Tritium, represented by the symbol \(^3H\) or T, is a radioactive isotope of hydrogen. Unlike common hydrogen (protium), tritium’s nucleus contains one proton and two neutrons. This instability results in a radioactive half-life of approximately 12.32 years. Tritium is extremely scarce compared to protium and deuterium. Because of its short half-life, any primordial tritium that existed when the Earth formed has long since decayed, meaning its current presence in nature is a result of constant, low-level creation.
Natural Abundance and Formation
The trace amounts of tritium found naturally on Earth are continuously manufactured in the upper atmosphere. This process is driven by high-energy cosmic rays, which are streams of charged particles constantly bombarding the planet. When these cosmic rays collide with nitrogen and oxygen atoms, they cause nuclear reactions. A neutron-rich cosmic ray interacts with a nitrogen-14 atom, generating a proton and a tritium atom in a process called spallation.
The annual global production is estimated to be very low, only about 0.20 to 0.40 kilograms. Once formed, the tritium rapidly combines with oxygen to create tritiated water (HTO), which then mixes with the world’s oceans and freshwater sources through precipitation. The relatively short half-life means that roughly 5.5 percent of the existing natural supply decays into stable helium-3 every year. This constant decay balances the low production rate, maintaining an extremely low concentration of tritium in natural water relative to ordinary hydrogen.
Industrial Production and Controlled Supply
Natural sources of tritium are inadequate for the demands of modern technology, necessitating industrial production. The primary method for manufacturing tritium involves specialized nuclear fission reactors, which provide the necessary neutron flux. This artificial creation relies on irradiating targets containing the stable isotope lithium-6 with neutrons to initiate a nuclear reaction.
When a neutron strikes a lithium-6 nucleus, the atom splits, yielding a helium-4 atom and a tritium atom. Since the natural abundance of lithium-6 is low, the lithium must first be chemically enriched to a much higher concentration to efficiently produce tritium. This enrichment process adds significant cost and complexity to the supply chain.
After irradiation, the newly created tritium must be extracted and purified. The infrastructure required for this multi-step process is complex, costly, and limited to specialized, often government-controlled facilities. Since tritium constantly decays, stocks must be replenished regularly, and tight control over production limits its commercial availability, contributing to its high market price.
Key Applications Driving Demand
Tritium is valued for its unique physical properties, which enable several high-tech applications. Its low-energy beta radiation does not penetrate human skin, making it a safe component in self-powered lighting devices. Tritium gas is sealed in glass tubes coated with a phosphor material; the emitted electrons strike the phosphor, causing it to glow without any external power source. These radioluminescent devices, known as betalights, are used in watch faces, emergency exit signs, and specialized firearm sights.
A major application for tritium is in controlled nuclear fusion energy. Tritium, combined with deuterium, forms the most promising fuel mixture for first-generation fusion reactors, such as those employing the tokamak design. The deuterium-tritium reaction releases substantial energy, making it the focus of research aiming to develop a sustainable power source. Since fusion reactors require large, continuous supplies, scientists are developing methods for the reactor to breed its own fuel from a lithium blanket.
Tritium is also widely used in scientific research as a radioactive tracer. Because it is a form of hydrogen, tritium can substitute for protium in water molecules and organic compounds without significantly changing their chemical behavior. This allows researchers to track the movement of water in hydrological studies, such as tracing groundwater flows, and to label complex molecules in biomedical research. The ability to precisely follow the path of tritiated compounds provides a powerful tool for analyzing chemical reactions and biological metabolism.