Tritium is a radioactive isotope of hydrogen, symbolized as T or ³H. It contains one proton and two neutrons in its nucleus, making it heavier than regular hydrogen. Tritium is produced naturally in the atmosphere when cosmic rays interact with nitrogen, but it can also be generated in nuclear reactors. Tritium is used in various applications, including nuclear fusion research and self-luminous devices like exit signs and watch dials. Its radioactive decay emits beta particles, which have a very low penetration ability, making tritium relatively safe to handle in controlled environments.