nnicaTritium
Tritium (three-hydrogen) is a radioactive isotope of hydrogen made up of one proton and two neutrons. Combined with deuterium, it is used as the fuel for the fusion reaction that is currently closest to being realized.
Simple Definition (High School)
Section titled “Simple Definition (High School)”Ordinary hydrogen has just one proton in its nucleus. Add one neutron and you get deuterium; add two neutrons and you get tritium. They all belong to the same hydrogen family, but the added weight makes each one a little heavier.
Because it is heavier, tritium is unstable, and over time it turns on its own into a different atom (helium-3). As it does so, it throws out a tiny particle (an electron), which is why it is treated as a radioactive material. Almost none of it exists naturally on Earth, so to use it in a fusion reactor we have to produce it artificially.
Precise Definition (Undergraduate and Above)
Section titled “Precise Definition (Undergraduate and Above)”Tritium (symbol or T) is a hydrogen isotope with mass number 3, whose nucleus consists of one proton and two neutrons. It has a half-life of about 12.3 years and decays into helium-3 through beta decay (β⁻ decay).
This equation shows that tritium emits an electron and an electron antineutrino as it becomes helium-3. The energy of the emitted beta rays is low, at most about 18.6 keV, enough to be stopped by a single sheet of paper or the outer layer of the skin. However, if it is taken into the body it can cause internal exposure, so its handling requires containment.
Apart from tiny amounts produced by the reaction of cosmic rays with the atmosphere, tritium is essentially absent in nature. Therefore, to use it as fuel for a fusion reactor, it must be produced (bred) artificially inside the reactor.
Role in Fusion Research
Section titled “Role in Fusion Research”The fusion reaction that is currently easiest to trigger is the D-T reaction, which uses deuterium (D) and tritium (T). When D and T fuse in a plasma at about 100 million degrees, they produce helium-4 and a neutron, releasing 17.6 MeV of energy. Because it achieves a high reaction rate at a lower temperature than other reactions, early fusion reactors are designed around the D-T reaction.
The problem is that tritium is almost nonexistent in nature and has a short half-life. That is why breeding tritium by striking lithium with neutrons inside the blanket surrounding the reactor is indispensable. Whether the reactor can produce more tritium than it consumes is the key to whether a D-T fusion reactor can operate self-sufficiently.