Primary and secondary activity standards for ⁸⁹Zr

Area of Science:

• Nuclear Metrology
• Radiochemistry
• Applied Physics

Background:

• Accurate radionuclide activity standardization is crucial for nuclear medicine, environmental monitoring, and radiation protection.
• Previous standardizations by Physikalisch-Technische Bundesanstalt (PTB) reported larger than usual uncertainties.
• The National Institute of Standards and Technology (NIST) aimed to refine standardization methods and establish traceable secondary standards.

Purpose of the Study:

• To perform a primary standardization of radionuclide activity using Triple-to-Double Coincidence Ratio (TDCR) liquid scintillation counting.
• To develop and validate secondary standards for various solution volumes and container types.
• To improve the accuracy and reliability of radionuclide activity measurements through advanced modeling and comparisons.

Main Methods:

• Primary standardization was conducted using Triple-to-Double Coincidence Ratio (TDCR) liquid scintillation counting.
• CIEMAT/NIST efficiency tracing was employed for confirmation of the primary method.
• Detector-specific Monte Carlo modeling was utilized to correct for backscatter effects across a range of source volumes.

Main Results:

• The TDCR method yielded a combined standard uncertainty of 0.79%, with significant contributions from filter and scintillant variations.
• Secondary standards were successfully determined for 5 mL, 4 mL, 2 mL, and 1 mL solutions in various ampoules, vials, and syringes.
• Monte Carlo modeling improved the backscatter correction performance across different source volumes.

Conclusions:

• NIST successfully established primary and secondary standards for radionuclide activity, enhancing measurement traceability.
• The study highlights the importance of accounting for factors like source volume and detector characteristics in liquid scintillation counting.
• The developed secondary standards provide reliable reference points for calibrating various instruments, including ionization chambers and radionuclide calibrators.