Hope that you liked the two isotopes of hydrogen that we have already presented. Otherwise, the third time’s a charm, because today’s nuclide is Hydrogen-3. Where hydrogen’s single proton is joined by two neutrons. It goes more commonly under the name tritium. For some reason, the isotopes of hydrogen got their own names and chemical acronyms (H, D, T), just as if they were their own elements.

Tritium is radioactive with 12 years half-life, and its abundance is therefore very low. It is created naturally by interactions of cosmic radiation in the atmosphere, and because of this continuous supply there is an equilibrium activity of tritium of about 100 PetaBequerel on Earth. However, there is also anthropogenic production, causing additional tritium to be around than what is caused by cosmic radiation alone. In particular, there was tritium released in atmospheric nuclear weapons tests during the last century, which is still remaining, and also there are some releases from the nuclear industry. Tritium is produced by fission reactors in the fuel, and also it is produced in neutron reactions with lithium, boron and heavy hydrogen (deuterium).

Because of its natural production, similar to that of carbon-14, tritium has also been suggested for radiodating. The much shorter half-life than the carbon would make it suitable for dating on a shorter time scale than the carbon. However, this is made complicated by the artificial tritium currently added since the forties.

Another common use of tritium is in radioluminescent paint, for example in emergency exit signs and wrist watches, just like you may remember from a few days ago that one used to do with radium-226. Tritium is much more practical to use for this purpose, and has replaced the radium, largely because the decay properties are more suitable. Tritium decays with a low energy beta decay to helium-3. There are no gamma rays associated with that decay, and the beta is easily stopped by a transparent layer outside the tritium paint. Tritium is therefore of less radiotoxic concern than radium. While tritium, being a hydrogen after all, is taken up by the body, it passes through our systems with a short biological half-life, and the low energy beta is harmless if the exposure is external.

It should also be said that tritium is also used in nuclear weapons. Because the principle of a fission nuclear weapon is relying on a very fast neutronic chain reaction, it is critical for its function that first neutrons appear in the right moment, and that subsequently neutrons are multiplying at a fast rate. Tritium can aid in achieving this, since it has fusion reactions that release neutrons. In addition, fusion weapons can have tritium fuel that is ignited by the primary fission bomb, thereby increasing the explosive yield of the weapon by the fusion of tritium and deuterium. However, lithium can also be used for this purpose, since it reacts with neutrons producing tritium, and lithium doesn’t decay away while stored, so therefore it may be the preferred choice.

A much more peaceful application of the tritium fusion must be mentioned as well: Thermonuclear fusion power is often seen as the holy grail of energy sources, and a way to bring the heating source of the sun down to our planet. However, it remains very difficult to get the fusion fuels hot enough to start burning (not literally burning in the sense of combustion with oxygen, but for the nuclei to fuse together while releasing energy). At the required temperatures, the material is in a plasma phase, meaning that the electrons are not bound anymore to the atoms. Containing the high temperature plasma for long enough durations is an engineering challenge, since it should not touch the walls of the container. One way to solve this is with powerful magnetic fields.

We have already mentioned that deuterium is possible to use as a fusion reactor fuel, and actually, the most promising fusion fuel to achieve ignition would be a mixture of deuterium and tritium. Deuterium, which is stable, can be isotopically enriched from water, while the tritium would be produced at the same rate as it’s consumed by neutronic production from lithium. The plan is to use neutrons, which are emitted from the fusion reactions, and let them hit a lithium breeding blanket. The tritium that is produced is saved for later use in the reactor.

In France, the international experimental reactor ITER is currently being assembled, and it will start operation with deuterium and tritium fuel plasma in the 2020-ies. The ITER collaboration started in the 1980-ies as an initiative for peaceful collaboration between the superpowers, by Gorbachev and Reagan.