Bioassay alpha spectrometry: energy resolution as a function of sample source preparation and counting geometry

Area of Science:

• Nuclear Science and Engineering
• Analytical Chemistry
• Environmental Monitoring

Background:

• Alpha particle counting relies on electronic detection systems.
• Alpha spectrometry is crucial for employee surveillance bioassays.
• Accurate quantification of isotopes like Americium (Am), Plutonium (Pu), and Uranium (U) is essential for safety.

Purpose of the Study:

• To describe an alpha spectrometry method for measuring Am, Pu, and U in employee bioassays.
• To detail the use of tracers for quality control and chemical yield determination.
• To assess the performance and limitations of the alpha spectrometry system.

Main Methods:

• Anion exchange separation and electroplating of Am, Pu, and U onto stainless steel discs.
• Addition of a tracer before separation to calculate chemical recovery and yield.
• Counting of electroplated samples using a system of 96 detectors with low background rates (< 3 counts/70,000 s).

Main Results:

• The tracer method provides a reliable estimate of analyte counts and assesses spectrometer performance.
• Low detector backgrounds (< 0.37 mBq detection limit) are achieved.
• Photopeak resolution is influenced by source-detector distance and sample contaminants, but is adequate for low-activity samples (< 0.2 Bq) with < 50 keV FWHM resolution.

Conclusions:

• The described alpha spectrometry method, utilizing tracers, is effective for quantifying Am, Pu, and U in employee bioassay programs.
• The system's performance, including low detection limits and adequate resolution, supports reliable monitoring of low-level radioactivity.
• Quality control measures, such as tracer recovery, ensure the accuracy and dependability of the bioassay results.