The Beta-Spectrum of Tritium and the Mass of the Neutrino

A direct determination of the beta-spectrum of H³ has been made in a high resolution magnetic spectrometer. The experimental data are fitted by a straight line Fermi plot from 5.5 kev to the maximum energy at 17.95±{}0.10 kev. An upper limit of 250 volts or 0.05 percent of the mass of the electron is obtained for the rest mass of the neutrino. New estimates are obtained for the H³ comparative half-life, the neutron half-life, and the value of the Fermi universal constant of beta-decay.