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Results from a completed EMPIR project will have impact in the nuclear industry and laboratories around the world measuring radioactive material

The project

For decommissioning nuclear plants, it is important to know how much radioactive material remains in the core to direct the decontamination and disposal of radioactive waste.

When nuclear waste decays it releases in general three types of radiation: beta minus (β-) electrons, gamma-rays and anti-neutrinos. These are released with varying amounts of energy depending on the exact nature of the radioactive material (or radionuclide). If the energy spectra are added together, then this gives the value of the ‘decay heat’ which is important to calculate how much fissionable material is present and how much cooling is required.
However, there is often a minor difference obtained between measurements and calculations – in other words the beta and gamma signals do not sum up to completely give the decay heat. This is due to inaccuracies in the modelling process of beta decay in the calculations, which often have large uncertainties.

A project within EURAMET’s European Metrology Programme for Innovation and Research (EMPIR), Metrology for the accurate measurement of radionuclide beta spectra (MetroBeta, 15SIB10), developed theoretical and experimental approaches to measure the spectra of beta radiation to an unprecedented level of accuracy, including modelling the shape of the spectra for the first time. From this work the LNE-LNHB the National Metrology Institute (NMI) of France for ionising radiation who coordinated the project, improved their beta code software used to calculate beta spectra and further developed their cryogenic detection system, used to measure these spectra.

Uptake of project outputs

Data from the new beta code have been used to provide beta spectra for two major international nuclear decay data evaluation projects:

• The International Atomic Energy Agency’s (IAEA) International Network of Nuclear Structure and Decay Data Evaluators (NSDD) for use in their Evaluated Nuclear Structure Data File (ENSDF)
• The Decay Data Evaluation Project (DDEP), which provides decay scheme data mainly to the metrology community.

It is also anticipated that the code will be used in:

• The Joint Evaluated Fission and Fusion (JEFF) project of the OECD Nuclear Energy Agency which will use project data from the new code when JEFF is next updated around 2023. This project produces the basic data files used by the European nuclear industry for their nuclear reactor calculations.
• National Metrology Institutes to calculate the correct shape of beta spectra required for primary activity measurements.
• Nuclear medical centres for improved dose predictions.

Beta spectra are important in many other applications as well as the nuclear industry – such as in the measurements made by liquid scintillation counters. The LNE-LNHB and project partner PTB, the NMI of Germany, compared the activity of radioactive samples at different laboratories as measured by liquid scintillation counters and found inconsistencies in the results. This was not due to errors in the methodology, but due to the data processing step, where calculations of the beta spectra are used in the analysis of the results from the counter used to measure beta electron activity. This is a profound result as such counters are a common instrument in laboratories around the world.

Good practice guides

The project has released four good practice guides for making improved beta spectra measurements which are available for download from the project’s website as well as the updated BetaShape software for windows, MacOS and Linux, available from the LNE-LNHB website.

• Beta spectra measurement using magnetic spectrometer
• Beta spectra measurement using Si(Li) detectors
• Measurement of beta spectra using solid scintillator crystals
• The use and development of magnetic metallic calorimeters

Project results were already used in the EMPIR project:

• Metrology for clinical implementation of dosimetry in molecular radiotherapy  (MRTDosimetry, 15HLT06)

and are now being used in another EMPIR project:

• Measurement of fundamental nuclear decay data using metallic magnetic calorimeters (MetroMMC, 17FUN02)

Work on improving still further nuclear decay calculations and measurements will continue in a new EMPIR follow on project, Towards new primary activity standardisation methods based on low-temperature detectors (PrimA-LTD, 20FUN04) which started on the 1st June 2021.

Mark Kellett, who coordinated the project said about the work:

“The novel use and development of cutting edge cryogenic detectors, coupled with theoretical advances in the field of beta spectra, have allowed our fundamental understanding of this important decay phenomenon to make a significant leap forward. The impact on both the treatment of radioactive waste from the nuclear power industry, and patients in the nuclear medicine sector, will help improve the well-being of society for years to come.”

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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