Tritium-helium-3 tracing

While a deuterium-tritium (D-T) mix is the fuel of choice for sustained fusion research, tritium on Earth is scarce. Produced by cosmic ray protons colliding with nitrogen in the upper atmosphere, trace amounts are found in air and less abundantly in water.That is where lithium comes in. Bombarding lithium 6 or lithium 7 atoms with high-energy neutrons results in atoms of tritium and helium. 

Swelling can also result from gases produced in materials, such as helium formed by (n,a) reactions and other gaseous impurities present in the metals. These traces of gas increase the concentration of voids formed upon exposure to radiation. For example, the (n,a) and (n,2n) reactions between fast neutrons and beryllium form helium and tritium gases that create swelling. 

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