4.1 Standards such as ISO 11137-1 (radiation sterilization of health care products) and ISO 14470 (irradiation of food) contain requirements that dosimetry used in the development, validation, and routine control of the process shall have measurement traceability to national or international standards and shall have a known level of uncertainty. The magnitude of the measurement uncertainty is important for assessing the results of the measurement system.

4.1.1 This guide provides information on how to meet the fundamental requirement to determine a known level of uncertainty associated with a dose measurement, how to calculate the overall uncertainty, and how the uncertainty may differ depending on the application (e.g., OQ and PQ dose measurements, routine dose measurement, determination of minimum absorbed dose (D_min) or maximum absorbed dose (D_max) from the monitoring location dose (D_mon)). Information is provided on how to identify and calculate different components of uncertainty used to establish an uncertainty budget.

4.2 Information on the range of achievable uncertainty values for specific dosimetry systems is given in the ISO/ASTM standards for the specific dosimetry systems. While the uncertainty values given in specific dosimetry standards are achievable, it should be noted that both smaller and larger uncertainty values might be obtained depending on measurement conditions and instrumentation. For more information, see also ISO/ASTM 52628.

4.3 This guide uses the methodology adopted by the GUM for estimating uncertainties in measurements (see 2.4). Therefore, components of uncertainty are evaluated as either Type A uncertainty or Type B uncertainty.

4.3.1 Quantifying individual components of uncertainty may assist the user in identifying actions to reduce the combined measurement uncertainty.

4.4 Although this guide provides a framework for assessing uncertainty, it cannot substitute for critical thinking, intellectual honesty, and experience. The evaluation of uncertainty depends on detailed knowledge of the nature of the measurand and of the measurement method and procedure used. The utility of the uncertainty quoted for the result of a measurement therefore ultimately depends on the understanding, critical analysis, and integrity of those who contribute to the assignment of its value (GUM 3.4.8 JCGM 100:2008).

1.1 This standard provides guidance on the use of concepts described in the JCGM (Joint Committee for Guides in Metrology) Evaluation of Measurement Data – Guide to the Expression of Uncertainty in Measurement (GUM) to estimate the uncertainties in the measurement of absorbed dose in radiation processing.

1.2 Methods are given for identifying, evaluating, and estimating the components of measurement uncertainty associated with the use of dosimetry systems, and for calculating combined standard measurement uncertainty and expanded uncertainty of dose measurements based on the GUM methodology.

1.3 Examples are given on how to develop a measurement uncertainty budget and a statement of uncertainty.

1.3.1 Key components of uncertainty are derived as part of the derivation of the uncertainty budget. This standard identifies which components of uncertainty are carried forward as part of other analyses (e.g., assessment of process capability and process targets, and process variability), and which components from other standards are brought forward into this standard (e.g., precision of the dose measurement, calibration curve fit, and indirect measurement of dose).

1.4 This document is one of a set of standards that provides recommendations for properly implementing dosimetry in radiation processing, and provides guidance for achieving compliance with the requirements of ISO 11137-1 (radiation sterilization of health care products), ISO 14470 (treatment of food), and ISO/ASTM 52628 related to the evaluation and documentation of the uncertainties associated with measurements made with a dosimetry system. It is intended to be read in conjunction with ISO/ASTM 52628 (Standard Practice for Dosimetry in Radiation Processing), and ISO/ASTM 51261 (Practice for Calibration of Routine Dosimetry Systems for Radiation Processing).

1.5 To achieve compliance with the requirements of ISO 11137-1 (radiation sterilization of health care products), ISO 14470 (treatment of food), and other applications, a measurement is accompanied by a statement of the uncertainty.

1.6 This guide does not address the establishment of process specifications or conformity assessment.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.