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Title: Tomographic Gamma Scanning (TGS) Algorithms

  1. Los Alamos National Laboratory
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Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
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Conference: Spent Fuel Non-Destructive Assay (NDA) Annual Project Meeting ; 2017-10-25 - 2017-10-25 ; Los Alamos, New Mexico, United States
Country of Publication:
United States

Citation Formats

Estep, Robert Jerome. Tomographic Gamma Scanning (TGS) Algorithms. United States: N. p., 2017. Web.
Estep, Robert Jerome. Tomographic Gamma Scanning (TGS) Algorithms. United States.
Estep, Robert Jerome. 2017. "Tomographic Gamma Scanning (TGS) Algorithms". United States. doi:.
title = {Tomographic Gamma Scanning (TGS) Algorithms},
author = {Estep, Robert Jerome},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month =

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  • This paper describes the design and testing of a novel automated Wide Range Segmented Gamma ray Scanning (WR-SGS) assay instrument that also incorporates Tomographic Gamma Scanning (TGS). The instrument is designed for the measurement of both Low and Intermediate Level Waste (LLW and ILW) in 200 litre drums and other waste containers covering a wide range of density. Like earlier ANTECH WR-SGS instruments, the system employs a single shielded and collimated high purity germanium (HPGe) detector to quantify the radionuclide content of the waste and like conventional SGS instruments it is suitable for the measurement of relatively homogeneous waste matrices.more » Also, like earlier WR-SGS systems the instrument incorporates an automated variable aperture collimator, which allows the vertical segment height to be adjusted in order to measure both high dose-rate and very low activity drums. The instrument employs both conventional discrete SGS vertical segment measurements as well as vertical segment measurement by continuous helical-scanning of the drum as it rotates. This latter method reduces measurement times for SGS measurements. In order to determine the density corrections for both low and high-density drums, a high activity Eu-152 transmission source is employed. When not in use, and in place of a conventional shutter mechanism, the shielded transmission source is moved to a shielded storage position to eliminate background radiation from the source. Due to its novel features, the WR-SGS is applicable to the measurement of both very low and very high activity waste drums as well as waste drums with a wide range of density. If located in a low background position and with the effective shielding of the strong transmission source, the instrument can be used to measure very low level or exempt waste. In order to extend the range of applicability to the measurement of heterogeneous drums, TGS measurement capability has been included in the basic WR-SGS design. This is achieved by adding horizontal motion to the waste drum rotation platform and incorporating TGS collimation into the variable aperture collimator, as well as a filter to reduce the detector signal when straight-through measurements are made using the strong transmission source. Test measurements are presented of the system operating in both SGS and TGS modes using different drum densities and source strengths. The test measurement results are compared with benchmarked MCNP Monte Carlo calculations. The Wide Range SGS - TGS instrument extends the range of both activity and density that can be measured in 200 and 340 litre drums. (authors)« less
  • A tomographic gamma-ray scanning (TGS) instrument was deployed at Rocky Flats Environmental Technology Site (RFETS) to assist with the deactivation of Building 886. Many 208-L drums containing waste contaminated with highly enriched uranium were measured in order to certify these sites for shipment and disposal. This project marks a successful cooperation between RFETS and Los Alamos National Laboratory and is the first major field experience using TGS technology to assay uranium.
  • Field experience with the tomographic gamma scanner to assay nuclear material suggests that the analysis techniques can significantly impact the assay uncertainty. For example, currently implemented image reconstruction methods exhibit a positive bias for low-activity samples. Preliminary studies indicate that bias reduction could be achieved at the expense of increased random error variance. In this paper, the authors examine three possible bias sources: (1) measurement error in the estimated transmission matrix, (2) the positivity constraint on the estimated mass of nuclear material, and (3) improper treatment of the measurement error structure. The authors present results from many small-scale simulation studiesmore » to examine this bias/variance tradeoff for a few image reconstruction methods in the presence of the three possible bias sources.« less
  • The authors examined two approaches for using NaI detectors to perform transmission corrections used in the tomographic gamma scanner (TGS) and segmented gamma scanner (SGS) nondestructive assay methods. They found that a material-basis-set (MBS) fit using empirical logarithmic response spectra is quite accurate. Because this is a gross count technique, it gives sensitivities (for equal numbers of detectors) that are roughly ten times better than those obtained using Germanium detectors. The authors also found that simple continuum subtraction can be used in MBS fits using the energy-group-analysis technique only when the Pu transmission is greater than 10%. Both approaches formore » using NaI detectors require a knowledge of the Pu (or other) isotopics to obtain full accuracy.« less