Beta spectrometry with metallic magnetic calorimeters in the framework of the European EMPIR project MetroBeta

The aim of the European Metrology Research Project MetroBeta is to improve the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The precise knowledge of beta spectra is required for the activity standardisation of pure beta emitters. Metallic magnetic calorimeters (MMCs), a type of cryogenic detectors, with the beta emitter embedded in the absorber have proven to be among the best beta spectrometers, in particular for low-energy beta transitions. Within this project, new designs of MMCs optimized for five different beta energy ranges were developed and a new detector module was constructed. The beta spectra of ¹⁵¹Sm, ¹⁴C and ⁹⁹Tc have been measured so far; additional measurements with ³⁶Cl are under preparation. Improved theoretical calculation methods and complementary measurement techniques complete the project.