Maximum Likelihood Spectrum Decomposition for Isotope Identification and Quantification

• Published in: IEEE transactions on nuclear science Vol. 69; no. 6; pp. 1212 - 1224
• Main Authors: Matta, J. T., Rowe, A. J., Dion, M. P., Willis, M. J., Nicholson, A. D., Archer, D. E., Wightman, H. H.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-06-2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Calibration; Cesium 137; Cesium isotopes; Cesium radioisotopes; Decomposition; Detectors; Deviation; Effluent streams; Gamma rays; Gamma spectroscopy; Gamma-ray detection; gamma-ray detectors; gamma-ray spectroscopy; Germanium; Government; Inverse problems; isotope identification; Isotopes; maximum likelihood expectation maximization (MLEM); Monitoring; Monte Carlo methods; nuclear measurements; NUCLEAR PHYSICS AND RADIATION PHYSICS; nuclide identification; Outliers (statistics); radioactive decay; Radioisotopes; semiconductor radiation detectors; Shielding; Spectra; spectral analysis; spectral decomposition; Spectroscopy
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2022.3162986

A spectral decomposition method has been implemented to identify and quantify isotopic source terms in high-resolution gamma-ray spectroscopy in static geometry and shielding scenarios. Monte Carlo simulations were used to build the response matrix of a shielded high-purity germanium detector monitoring an effluent stream with a Marinelli configuration. The decomposition technique was applied to a series of calibration spectra taken with the detector using a multi-nuclide standard. These results are compared with decay-corrected values from the calibration certificate. For most nuclei in the standard ( 241 Am, 109 Cd, 137 Cs, and 60 Co), the deviations from the certificate values were generally no more than 6% with a few outliers as high as 10%. For 57 Co, the radionuclide with the lowest activity, the deviations from the standard reached as high as 25%, driven by the meager statistics in the calibration spectra. In addition, a complete treatment of error propagation for the technique is presented.