The accurate measurement of radioactivity is essential for applications of ionizing radiation such as medical imaging, cancer therapy and environmental protection. To ensure that such measurements are harmonized world-wide, the BIPM operates a set of very stable and precise instruments to compare national standards of radioactivity. Up till now it has been possible to compare standards of radionuclides that emit gamma rays; setting up an equivalent instrument for radionuclides that only emit beta rays has proved to be a technical challenge. Scientists from the BIPM have worked closely with colleagues from national metrology institutes in Germany, France, Poland, China and the UK to develop a new instrument; the device combines signals from three detectors surrounding a sample of the radioactive standard to determine an accurately reproducible parameter that is proportional to the activity (Bq) of the sample. The method was inspired by one of the techniques used to realize primary standards of radioactivity ('Triple-to-double coincidence counting'). Details have been published in Metrologia.

The new instrument, known as the ESIR, will enable metrology institutes to compare primary standards of pure beta-emitting radionuclides, reducing the need for complex and time-consuming multi-centre comparison exercises.

Contact Romain Coulon for more information.