76Ge

Germanium-76 (76Ge) is an isotope of the element germanium with atomic number 32 and a mass number of 76. Its nucleus contains 32 protons and 44 neutrons. The ground-state spin and parity are 0+. It is one of the naturally occurring germanium isotopes, with a natural abundance of about 7.8% in terrestrial germanium.

76Ge is conventionally considered stable, as it does not undergo single beta decay. However, it can, in principle, participate in double beta decay to selenium-76 (76Se). The two-neutrino double beta decay mode has been observed and has a half-life on the order of 10^21 years. The energy release (Q-value) for the decay to 76Se is about 2,039 keV.

Because of its chemical properties and the high energy resolution of germanium detectors, 76Ge is widely used in experiments searching for neutrinoless double beta decay. These experiments rely on enriched germanium detectors with a large fraction of 76Ge, typically around 86–88%. Notable programs include the Heidelberg-Moscow, IGEX, GERDA, and Majorana Demonstrator projects, with LEGEND under development to increase sensitivity.

By measuring or constraining neutrinoless double beta decay, researchers aim to determine whether neutrinos are Majorana particles and to place limits on the effective neutrino mass. The detection of such decay would have implications for particle physics and cosmology.