A guidance document on the assessment of measurement uncertainty will also benefit SSDLs that signed the Mutual Recognition Arrangement (MRA) of National Measurement Standards and of the Calibration and Measurement certificates Issued by the National Metrology Institutes. The IAEA signed the MRA in October 1999 and has, since then, contributed to strengthening the SSDL capabilities in this field. The signing by the IAEA of the MRA imposes stricter demands on its dosimetry comparisons and may require a modification of the criteria of acceptability of the level of performance achieved by SSDLs in these comparisons.
A common procedure for uncertainty assessment among all SSDL Network members would greatly facilitate the review of comparison results by the IAEA and other regional or international institutions.
The purpose of this publication is to provide guidance to SSDLs on how to assess and report measurement uncertainty related to their calibration services in a way that is consistent with the GUM. It includes a review of the calibration procedures and model equations used by SSDLs in Section 2, a tutorial part on how to assess the various uncertainty components in Section 3, and two practical examples of typical calibrations in 60Co gamma ray beams. The practical examples, linked to the concepts described in Sections 2 and 3, are given to help the user in preparing the uncertainty budget. Although the scope of this publication is limited to a model equation used in 60Co gamma beam for radiotherapy dosimetry, the concept can be extended to cover X ray dosimetry for radiotherapy and radiation protection dosimetry. For the calibration of instruments used in diagnostic radiology, the guidance given in IAEA technical Reports Series No. 457  should be followed.