Metrology — Achieving Accurate and Consistent Absorbed Dose Measurement. Chapter 3

Any measurement of a quantity that plays a critical role in a process needs to be controlled by the international system of measurement [3.1]. This system means that there exists a traceable path that establishes the measurement as agreeing with the most accurate possible measurement using an internationally validated primary standard, within a known margin of uncertainty. Such agreement ensures universal comparability and is often a legal requirement. A primary standard is an instrument or material of the highest metrological quality that permits determination of the unit of a quantity from its definition, which has been verified internationally by comparison with the equivalent standards of different institutions at the same level. Many countries have a national standardizing laboratory designated by the government for the purpose of developing, maintaining and improving primary standards in radiation measurement. The Bureau International des Poids et Mesures (BIPM) was set up by the Metre Convention (originally signed in 1875, with 59 Member States and 42 Associate States and Economies as of 14 November 2018 [3.1]) as the international centre for metrology, with its laboratory and offices in Sèvres (France), in order to ensure worldwide uniformity on matters relating to metrology. Part of its role is to promote and advance the global comparability of measurements and to coordinate international comparisons of national measurement standards agreed to be of the highest priority.