The calorimetric spectrum of the electron-capture decay of 163 Ho. the spectral endpoint region

The electron-neutrino mass (or masses and mixing angles) be directly measurable in weak electron-capture decays. the favoured experimental technique is “calorimetric”. the optimal nuclide is 163ho, and several experiments (echo, holmes and numecs) are currently studying its decay. the most relevant range of the calorimetric-energy spectrum extends for the last few hundred ev below its endpoint. it has not yet been well measured. we explore the theory, mainly in the cited range, of electron capture in 163ho decay. a so far neglected process turns out to be most relevant: electron-capture accompanied by the shake-off of a second electron. our two main conclusions are very encouraging: the counting rate close to the endpoint be more than an order of magnitude larger than previously expected; the “pile-up” problem be significantly reduced.