Towards new primary activity standardisation methods based on low-temperature detectors

Since the early 20th-Century, metrologists have supported the nuclear industry by providing primary radioactivity standardisation. Today, radioactivity measurements can reliably be delivered to just a few parts per thousand for most types of decay using standard instruments. However, for other types — specifically low-energy beta and electron capture decay — errors of several percent are typical, due to the low detection efficiency of low-energy decay and imprecise data analysis methods.

Low-temperature micro-calorimeters (LTDs), especially metallic magnetic calorimeters (MMCs), are widely considered as likely to offer value as universal tools for activity standardisation, due to characteristics of low-energy detection thresholds and applicability to all types of decay. To date, these devices have been custom-made, so unsuited to standardisation, an issue addressed in the EMPIR projects 15SIB10 MetroBeta and 17FUN02 MetroMMC that showed improved uncertainties and mitigated some inconsistencies in activity standardisation.

The second pillar of radionuclide metrology is the determination of nuclear decay data, typically by using theoretical models. Recent models consider underlying nuclear and atomic physics, but do not cover all types of decay and require experimental validation.

The project will develop a new primary activity standardisation method based on LTDs and improved fundamental nuclear decay data. Novel detectors with absorbers fully integrated into MMCs will be realised and reusable MMC detectors developed, as well as a new absolute method for activity standardisation based on MMCs. High-precision measurement of selected radioactive isotopes will be conducted to accurately determine decay data, for which modelling will be developed and validated.

Improved nuclear decay data by direct measurements and improved theoretical calculation techniques will support the adoption of LTD technologies, and provide a basis for international standards. Combined, these advancements will support the nuclear industry, such as for improving calculations of residual heat and processes within reactors, and waste management effectiveness.