PSD Performance using CLYC Scintillation Detector for Special Nuclear Materials Measurement

As nuclear material uses and procedures continue to advance globally, it is important to develop improved methods for rapid categorization and characterization of radiation signature data in order to ensure safeguard measures for the modern nuclear environment. This requires using detector systems capable of detecting and distinguishing complex, multi-variant radiation fields. Detailed gamma-energy spectrums of special nuclear materials and advanced pulse shaped discrimination analysis can aid in development of improved techniques and eventual applications to machine learning techniques for rapid classification of special radiological materials. The National Criticality Experiments Research Center (NCERC), operated for the DOE Nuclear Criticality Safety Program, and funded and managed by the National Nuclear Security Administration, provides unique access for conducting measurements with special nuclear materials at the Nevada National Security Site (NNSS). This research utilized a Cs2LiYCl6:Ce3+(CLYC) scintillation detector to conduct measurements against Rocky Flats (RF) Hemishells, which are nesting hemishells of highly enriched uranium (HEU), and a Beryllium-Reflected Plutonium (BeRP) ball, which is a sphere of weapons-grade (WG) plutonium at the NCERC. The Cs2LiYCl6:Ce3+(CLYC) scintillation detectors are known for detecting both slow and fast neutrons and have good gamma-ray spectroscopy capabilities. The 6Li(n, a)3H reaction allows for thermal neutrons to be measured while the 35Cl(n, p)35S and 35Cl(n, a)32P reactions allow for fast neutrons to be measured [1, 2, 3].  CLYC detectors normally have a better performance than commonly deployed NaI detectors, especially with its ability to achieve a higher energy resolution than NaI(Tl) scintillators [4, 5]. With that in mind, the CLYC is uniquely positioned for use for pulse shaped discrimination and to evaluate gamma energy spectrums for a variety of special nuclear materials. Digitized CLYC pulse, using a STRUCK SIS3316 digitizer, was tested for various pulse features to use in pulse shape discrimination, with and without pulse-smoothing. This research evaluated six different pulse parameters to refine four unique PSD scripts and evaluate their performance for the CLYC detector. The results generated gamma-ray spectra for RF HEU and BeRP WG Pu. Additionally, the data that was obtained and resulting PSD metric refinement will enable development of future ML/data algorithms that can decrease the amount of time needed to characterize complex, multi-variant radiation fields from modern nuclear programs.