Description of BS EN ISO 11929-2:2021 2021

The ISO 11929 series specifies a procedure, in the field of ionizing radiation metrology, for the calculation of the “decision threshold”, the “detection limit” and the “limits of the coverage interval” for a non-negative ionizing radiation measurand when counting measurements with preselection of time or counts are carried out. The measurand results from a gross count rate and a background count rate as well as from further quantities on the basis of a model of the evaluation. In particular, the measurand can be the net count rate as the difference of the gross count rate and the background count rate, or the net activity of a sample. It can also be influenced by calibration of the measuring system, by sample treatment and by other factors.

ISO 11929 has been divided into four parts covering elementary applications in ISO 11929‑1, advanced applications on the basis of the GUM Supplement 1 in this document, applications to unfolding methods in ISO 11929‑3, and guidance to the application in ISO 11929‑4.

ISO 11929‑1 covers basic applications of counting measurements frequently used in the field of ionizing radiation metrology. It is restricted to applications for which the uncertainties can be evaluated on the basis of the ISO/IEC Guide 98‑3 (JCGM 2008). In Annex A of ISO 11929‑1:2019 the special case of repeated counting measurements with random influences is covered, while measurements with linear analogous ratemeters are covered in Annex B of ISO 11929‑1:2019.

This document extends the former ISO 11929:2010 to the evaluation of measurement uncertainties according to the ISO/IEC Guide 98‑3‑1. It also presents some explanatory notes regarding general aspects of counting measurements and on Bayesian statistics in measurements.

ISO 11929‑3 deals with the evaluation of measurements using unfolding methods and counting spectrometric multi-channel measurements if evaluated by unfolding methods, in particular, for alpha- and gamma‑spectrometric measurements. Further, it provides some advice on how to deal with correlations and covariances.

ISO 11929‑4 gives guidance to the application of ISO 11929, summarizes shortly the general procedure and then presents a wide range of numerical examples. Information on the statistical roots of ISO 11929 and on its current development may be found elsewhere^[30,31].

ISO 11929 also applies analogously to other measurements of any kind especially if a similar model of the evaluation is involved. Further practical examples can be found, for example, in ISO 18589^[1], ISO 9696^[2], ISO 9697^[3], ISO 9698^[4], ISO 10703^[5], ISO 7503^[6], ISO 28218^[7], and ISO 11885^[8].

NOTE A code system, named UncertRadio, is available for calculations according to ISO 119291 to ISO 11929‑3. UncertRadio^[27][28] can be downloaded for free from /2. The download contains a setup installation file which copies all files and folders into a folder specified by the user. After installation one has to add information to the PATH of Windows as indicated by a pop‑up window during installation. English language can be chosen and extensive “help” information is available. . Another tool is the package ‘metRology’^[32] which is available for programming in R. It contains the two R functions ‘uncert’ and ‘uncertMC’ which perform the GUM conform uncertainty propagation, either analytically or by the Monte Carlo method, respectively. Covariances/correlations of input quantities are included. Applying these two functions within iterations for decision threshold and the detection limit calculations simplifies the programming effort significantly. It is also possible to implement this part of ISO 11929 in a spreadsheet containing a Monte Carlo add-in or into other commercial mathematics software.

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