Quantifying uncertainty in nuclear analytical measurements

The lack of international consensus on the expression of uncertainty in measurements was recognised by the late 1970s and led, after the issuance of a series of rather generic recommendations, to the publication of a general publication, known as GUM, the Guide to the Expression of Uncertainty in Measurement. This publication, issued in 1993, was based on co-operation over several years by the Bureau International des Poids et Mesures, the International Electrotechnical Commission, the International Federation of Clinical Chemistry, the International Organization for Standardization (ISO), the International Union of Pure and Applied Chemistry, the International Union of Pure and Applied Physics and the Organisation internationale de metrologie legale. The purpose was to promote full information on how uncertainty statements are arrived at and to provide a basis for harmonized reporting and the international comparison of measurement results. The need to provide more specific guidance to different measurement disciplines was soon recognized and the field of analytical chemistry was addressed by EURACHEM in 1995 in the first edition of a guidance report on Quantifying Uncertainty in Analytical Measurements, produced by a group of experts from the field. That publication translated the general concepts of the GUM into specific applications for analytical laboratories and illustrated the principles with a series of selected examples as a didactic tool. Based on feedback from the actual practice, the EURACHEM publication was extensively reviewed in 1997-1999 under the auspices of the Co-operation on International Traceability in Analytical Chemistry (CITAC), and a second edition was published in 2000. Still, except for a single example on the measurement of radioactivity in GUM, the field of nuclear and radiochemical measurements was not covered. The explicit requirement of ISO standard 17025:1999, General Requirements for the Competence of Testing and Calibration Laboratories to quantify the uncertainty of measurement results, and the fact that this standard is used as a basis for the development and implementation of quality management systems in many laboratories performing nuclear analytical measurements, triggered the demand for specific guidance to cover uncertainty issues of nuclear analytical methods. The demand was recognized by the IAEA and a series of examples was worked out by a group of consultants in 1998. The diversity and complexity of the topics addressed delayed the publication of a technical guidance report, but the exchange of views among the experts was also beneficial and led to numerous improvements and additions with respect to the initial version. This publication is intended to assist scientists using nuclear analytical methods in assessing and quantifying the sources of uncertainty of their measurements. The numerous examples provide a tool for applying the principles elaborated in the GUM and EURACHEM/CITAC publications to their specific fields of interest and for complying with the requirements of current quality management standards for testing and calibration laboratories. It also provides a means for the worldwide harmonization of approaches to uncertainty quantification and thereby contributes to enhanced comparability and competitiveness of nuclear analytical measurements