3H

3H is a commonly used notation for tritium, the hydrogen-3 isotope. Tritium is an isotope of hydrogen with one proton and two neutrons, and it is radioactive. Its standard symbol is ³H, though 3H is also encountered in some texts. Tritium decays by beta emission to helium-3 with a half-life of about 12.32 years. It is produced in nuclear reactors and by neutron activation of lithium, and it occurs naturally in trace amounts in the atmosphere as a result of cosmic ray interactions.

Tritium has several practical applications. It is used in self-luminous devices, such as exit signs, watch dials, and gun sights, where its beta radiation excites phosphors to emit light without an external power source. In biochemical and environmental sciences, 3H-labeled (tritiated) compounds are used as tracers to study metabolic pathways and the fate of substances in organisms and ecosystems. In fusion research, tritium is a potential fuel component when paired with deuterium (D-T fusion), due to favorable reaction properties.

Safety and regulation are important considerations with 3H. As a radioactive substance, tritium can pose internal exposure risks if ingested or inhaled, though its low-energy beta particles limit external hazards. Sealed sources and proper containment minimize risk, and handling, transport, and disposal are governed by national and international regulatory frameworks.

In summary, 3H primarily denotes tritium, a radioactive hydrogen isotope with significant historical and contemporary use in lighting, tracing, and fusion research, while requiring appropriate safety and regulatory controls.