Modeling Study of a Proposed Field Calibration Source Using K-40 and High-Z Targets for Sodium Iodide Detectors.

Area of Science:

• Nuclear Physics
• Analytical Chemistry
• Materials Science

Background:

• Potassium-40 (K) is a primordial isotope with low specific activity, posing challenges for calibration source development.
• Potassium-40's beta emissions and 1,460.8 keV gamma rays can induce K-shell fluorescence X-rays in high-Z metals.

Purpose of the Study:

• To propose and design a novel, inexpensive, and portable gamma ray calibration source for field gamma spectroscopy.
• To create a two-point calibration method for sodium iodide detectors using potassium-40 induced X-rays.

Main Methods:

• Utilized Monte Carlo N-Particle eXtended (MCNPX) transport code for simulation and design.
• Investigated two X-ray production methods: a high-Z layer (HZL) and a potassium chloride-bismuth matrix (KBM).
• Selected the bismuth-based KBM for its cost-effectiveness, low toxicity, and superior simulated performance.

Main Results:

• Simulations indicated that a potassium chloride-bismuth mixture outperforms the HZL method.
• The KBM approach allows for the generation of K-shell fluorescence X-rays in bismuth (60-80 keV).
• A sealed mixture of bismuth powder and potassium chloride in a plastic case is proposed as a viable calibration source.

Conclusions:

• A bismuth-based potassium-40 calibration source offers a practical solution for field gamma spectroscopy.
• The proposed source is light, inexpensive, and provides a reliable two-point calibration.
• This development enhances the capability for accurate radioactive material analysis in field settings.