Beta spectrometry with metallic magnetic calorimeters

•The beta spectrum of 63Ni was measured with metallic magnetic calorimeters.•Dried sources are not adequate, electroplated sources yield accurate spectra.•The atomic exchange effect was confirmed down to very low energy (200 eV).

Metallic magnetic calorimeters are a specific type of cryogenic detectors that have been shown to enable precise measurement of the shape of low energy beta spectra. The aim of their use at LNHB is the determination of the shape factors of beta spectra. The beta source is enclosed in the detector absorber, allowing for very high detection efficiency. It has turned out that the type of source is of crucial importance for the correctness of the measured spectrum. Spectra of 63Ni measured with several sources prepared by drying a NiCl2 solution differ from one another and from theory, whereas spectra measured with electroplated sources are reproducible and agree with theory. With these latter measurements we could confirm the atomic exchange effect down to very low energy (200 eV).