Double beta decay, the tellurium-xenon systems and the electron associated neutrino mass

The features of double beta decay, common to many even-even nuclei are discussed in the light of a non-vanishing (Majorana) neutrino mass (matrix). The latter is considered to be the only lepton number violating effect perceptible at mass scales of a few MeV, characteristic for 2βsup(+-) decays. Estimates of the nuclear matrix elements mediating 2β-, 2anti ν and 2β-, 0anti ν final states are confronted with the relative rate of the 128Te → 128Xe and 130Te → 130Xe transitions. (orig.)