Description
The radionuclide $^{163}$Ho, undergoing electron capture, has optimum properties to be used in experiments for the determination of the neutrino mass scale. This stems from its very low value $Q$-value, $Q_{\mathrm{EC}}$ ~ 2.83 keV which is very close to the binding energy of the 3s electrons. $Q_{\mathrm{EC}}$ is the maximum energy available for atomic excitations (assuming massless neutrinos), hence electrons from the K and L shells cannot be captured. Only one other nuclide, undergoing electron capture to the nuclear ground state of the daughter nucleus, has a $Q_{\mathrm{EC}}$ value which does not allow for K-captures, namely $^{193}$Pt. A high energy resolution calorimetric measurement of the $^{193}$Pt electron capture spectrum is of major importance to test the models for the description of low energy electron capture processes. We present a $^{193}$Pt spectrum obtained with low temperature metallic magnetic calorimeters with $^{193}$Pt ion-implanted in gold absorbers. We discuss the obtained results in comparison with the available high energy resolution $^{163}$Ho electron capture spectra.
