Equivalence in radionuclide metrology

Radionuclide metrology: confidence in radioactivity measurements

Radionuclides, whether naturally occurring or artificially produced, are readily detected through their particle and photon emissions following nuclear decay. Radioanalytical techniques use the radiation as a looking glass into the composition of materials, thus providing valuable information to various scientific disciplines. Absolute quantification of the measurand often relies on accurate knowledge of nuclear decay data and detector calibrations traceable to the SI units. Behind the scenes of the radioanalytical world, there is a small community of radionuclide metrologists who provide the vital tools to convert detection rates into activity values. They perform highly accurate primary standardisations of activity to establish the SI-derived unit becquerel for the most relevant radionuclides, and demonstrate international equivalence of their standards through key comparisons. The trustworthiness of their metrological work crucially depends on painstaking scrutiny of their methods and the elaboration of comprehensive uncertainty budgets. Through meticulous methodology, rigorous data analysis, performance of reference measurements, technological innovation, education and training, and organisation of proficiency tests, they help the user community to achieve confidence in measurements for policy support, science, and trade. The author dedicates the George Hevesy Medal Award 2020 to the current and previous generations of radionuclide metrologists who have devoted their professional lives to this noble endeavour.

Standardisation of 241Am activity for a key comparison

The JRC applied six measurement techniques to standardise the activity of an 241Am solution in the frame of the 2003 key comparison CCRI(II)-K2.Am-241. The methods used were alpha-particle counting at a defined small solid angle, high-efficiency particle and photon counting with a windowless 4π CsI(Tl) sandwich spectrometer, 4π alpha counting with a pressurised proportional counter, alpha-gamma coincidence counting and sum counting with a small pressurised proportional counter and a NaI(Tl) well detector, and 4π counting with a liquid scintillation counter. All results were consistent and an unusually low measurement uncertainty of 0.054% was achieved. An overview is presented of the outcome of the key comparison exercise, which demonstrates international equivalence.

Results from APMP comparisons on radioactivity measurements of 58Co, 88Y and 166mHo

International comparisons on radioactivity measurements of 55Co, 88Y and 166mHo were carried out within the framework of the Asia-Pacific Metrology Programme. Radioactive sources were also sent to the International Reference System (SIR) at the Bureau International des Poids et Mesures (BIPM) in order to link the results of these regional comparisons to the BIPM key comparison-reference values. The arithmetic mean for the activity results of 166mHo was in good agreement with the SIR reference value, but some disagreements were found for 58Co and 88Y results. The mean values for 58Co and 88Y were both higher than the existing SIR values by about 1.5% and 0.9%, respectively. Although there were some disagreements, it was successfully demonstrated that these regional comparisons could be linked to other international key comparisons through the SIR. The present results were also evaluated to estimate a reasonable uncertainty level for each laboratory, which is very important in the establishment of an adequate traceability scheme for radioactivity standards.