– the intergovernmental organization through which Member States act together
     on matters related to measurement science and measurement standards.
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For x-rays and gamma-rays, the BIPM maintains primary standards of air kerma and absorbed dose that have excellent long-term stability and carefully evaluated uncertainties and so are used as international reference standards. By means of regular international comparisons a stable, reliable world-wide network of standards is maintained.

This provides confidence in radiation measurements, especially those used for patient dosimetry as well as staff radiation doses received during the medical use of x-rays, for example during interventional radiology that is shown in the picture on the right.

For those national laboratories that do not have their own primary standards, BIPM characterizations/calibrations are available.

medium-energy x-rays in diagnostic radiology
linear accelerator
Courtesy of Department of Radiation Oncology, Stanford Comprehensive Cancer Center, USA

As the number of linear accelerators worldwide is increasing rapidly because they are the tool of choice for radiation beams used to treat cancer, the BIPM, in consultation with the Consultative Committee for Ionizing Radiation (CCRI), has developed a primary standard graphite calorimeter that travels around the world for international comparisons of accelerator dosimetry. The results are being added to the KCDB as they are published.