Limits on Neutrino-Mixing from the Internal Bremsstrahlung Spectrum of I-125

Abstract

The massive antineutrino recently reported by Simpson in an experiment on tritium decay has not been confirmed by experiments on S-35 decay. As an independent check, we report here the negative result of a search for the corresponding antiparticle (a massive neutrino) using the decay of I-125. As a by-product, we give accurate data on internal-bremsstrahlung spectra which we have followed over close to four decades in intensity, and we report a new way of measuring its E1/M1 ratio. The experiment provides a new and very accurate value for the I-125-Te-125 mass difference of 186.1 ± 0.3 keV.