The discovery of neutrino oscillation proved recently that neutrinos have non-vanishing masses in contrast to their present description within the Standard Model of particle physics. However, the neutrino mass scale, which is very important for particle physics as well as for cosmology and astrophysics, cannot be resolved by oscillation experiments. The beta-decaying isotope tritium is a key isotope to search for new physics in the neutrino sector: For more than 50 years tritium has been the best isotope to search for a non-zero value of the mass of the neutrino.

The recent experiments at Mainz and Troitsk have given upper limits of about 2 eV/c2. The new Karlsruhe Tritium Neutrino Experiment (KATRIN) will enhance the sensitivity on the neutrino mass by another order of magnitude down to 0.2 eV/c2. KATRIN will use a windowless gaseous tritium source, in which the tritium inventory is re-circulated and purified yielding a column density of 5 1017 molecules/cm2.

Another way to search for new physics beyond the Standard Model of particle physics is to use tritium as a very strong source of low energy electron antineutrinos. The elastic cross section of low energy neutrinos on electrons allows the experiment to become sensitive to a possible magnetic moment of the neutrino.