Limit on lepton nonconservation and neutrino mass from double beta decay

A lower limit of 5 x 1022 yr (68% confidence level) has been obtained for the half-life of the neutrinoless double beta decay of 76Ge. This process would require lepton-number nonconservation and that the electron neutrino have a mass and/or the weak interaction have right-handed currents. Ge detectors of 178 and 158 cm3 were used inside a NaI active shield for 1618 h. The radioactivity background was kept so low that, despite operating above ground, there were only 2 x 10-3 counts/keVxh total at the expected 2.041-MeV peak