surface alpha activity. The initial prototype CSM surveys a surface area of some 300 cm{sup 2} at one time, while a second-generation prototype surveys 2500 cm{sup 2} and is designed to compensate automatically for radon, which can cause substantial errors in estimating surface contamination in some cases. These monitors have been successfully demonstrated on a number of concrete surfaces in situ as well as on concrete pieces cut from former facilities
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Alpha contamination assessment for D&D activities: Technology overview
Instruments based on the principle of Long-Range Alpha Detection (LRAD) detect the ions created in ambient air by Ionizing radiation, particularly alpha radiation, interacting with air molecules. Using either an electrostatic field or forced convection, these ions can be transported to a detection grid where the ions produce a small current that is measured with a sensitive electrometer. LRAD-based instruments can give separate, simultaneous measurements of alpha-emitting solids and inert radioactive gases such as radon. LRAD-based instruments assess surface contamination on an entire object or large surface area in a single, rapid measurement, including relatively inaccessible areas such as interior surfaces of pipes and process equipment. The LRAD concept is well proven and has been developed into a range of different radiation detection devices. This paper presents an overview of the technology, while several associated papers explore specific applications in greater detail
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Alpha contamination assessment for D&D activities: Monitoring pipe interiors
We have developed a prototype instrument capable of assessing alpha-emitting contamination on interior surfaces of ducts, pipes, tanks, and other enclosed volumes without inserting a probe. Air is drawn through the potentially contaminated volume and then through a detection grid, where ions created in the air by alpha particles are collected and the resulting charge measured with a sensitive electrometer. A filter at the intake end of the contaminated volume excludes externally created ions, so only ions generated inside the volume are detected. We have studied the response of this prototype in initial experiments using calibrated alpha sources with various pipe diameters and configurations, air flows, and source locations in the pipes. The results of these experiments indicate that this method can be an effective approach to assessing internal contamination
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Alpha characterization of concrete surfaces at Decontamination & Decommissioning (D&D) sites
Waste minimization and worker protection at D&D sites requires continual and extensive characterization for radioactive contamination. Contamination detectors that are sensitive, rugged, fast, and capable of covering large areas are needed. The concrete surface monitor (CSM) developed at LANL supports both characterization and waste minimization efforts at D&D sites containing large concrete surfaces and structures of different forms and shapes. This report describes the CSM design and the results of several field experiments