The standardization of a 204Tl solution

60 years of absolute standardization of radionuclides by coincidence counting methods in the Romanian metrology laboratory

This review paper presents the contribution of the Radionuclide Metrology Laboratory (RML) to the development and practical application of the coincidence counting methods. It is also intended to pay tribute to Dr. Enric Leon Grigorescu, the founder of our school of radionuclide metrology. A synthetic treatment of the method, applied to some classes of radionuclides with their common and particular aspects in standardization, is presented: pioneering calculation of instrumental corrections, specific method corrections applied for various types of decay schemes in the variant of efficiency extrapolation, results obtained in international comparisons.

Primary standardisation of 204Tl using the efficiency tracing method

The electron-capture and beta(-) -emitting radionuclide 204Tl has been known from previous experience to show discrepancies between different methods of standardisation. Source preparation is also difficult due to the complex chemistry of thallium. The Bureau International des Poids et Mesures (BIPM) intercomparison held in 1997, showed discrepancies of up to 10% between measurements of solid sources and liquid scintillation methods. These problems have been the subject of a BIPM CCRI(II) working group since 1999. This paper presents the results from a primary standardisation of a 204Tl solution using 4pibeta-gamma coincidence counting and liquid scintillation counting. The tracer technique was used for the 4pibeta-gamma coincidence counting, where 204Tl was traced with 134Cs and 60Co. The extrapolation to 100% beta-efficiency was performed by three different approaches: foiling, adding carrier and measuring sources of different initial masses. The results showed that tracing with 60Co and using external foiling gave the same result as obtained by liquid scintillation counting. A comparison of the results achieved by the different methods of measurement, tracers and methods for extrapolation is presented and discussed in this paper.

Standardization of 89Sr

Two methods were used for the standardization of the pure beta-emitter 59Sr solution received in the framework of the 2000 BIPM comparison of activity measurements. The first method was by scintillation counting using the triple to double coincidence ratio (TDCR) technique. The existing three detector-system was improved by the inclusion of a MAC-3 module produced by LNHB-Saclay. This module contains the circuits for the coincidence, dead time and gate functions. This was the first use of this equipment in an international comparison. The DETECSZ program (LNHB) was used to obtain the activity concentration, at the reference time, as 26.09+/-0.21 kBq g(-1). The second method was the efficiency tracer technique, using a 60Co standard solution and a 4pi beta-gamma-coincidence system. The radioactivity concentration was calculated from a general extrapolation curve, by using data from several sources. The value was 26.58+/-0.28 kBq g(-1) on the reference date 01.10.2000, 00 h UTC. The two results are in agreement within the limits of their combined uncertainties.