Traceability of measurements of radioactivity and of amount of substance

Comparability of measurement results in space and time are highly desirable to observe whether differences are real, whether concordance of results is real and whether trends over time of the quantity measured, are significant. The metrological way to achieve this, is to make results 'traceable' to a common 'stated reference' (definition in the Vocabulaire International de Metrologie-VIM). This 'stated reference' should be (the value of) the relevant SI unit wherever and whenever possible. The latest traceability concepts for results of measurements of radioactivity and amount of substance are presented and critically compared for their similarity. Transparent and simple pictures of traceability chains are given, respecting the VIM definition.

Equivalence in radionuclide metrology

The harmonization of different National Measurement Systems depends on the ability to demonstrate Equivalence between them. The responsibility for establishing a procedure to achieve this lies with the International Committee of Weights and Measures (CIPM) and its associated Consultative Committees. In pursuit of these ends, a series of general recommendations and procedures have been developed by BIPM in order to achieve these objectives. Central to these recommendations is the concept of Key Comparisons which involve a series of comparison exercises both within and between the regional metrology organizations, such as EUROMET, NORAMET and APMP. Because of the unique nature of radioactivity standardization, this generalized procedure is, for practical purposes, impossible to apply in the field of radionuclide metrology. The remedy has been the development of a protocol which optimizes both the current effort available within existing National Metrology Institutes (NMIs) and the considerable amount of data from previous intercomparisons. This paper details this novel approach, provides practical examples, discusses potential problems and examines the way in which the programme will continue and expand.

Standardisation of 204Tl at IRMM

IRMM participated in a recent international comparison for the standardisation of a 204Tl solution organised by BIPM. The activity concentration of the 204Tl solution was measured at IRMM using 3 independent methods; Liquid Scintillation Counting using the CIEMAT/NIST method, 4pi-CsI counting and 4pibeta counting using a large pressurised proportional counter. This article describes the measurements in detail and discusses potential problems in the standardisation of 204Tl.