Tritium is the radioactive isotope of the element hydrogen. It has many useful applications.
Tritium is also known as hydrogen-3 and has an element symbol T or 3H. The nucleus of a tritium atom is called a triton and consists of three particles: one proton and two neutrons. The word tritium comes from Greek the word “tritos”, which means “third”. The other two isotopes of hydrogen are protium (most common form) and deuterium.
Tritium has an atomic number of 1, like other hydrogen isotopes, but it has a mass of about 3 (3.016).
Tritium decays via beta particle emission, with a half-life of 12.3 years. The beta decay releases 18 keV of energy, where tritium decays into helium-3 and a beta particle. As the neutron changes into a proton, the hydrogen changes into helium. This is an example of the natural transmutation of one element into another.
Ernest Rutherford was the first person to produce tritium. Rutherford, Mark Oliphant, and Paul Harteck prepared tritium from deuterium in 1934 but were unable to isolate it. Luis Alvarez and Robert Cornog realized tritium was radioactive and successfully isolated the element.
Trace amounts of tritium occur naturally on Earth when cosmic rays interact with the atmosphere. Most tritium that is available is made via neutron activation of lithium-6 in a nuclear reactor. Tritium is also produced by nuclear fission of uranium-235, uranium-233, and polonium-239. In the United States, tritium is produced at a nuclear facility in Savannah, Georgia. At the time of a report issued in 1996, only 225 kilograms of tritium had been produced in the United States.
Tritium can exist as an odorless and colorless gas, like ordinary hydrogen, but the element is mainly found in liquid form as part of tritiated water or T2O, a form of heavy water.
A tritium atom has the same +1 net electrical charge as any other hydrogen atom, but tritium behaves differently from the other isotopes in chemical reactions because the neutrons produce a stronger attractive nuclear force when another atom is brought close. Consequently, tritium is better able to fuse with lighter atoms to form heavier ones.
External exposure to tritium gas or tritiated water is not very dangerous because tritium emits such a low energy beta particle that the radiation cannot penetrate the skin. Tritium does pose some health risks if it is ingested, inhaled, or enters the body through an open wound or injection. The biological half-life ranges from around 7 to 14 days, so bioaccumulation of tritium is not a significant concern. Because beta particles are a form of ionizing radiation, the expected health effect from internal exposure to tritium would be an elevated risk of developing cancer.
Tritium has many uses, including self-powered lighting, as a component in nuclear weapons, as a radioactive label in chemistry lab work, as a tracer for biological and environmental studies, and for controlled nuclear fusion.
High levels of tritium were released into the environment from nuclear weapons testing in the 1950s and 1960s. Prior to the tests, it is estimated only 3 to 4 kilograms of tritium was present on the Earth’s surface. After testing, the levels rose 200% to 300%. Much of this tritium combined with oxygen to form tritiated water. One interesting consequence is that the tritiated water could be traced and used as a tool to monitor the hydrologic cycle and to map ocean currents.