Effects of Correlated and Uncorrelated Gamma Rays on Neutron Multiplicity Counting

• Published in: IEEE transactions on nuclear science Vol. 64; no. 7; pp. 1865 - 1870
• Main Authors: Cowles, Christian C., Behling, Richard S., Imel, George R., Kouzes, Richard T., Lintereur, Azaree T., Robinson, Sean M., Siciliano, Edward R., Stave, Sean C.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-07-2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Assaying; Coincidence counting; Correlation analysis; Detectors; Electronic mail; Fission; Gamma rays; gamma-ray detection; gamma-ray effects; gamma-rays detection; Logic gates; Mathematical model; Multiplication; multiplicity counting; Neutrons; neutrons detectors; NUCLEAR PHYSICS AND RADIATION PHYSICS; Radiation detectors; time correlated; uncorrelated
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2017.2667407

Neutron multiplicity counting relies on time correlation between neutron signals to assay the fissile mass, (α,n) to spontaneous fission neutron ratio, and neutron self-multiplication of samples. Gamma-ray sensitive neutron multiplicity counters may misidentify gamma rays as neutrons and therefore miscalculate sample characteristics. Time correlated and uncorrelated gamma-ray-like signals were added into gamma-ray free neutron multiplicity counter data to examine the effects of gamma-ray signals being misidentified as neutron signals on assays. Multiplicity counter measurements with and without gamma-ray-like signals were compared to determine the assay error associated with gamma-ray-like signals at various gamma-ray and neutron rates. Correlated and uncorrelated gamma-ray signals each produced consistent but different measurement errors. Correlated gamma-ray signals most strongly led to fissile mass overestimates, whereas uncorrelated gamma-ray signals most strongly lead to (α,n) neutron overestimates. Accounting for the effects of gamma rays on gamma-ray sensitive neutron multiplicity counters may allow these effects to be compensated for, thus mitigating the assay error associated with misidentified gamma rays.