ABSTRACT
A nuclear decay which is extremely important for neutrino physics is neutrinoless double β-decay. This lepton-number-violating process requires, in addition to a non-vanishing neutrino mass, that neutrinos are Majorana particles. Double β-decay is characterized by a nuclear process changing the nuclear charge Z by two units while leaving the atomic mass A unchanged. It is a transition among isobaric isotopes. mass from double β-decay is valid only for Majorana neutrinos, while β-decay is not sensitive on the character of the neutrino. Hence, both measurements deliver quite complementary information. Typical energies for double β-decay are in the region of a few MeV distributed among the two (or four, depending on the channel) leptons which are emitted as s-waves. Some double β-decay isotopes can be used in as solid or loaded liquid scintillators. Double β-decay is unique in a sense for having these additional Majorana phases.
