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Title: Performance Evaluation of Spectroscopic Detectors for LEU Hold-up Measurements

Abstract

The hold-up measurement of low-enriched uranium materials may require use of alternate detector types relative to the measurement of highly enriched uranium. This is in part due to the difference in process scale (i.e., the components are generally larger for low-enriched uranium systems), but also because the characteristic gamma-ray lines from 235U used for assay of highly enriched uranium will be present at a much reduced intensity (on a per gram of uranium basis) at lower enrichments. Researchers at Oak Ridge National Laboratory examined the performance of several standard detector types, e.g., NaI(Tl), LaBr3(Ce), and HPGe, to select a suitable candidate for measuring and quantifying low-enriched uranium hold-up in process pipes and equipment at the Portsmouth gaseous diffusion plant. Detector characteristics, such as energy resolution (full width at half maximum) and net peak count rates at gamma ray energies spanning a range of 60–1332 keV, were measured for the above-mentioned detector types using the same sources and in the same geometry. Uranium enrichment standards (Certified Reference Material no. 969 and Certified Reference Material no. 146) were measured using each of the detector candidates in the same geometry. The net count rates recorded by each detector at 186 keV and 1,001more » keV were plotted as a function of enrichment (atom percentage). Background measurements were made in unshielded and shielded configurations under both ambient and elevated conditions of 238U activity. The highly enriched uranium hold-up measurement campaign at the Portsmouth plant was performed on process equipment that had been cleaned out. Therefore, in most cases, the thickness of the uranium deposits was less than the “infinite thickness” for the 186 keV gamma rays to be completely self-attenuated. Because of this, in addition to measuring the 186 keV gamma, the 1,001 keV gamma ray from 234mPa—a daughter of 238U in secular equilibrium with its parent—will also need to be measured. Based on the performance criteria of detection efficiency, energy resolution, peak-to-continuum ratios, minimum detectable limits, and the weight of the shielded probe, a shielded (0.5 in. thick lead shield) 2 × 2 in. NaI(Tl) detector is recommended for use. The recommended approach is to carry out analysis using data from both 186 keV and 1,001 keV gamma rays, and select a best result based on propagated uncertainty estimates. It is also highly recommended that a two-point gain stabilization scheme based on an 241Am seed embedded in the probe be implemented. Shielding configurations to reduce the impact of background interference on the measurement of 1,001 keV gamma-ray are discussed.« less

Authors:
 [1];  [1];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division
Sponsoring Org.:
USDOE
OSTI Identifier:
1335357
Report Number(s):
ORNL/TM-2016/649
TRN: US1700828
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; SLIGHTLY ENRICHED URANIUM; GAMMA RADIATION; PORTSMOUTH GASEOUS DIFFUSION PLANT; KEV RANGE 100-1000; MEV RANGE 01-10; NAI DETECTORS; HIGH-PURITY GE DETECTORS; URANIUM 238; PROTACTINIUM 234; ENERGY RESOLUTION; PERFORMANCE TESTING; THICKNESS; LEAD; COUNTING RATES; ENRICHMENT; EVALUATION; GAIN; PEAKS; PIPES; PROBES; STANDARDS; EFFICIENCY; INTERFERENCE; SHIELDS; SEMICONDUCTOR DETECTORS; LANTHANUM BROMIDES; Low Enriched Uranium; Gamma Ray Holdup

Citation Formats

Venkataraman, Ramkumar, Nutter, Greg, and McElroy, Robert Dennis. Performance Evaluation of Spectroscopic Detectors for LEU Hold-up Measurements. United States: N. p., 2016. Web. doi:10.2172/1335357.
Venkataraman, Ramkumar, Nutter, Greg, & McElroy, Robert Dennis. Performance Evaluation of Spectroscopic Detectors for LEU Hold-up Measurements. United States. https://doi.org/10.2172/1335357
Venkataraman, Ramkumar, Nutter, Greg, and McElroy, Robert Dennis. Tue . "Performance Evaluation of Spectroscopic Detectors for LEU Hold-up Measurements". United States. https://doi.org/10.2172/1335357. https://www.osti.gov/servlets/purl/1335357.
@article{osti_1335357,
title = {Performance Evaluation of Spectroscopic Detectors for LEU Hold-up Measurements},
author = {Venkataraman, Ramkumar and Nutter, Greg and McElroy, Robert Dennis},
abstractNote = {The hold-up measurement of low-enriched uranium materials may require use of alternate detector types relative to the measurement of highly enriched uranium. This is in part due to the difference in process scale (i.e., the components are generally larger for low-enriched uranium systems), but also because the characteristic gamma-ray lines from 235U used for assay of highly enriched uranium will be present at a much reduced intensity (on a per gram of uranium basis) at lower enrichments. Researchers at Oak Ridge National Laboratory examined the performance of several standard detector types, e.g., NaI(Tl), LaBr3(Ce), and HPGe, to select a suitable candidate for measuring and quantifying low-enriched uranium hold-up in process pipes and equipment at the Portsmouth gaseous diffusion plant. Detector characteristics, such as energy resolution (full width at half maximum) and net peak count rates at gamma ray energies spanning a range of 60–1332 keV, were measured for the above-mentioned detector types using the same sources and in the same geometry. Uranium enrichment standards (Certified Reference Material no. 969 and Certified Reference Material no. 146) were measured using each of the detector candidates in the same geometry. The net count rates recorded by each detector at 186 keV and 1,001 keV were plotted as a function of enrichment (atom percentage). Background measurements were made in unshielded and shielded configurations under both ambient and elevated conditions of 238U activity. The highly enriched uranium hold-up measurement campaign at the Portsmouth plant was performed on process equipment that had been cleaned out. Therefore, in most cases, the thickness of the uranium deposits was less than the “infinite thickness” for the 186 keV gamma rays to be completely self-attenuated. Because of this, in addition to measuring the 186 keV gamma, the 1,001 keV gamma ray from 234mPa—a daughter of 238U in secular equilibrium with its parent—will also need to be measured. Based on the performance criteria of detection efficiency, energy resolution, peak-to-continuum ratios, minimum detectable limits, and the weight of the shielded probe, a shielded (0.5 in. thick lead shield) 2 × 2 in. NaI(Tl) detector is recommended for use. The recommended approach is to carry out analysis using data from both 186 keV and 1,001 keV gamma rays, and select a best result based on propagated uncertainty estimates. It is also highly recommended that a two-point gain stabilization scheme based on an 241Am seed embedded in the probe be implemented. Shielding configurations to reduce the impact of background interference on the measurement of 1,001 keV gamma-ray are discussed.},
doi = {10.2172/1335357},
url = {https://www.osti.gov/biblio/1335357}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2016},
month = {12}
}