Limit on Lepton Nonconservation and Neutrino Mass from Double Beta Decay

A lower limit of 5×{}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 was only 2×{}10^-3 count/keV·{}h total at the expected 2.041-MeV peak.