The international reference system for pure beta-particle emitting radionuclides: an evaluation of the measurement uncertainties

Abstract

The international bureau of weights and measures (BIPM) is the centre for governments to act in common on matters relating to metrology, co-ordinating the world-wide measurement system and providing capabilities for international measurement comparisons on a shared-cost basis. The ionizing radiation department maintains and develops high-precision instrumentation to enable national metrology institutes to demonstrate the equivalence of primary standards of radioactivity. The scope of this service is expanding: the ‘extended international reference system (ESIR)’ project aims to provide a stable instrument capable of comparing standards of pure beta-emitting radionuclides, complementing existing instruments for gamma-emitters. In 2019, the members of the ESIR project devised a liquid scintillation system that is capable of producing very stable reference values over a long timescale, using a method inspired by the ‘triple-to-double coincidence ratio’ (TDCR) technique. This article sets out the approach that will be used for evaluating uncertainties in future comparison exercises using the ESIR. The method adopted was based on the guide to the expression of uncertainty in measurement published by the joint committee for guides in metrology. Particular care has been taken in choosing the evaluation method: the response of the TDCR instrument cannot be linearized, so a Monte-Carlo method was implemented and a technique to manage correlated input data was developed. A novel sampling technique was used for the input multi-variate distribution of coincident count rates; this approach may also be relevant to primary standards realized using the TDCR technique. Calculation have shown that standard uncertainties of the order of 0.1 % will be achievable for a typical radionuclide.

Digitalization of the reporting of key comparisons for radionuclide metrology

“…A machine-readable version of the database is also produced and will pave the way to enable users to interact with the data for novel research purposes. In the meantime, the process will be extended to other services in radionuclide metrology: the SIRTI [32] addressing more particularly short-lived radionuclides and the ESIR [33,34] addressing pure alpha and beta-emitting radionuclides.…”

Traceability for nuclear medicine: the status of primary radioactivity standards

“…To date, three instruments (the SIR, the SIRTI and the ESIR) have been developed for comparing standards of gamma-ray-emitting radionuclides and pure alpha-and betaparticle-emitting radionuclides, respectively. The ESIR was launched recently (2020), so results from this instrument have yet to be published, but a pilot study measuring 60 Co standards is ongoing to test the ESIR against the SIR [7][8][9].…”

Evaluation of the Long-Term Stability of Metrology Instruments

“…Two data are here considered. The first one comes from the periodic control of a recent metrology system that operates at the BIPM for radionuclide metrology and is called the ESIR (extended SIR) [11,12]. The second example comes from the periodic control of a metrology service, the SIR, which operates at the BIPM for radionuclide metrology since 1976 [13].…”