ABSTRACT
The Bureau International des Poids et Mesures (BIPM) is developing a new transfer instrument to extend its centralized services for assessing the international equivalence of radioactive standards to new radionuclides. A liquid scintillation counter using the triple/double coincidence ratio method is being studied and tested in the CCRI(II)-P1.Co-60 pilot study. The pilot study, involving 13 participating laboratories with primary calibration capabilities, validated the approach against the original international reference system based on ionization chambers, which has been in operation since 1976. The results are in agreement and an accuracy suitable for purpose, below 5×10-4, is achieved. The pilot study also reveals an issue when impurities emitting low-energy electrons are present in the standard solution, which have a different impact on liquid scintillation counting compared to other primary measurement methods.
ABSTRACT
A new (18)F primary standardization carried out at ENEA-INMRI by three different absolute techniques, i.e. 4πγNaI(Tl)γ high-efficiency counting, TDCR and 4πß(LS)-γ[NaI(Tl)] coincidence counting method, allowed the calibration of a fixed well-reentrant IG11 ionization chamber (IC), with an uncertainty lower than 1%, and to check the calibration factor of a portable well-type IC NPL-CRC model, previously calibrated. By the new standard the ENEA-INMRI was linked to the BIPM International Reference System (SIR) through the BIPM SIR Transfer Instrument (SIRTI).
