Tritium and less energetic neutrons (only fission, deuterium-tritium fusion, and splitting are net neutron producers), lithium deuteride is not used in boosted bombs, but rather for multi-stage hydrogen bombs. Tritium is an important fuel for controlled nuclear fusion in both magnetic confinement and inertial confinement fusion reactor designs. The experimental fusion reactor ITER and the National Ignition Facility (NIF) will use deuterium-tritium fuel. The deuterium-tritium reaction is favorable since it has the largest fusion cross-section (about 5.0 barns) and it reaches this maximum cross-section at the lowest energy (about 65 keV center-of-mass) of any potential fusion fuel. The Tritium Systems Test
Isotope geochemistry usually is given as a multiple of the present atmospheric ratio (Ra). Common values for R/Ra: He/He isotope chemistry is being used to date groundwaters, estimate groundwater flow rates, track water pollution, and provide insights into hydrothermal processes, igneous geology and ore genesis. U-series isotopes are unique amongst radiogenic isotopes because, being in the U-series decay chains, they are both radiogenic and radioactive. Because their abundances are normally quoted as activity ratios rather than atomic ratios, they are best considered separately from the other radiogenic isotope systems. Uranium is well mixed in the ocean, and its decay produces Pa and