Searching for active and sterile neutrinos in beta-ray spectra

The oscillation experiments proved that neutrinos are massive particles: it holds mi ≠ 0 for at least two of their mass states and mi > 0.05 eV for at least one of these states. β-ray spectroscopy should be able to provide the values of mi themselves assuming that the β-spectra are measured with sufficient resolution and luminosity. Until now, only the upper limit of the effective mass of the electron neutrino m(νe)