ISO 11929-1:2019

Overview

ISO 11929-1:2019 - Determination of the characteristic limits (decision threshold, detection limit and limits of the coverage interval) for measurements of ionizing radiation - Part 1: Elementary applications - is an ISO standard that defines procedures for calculating the characteristic limits of a non‑negative ionizing radiation measurand in counting measurements. It covers basic counting‑measurement scenarios (preselected time or counts) where the measurand is derived from gross and background count rates and other evaluation model quantities (for example, net count rate or net activity). The standard is grounded in a Bayesian approach to measurement uncertainty and is aligned with ISO/IEC Guide 98‑3 (and extended guidance in ISO/IEC Guide 98‑3‑1).

Key topics and technical requirements

• Characteristic limits: definitions and calculation methods for the decision threshold, detection limit, and limits of the coverage interval (coverage interval replacing the term confidence interval).
• Measurement modelling: guidance on building an evaluation model relating gross counts, background counts, calibration factors, sample treatment and other influences to the measurand.
• Uncertainty treatment: evaluation of input quantities, standard uncertainties and covariances according to ISO/IEC Guide 98‑3 (with references to ISO/IEC Guide 98‑3‑1 for Monte Carlo methods in the series).
• Calculation procedures: stepwise summary for evaluating the primary result, deriving standard uncertainty as a function of assumed measurand values, computing decision threshold and detection limit, and determining coverage intervals.
• Special cases: Annex A covers repeated counting measurements with random influences; Annex B addresses measurements with linear analog ratemeters. Informative annexes provide iterative calculation notes and generalized net count rate handling.
• Bayesian foundations: characteristic values are defined via moments and quantiles of probability distributions; Monte Carlo propagation (ISO/IEC Guide 98‑3‑1) is supported for complex uncertainty propagation.

Applications and who uses it

ISO 11929-1:2019 is relevant to:

• Radiological protection and environmental monitoring laboratories
• Nuclear industry and radiochemistry labs performing activity measurements
• Calibration and metrology institutes assessing detection capabilities
• Regulatory bodies evaluating compliance decisions and reporting thresholds

Practical uses include establishing detection capability for low‑level alpha/gamma/beta counting, setting reporting thresholds for environmental radionuclide monitoring, and assessing whether measurement procedures meet requirement specifications.

Related standards and tools

• Related parts: ISO 11929‑2 (advanced applications, ISO/IEC Guide 98‑3‑1), ISO 11929‑3 (unfolding methods, spectrometry), ISO 11929‑4 (guidance/examples).
• Associated ISO standards: ISO 18589, ISO 9696–9698, ISO 10703, ISO 28218, ISO 11665 (practical examples and application contexts).
• Calculation tool: UncertRadio - an available code for ISO 11929‑1 to 11929‑3 computations (download from the Thünen Institute site).

Keywords: ISO 11929-1:2019, decision threshold, detection limit, coverage interval, ionizing radiation metrology, counting measurements, measurement uncertainty, Bayesian statistics, ISO/IEC Guide 98-3, UncertRadio.