When the use of ionizing radiation in science, medicine and industry first became widespread it was clear that a world-wide system would be required to assure accuracy in measurement. In 1960, the 11th General Conference decided to establish the Ionizing Radiation Section at the BIPM.

The principal activities of the BIPM in the field of ionizing radiation are to maintain the international reference standards for dosimetry and activity measurements. These standards are used in the BIPM key comparisons and their development and improvement is a major part of the research and development programme. The section also undertakes calibrations for national laboratories, and participates in international comparisons under the auspices of the CCRI.

Accurate measurements of the effects of ionizing radiation are required in a wide range of industrial and medical applications where they are critical in decisions relating to human health and safety. In the field of dosimetry for radiotherapy, the accuracy required for such measurements is set by the need to avoid errors greater than the smallest detectable physiological effect.

In the areas needing activity measurements, nuclear medicine is perhaps the most stringent in its accuracy requirements. Generally this means that the uncertainty of measurements in hospitals should not exceed a few percent.

The fact that the accuracy sought is modest compared with that required in many other areas of metrology should not disguise the formidable difficulties that must be overcome to achieve this level of accuracy.