Nuclear magnetic resonance of anti-parallel spin neutrons (of total spin zero for the neutron-spin pair), plus a proton of spin . Therefore, the tritium total nuclear spin value is again , just like for the simpler, abundant hydrogen isotope, H nucleus (the "proton"). The NMR absorption frequency for tritium is also similar to that of H. In many other cases of "non-radioactive" nuclei, the overall spin is also non-zero. For example, the nucleus has an overall spin value . A non-zero spin formula_2 is always associated with a non-zero magnetic dipole moment, formula_3, via the relation formula_4 where "γ" is the gyromagnetic ratio.
Tritium in nuclear reactors. Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. In the most important reaction for natural production, a fast neutron (which must have energy greater than 4.0 MeV) interacts with atmospheric nitrogen: Worldwide, the production of tritium from natural sources is 148 petabecquerels per year. The global equilibrium inventory of tritium created by natural sources remains approximately constant at 2,590 petabecquerels. This is due to a fixed production rate and losses proportional to the inventory. According to a 1996 report from Institute for Energy and Environmental Research on the US Department of Energy, only of