Revisiting the activity standardisation of ¹⁷⁷Lu

Area of Science:

• Nuclear physics
• Radiochemistry
• Metrology

Background:

• Previous ¹⁷⁷Lu standardization using beta-gamma coincidence with plastic scintillators yielded results discrepant by 2% compared to the TDCR method.
• Similar discrepancies between solid source coincidence counting and liquid scintillation measurements have been previously reported in radionuclide metrology.

Purpose of the Study:

• To revisit and resolve the observed discrepancies in ¹⁷⁷Lu activity standardization.
• To compare results from beta-gamma coincidence counting (using plastic and liquid scintillators) with TDCR and CNET methods for ¹⁷⁷Lu.
• To investigate the behavior of efficiency functions in coincidence counting at different efficiency ranges.

Main Methods:

• Standardization of a ¹⁷⁷Lu solution using the beta-gamma coincidence technique with both plastic and liquid scintillation detectors.
• Application of the Triple-to-Double Coincidence Ratio (TDCR) and CNET methods for cross-validation.
• Analysis of coincidence counting efficiency functions across a higher efficiency range using plastic sources.

Main Results:

• The study explored higher efficiency ranges for coincidence counting with plastic sources, revealing different behaviors of efficiency functions at high and low efficiencies.
• Extrapolating efficiency using a linear function in the high range or a non-linear curve across the entire span reconciled the results.
• The revised coincidence counting methods yielded activities in agreement with liquid scintillation counting determinations, resolving the initial discrepancy.

Conclusions:

• The discrepancy in ¹⁷⁷Lu activity standardization between beta-gamma coincidence counting with plastic scintillators and the TDCR method has been resolved.
• Accurate extrapolation of efficiency functions is crucial for reliable beta-gamma coincidence counting, especially when using solid sources.
• This work improves the accuracy and reliability of ¹⁷⁷Lu activity measurements, vital for its use in nuclear medicine and research.