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Working to increase knowledge of radionuclide decay data and to develop a new primary method for activity determination

Decay data, in particular beta spectra and electron capture probabilities of radionuclides used in industry, research and environmental applications, as well as for nuclear medicine, is not easy to determine. Since the early 20th-Century, radionuclide metrology has supported these beneficial uses by providing the basis for a traceability chain starting with primary activity standardisation. Radionuclide metrology, and more specifically, activity standardisation, is based on well-established measurement techniques that have been used and improved for decades. However, some radionuclides are especially challenging to standardise and achievable uncertainties are higher compared with others.

EMPIR project Towards new primary activity standardisation methods based on low-temperature detectors (PrimA-LTD, 20FUN04) is working to close this gap by developing new primary techniques for activity standardisation using low-temperature micro-calorimeters. The combination of high-resolution spectrometry for radioactive decays with sophisticated novel theoretical calculations of the spectrum shape will also increase knowledge of the fundamental decay data.

The project is developing a new primary activity standardisation method based on low-temperature micro-calorimeters and improved fundamental decay data. Low-temperature micro-calorimeters, especially metallic magnetic calorimeters, are widely considered as likely to offer value as tools to validate and improve established techniques for activity standardisation.

The determination of the maximum beta energy of ¹⁵¹Sm is a good example of a measurement result of the project with unprecedented uncertainty The maximum beta energy was found to be (76.430±0.068) keV. Compared to the previously adopted value in literature, the uncertainty has been reduced by more than a factor of 7. The shape of the beta spectrum has also been measured with unprecedented precision and forms the basis for precise activity determination by liquid scintillation counting and for a determination of the mean beta energy. Mean beta energies, like maximum beta energies, are very fundamental parameters and are needed, for example, to estimate the residual heat in nuclear waste.

This work was described in the paper High precision measurement of the ¹⁵¹Sm beta decay by means of a metallic magnetic calorimeter published in the journal Applied Radiation and Isotopes.

Project coordinator Ole Nähle from PTB said

‘Using low-temperature micro-calorimeters for absolute activity measurements is certainly one of the biggest challenges in radionuclide metrology and with this project we made a big step forward.’

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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