Precision Measurements of Beta Spectra using Metallic Magnetic Calorimeters within the European Metrology Research Project MetroBeta

MetroBeta, a recently completed European Metrology Research Project, aimed at the improvement of the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The most prominent experimental work package concerned the measurement of the spectrum shapes of several beta decaying radionuclides by means of metallic magnetic calorimeters (MMCs) with the beta emitter embedded in the absorber. New MMC chips were designed and optimized for five different absorber heat capacities, enabling the measurement of beta spectra with Q values ranging from few tens of keV up to ~ 1 MeV. Several beta spectra were measured with high energy resolution and statistics of up to 10 7 counts.