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Reduction of False Positives in the Identification of Nuclides in Environmental Samples

[+] Author Affiliations
Susan E. Haywood

ORTEC

Paper No. ICEM2003-4542, pp. 469-472; 4 pages
doi:10.1115/ICEM2003-4542
From:
  • ASME 2003 9th International Conference on Radioactive Waste Management and Environmental Remediation
  • 9th ASME International Conference on Radioactive Waste Management and Environmental Remediation: Volumes 1, 2, and 3
  • Oxford, England, September 21–25, 2003
  • Conference Sponsors: Nuclear Engineering Division and Environmental Engineering Division
  • ISBN: 0-7918-3732-7 | eISBN: 0-7918-3731-9
  • Copyright © 2003 by ASME

abstract

Gamma-ray spectra containing peaks that are too close in energy for deconvolution to be done accurately are best analyzed by a library-based method. However, a library-based analysis done with a large library may result an unacceptable number of false positives being reported. A normal working library suitable for analyzing environmental samples containing unknown materials may have over 1000 peaks, many of which are too close for deconvolution to be done accurately. A program has been written that uses a library-based analysis method that reduces the reporting of false positives, while retaining the ability to identify isotopes accurately from a large range of possibilities. In addition, the peak area calculation has been improved by allowing the energy calibration to be a free parameter in the fit of individual multiplets. This peak area improvement can result in a change of activity of several percent for some nuclides. In some cases, shifting the multiplet position can reduce false positives by identifying a peak in the multiplet as an unknown rather than associating it with a nuclide. One spectrum showed a marked peak activity improvement when the calibration was allowed to shift even though the the average error in the original calibration was 0.08%. Results obtained from a study on the identification of uranium decay products are presented.

Copyright © 2003 by ASME
Topics: Nuclides

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