Measurement,+uncertainty+and+Detection+Limits

In research laboratories and with service providers of radioisotope technology, the awareness for the necessity of implementing QA/QC systems to their activities has increased the last years. This is related to the fact that financing and income possibilities may strongly depend on it.

An integrated and inseparable part of QA/QC systems for R&D and services in radioisotope technology is procedures for reliable uncertainty estimates of the measured quantity and, especially in low-level radioanalytical tracer work, reliable procedures for correctly calculating detection and quantification limits.

Until late 1970s these topics had little attention. However, in 1993 the International Standardization Organization (ISO) published in collaboration with the Bureau International des Poids et Mesures (BIPM), the International Electrochemical Commission (IEC), the International Federation of Clinical Chemistry (IFCC), the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Pure and Applied Physics (IUPAP) and the International Organization of Legal Metrology (OIML), the “Guide to the Expression of Uncertainty in Measurement” (GUM). This document establishes general rules for evaluating and expressing uncertainty across a broad spectrum of measurements. A more user-friendly specific guide on “Quantifying Uncertainty in Analytical Measurement” was published in 1995 by EURACHEM. However, nuclear related measurement techniques were largely omitted. In co-operation with EURACHEM, the IAEA therefore initiated a work in 1998 dedicated to illustrate the quantification of uncertainty components for the most common nuclear and nuclear related analytical methods. A TECDOC on the subject was published in 2004. About the same time IAEA also published a training manual of QA for nuclear analytical techniques [5] and a technical report addressing QA in radioisotope applications. Ref.s [5] and do not treat details of measurement uncertainty.

The present text introduces principles of the measurement uncertainty evaluation and the concepts of decision, detection and quantitative determination limits. Such procedures should be included in QA/QC systems for all techniques under the umbrella entitled “radioisotope techniques” for which they are relevant. This subject may be considerably expanded in future work, including more complicated examples covering several radioisotope techniques.

Measurement Uncertainty Analysis
 * 1) Uncertainty and Errors
 * 2) Accuracy and Precision
 * 3) Uncertainty Classes, Significant Figures and Uncertainty Estimation
 * 4) Evaluation of Type A and Type B Uncertainties
 * 5) Probability and Distribution

Detection and Quantification