Tritium

Discovered in 1934 by Ernest Rutherford, ML Oliphant and Paul Harteck, tritium (T, or H3) is the third isotope of hydrogen (H, or H1) alongside of deuterium (D, or H2).

Although tritium (also known as superheavy hydrogen) is a natural isotope, it is manily manufactured for industrial purposes.
Tritium has two neutrons in its atom core in addition to one proton (just like hydrogen). It is unstable and disintegrates whilst sending out beta radiation (electrons) with a half-life time of 12,3 years.
During this transition, each atom emits just one electron which leaves the core with a maximum energy of approx 18 KeV. This energy is very low compared with other radioactive isotopes.
Thus for example, the electron is unable to penetrate the human skin and can be stopped without any problems by a sheet of paper. Under standard condition, a milliliter (ml) tritium gas has an activity of approx. 2,588 Ci [Curie] or 94 GBq [Giga-Becquerel]. Further physical and chemical characteristics of tritium are almost identical to those of hydrogen. Like hydrogen, tritium oxidizes when exposed to oxygen. Doing so with tritium, results in tritiated water (HTO). The tritium gas is tasteless, odourless and considerably lighter than air. If tritium enters the body, it spreads evenly in the body water and is then again eliminated with a biological half-life time of 10 days.