Modeling Study of a Proposed Field Calibration Source Using K-40 and High-Z Targets for Sodium Iodide Detectors.
Calibration sources based on the primordial isotope potassium-40 (K) have reduced controls on the source's activity due to its terrestrial ubiquity and very low specific activity. Potassium-40's beta emissions and 1,460.8 keV gamma ray can be used to induce K-shell fluorescence x rays in high-Z metals between 60 and 80 keV. A gamma ray calibration source that uses potassium chloride salt and a high-Z metal to create a two-point calibration for a sodium iodide field gamma spectroscopy instrument is thus proposed. The calibration source was designed in collaboration with the Sandia National Laboratory using the Monte Carlo N-Particle eXtended (MCNPX) transport code. Two methods of x-ray production were explored. First, a thin high-Z layer (HZL) was interposed between the detector and the potassium chloride-urethane source matrix. Second, bismuth metal powder was homogeneously mixed with a urethane binding agent to form a potassium chloride-bismuth matrix (KBM). The bismuth-based source was selected as the development model because it is inexpensive, nontoxic, and outperforms the high-Z layer method in simulation. Based on the MCNPX studies, sealing a mixture of bismuth powder and potassium chloride into a thin plastic case could provide a light, inexpensive field calibration source.
*National Security Technologies, Remote Sensing Laboratory, PO Box 89521, Las Vegas, NV; †Nuclear Security Science and Policy Institute, Texas A&M University, 3473 TAMU, College Station, TX; ‡Sandia National Laboratory, PO Box 5800 MS0671, Albuquerque, NM; §Department of Nuclear Engineering, Texas A&M University, 3473 TAMU, College Station, TX.
Jeremy
J
Rogers
Craig
C
Marianno
Gene
G
Kallenbach
Jose
J
Trevino
D002138:Calibration / Q000592:standards; D003198:Computer Simulation; D015233:Models, Statistical; D009010:Monte Carlo Method; D011194:Potassium Isotopes / Q000032:analysis* / Q000592:standards*; D012016:Reference Values; D015203:Reproducibility of Results; D012588:Scintillation Counting / Q000295:instrumentation* / Q000592:standards*; D012680:Sensitivity and Specificity; D012974:Sodium Iodide / Q000528:radiation effects*
D011194:Potassium Isotopes; D012974:Sodium Iodide