Fig. (19) A Monte Carlo simulation of the calorimetric spectrum of the 163Ho electron capture decay [151]. Calculations were based on the following assumptions: a decay energy QEC = 2200 eV, a neutrino mass mν = 0, a total number of decay events Nev = 1014, a microcalorimeter energy resolution ΔEFWHM = 2 eV and a pile-up fraction fpp = 10-6. The bottom curve is a fit of the pile-up spectrum. The insert shows the uppermost part of the spectrum depending on the neutrino mass in a similar way as in the case of the β-ray spectra. Note the complexity of the pile-up spectrum at the end of the 163Ho decay spectrum.