On the Q-values of the tritium beta-decay and the double beta-decay of 76Ge

The Q-values of the tritium beta-decay and the double beta-decay of Ge-76 are important parameters in determinations of neutrino properties, which still are open questions. The Q-value of the tritium beta decay determined from atomic masses may be used for improved future efforts to find a finite mass of the electron neutrino. The Q-value of the double beta-decay of Ge-76 to Se-76 gives the position of the monochromatic peak of charged particles expected in a neutrino-less decay mode, which if observed would show that the electron neutrino is a Majorana particle. Both these Q-values are related to experiments searching for violations of the standard model for weak interaction. The Q-values of the tritium beta-decay and the double beta-decay of Ge-76 were determined by using the Penning trap mass spectrometer SMILETRAP at the Manne Siegbahn Laboratory by measuring the masses of H-3, He-3, Ge-76 and Se-76, which were obtained from the cyclotron frequencies of H-3(+), He-3(2+), Ge-76(22,23+) and Se-76(24,25+) respectively, using H-2(+) as mass reference. The atomic masses involved were determined at an uncertainty of about 1 ppb. However, the Q-values are mass differences in which systematic uncertainties are reduced. The atomic masses of H-3 and He-3 determined this way are 3.016 049 278 4(10) u and 3.016 029 323 5(28) u respectively corresponding to a Q-value of 18.588(3) eV. The masses of Ge-76 and Se-76 are 75.921 402 758(96) u and 75.918 213 795(81) u respectively giving a Q-value of 2039.006(50)eV for the double beta decay.