J. Rogers, “Modeling Study of Proposed Field Calibration Source Using K-40 Source and High-Z Targets for Sodium Iodide Detector”, M.S. Thesis, Health Physics, Texas A&M University, College Station, TX (2012).
The Department of Energy (DOE) has ruled that all sealed radioactive sources, even those considered exempt under Nuclear Regulatory Commission regulations, are subject to radioactive material controls. However, sources based on the primordial isotope 40K are not subject to these restrictions. 40K’s beta and gamma emissions could be used to produce x-rays in a high-Z metal and provide a second photon peak. A gamma ray calibration source is proposed that uses potassium chloride salt and a high-Z metal to create a two-point calibration for a sodium iodide field gamma spectroscopy instrument.
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 cheap, nontoxic, and outperformed the HZL method in simulation. The potassium chloride-bismuth-based calibration source would serve as a light, cheap, field calibration source that is not subject to DOE restrictions.