Results of an international comparison of activity measurements of 68Ge

An international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a 68Ge/68Ga solution. Results for the activity concentration, CA, of 68Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)β-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11)kBqg-1, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence.

The absolute counting of 125I

The Institute of Nuclear Energy Research (INER) participated in a comparison of activity organized by the Electrotechnical Laboratory (ETL, Japan). At this occasion, 125I was measured. Seven laboratories of the Asia Pacific region carried out measurements and ETL, at the same time, took part in BIPM SIR measurements. Two measurement methods developed by INER, the sum-peak coincidence counting with two 76 x 76 mm NaI(Tl) detectors and the 4pie-X coincidence counting technique with efficiency extrapolation, were used to standardize the activity of 125I. The results from the two methods are 2.6% different. INER's results agree with the results of the regional comparison and the BIPM SIR.