Tritium (T, or N3) - radioactive isotope of hydrogen with mass number 3. The nucleus of tritium consists of 1 protons and 2 neutrons. Tritium can be obtained on the accelerator (see Accelerators of charged particles), bombarding neutrons or deuterons atoms of heavy hydrogen, lithium, beryllium. The half-life of tritium - 12.4 years. Tritium has a very soft beta radiation (see), which is fully absorbed by a layer of 5.7 mm air or 6.5 MK tissue. In nature tritium is constantly formed from nitrogen in the air under the action of cosmic rays (see Cosmic radiation). Throughout the earth's atmosphere contains 18 g and in the water of the oceans - about 800 Tritium can serve as a radioactive label for the study of synthesis and degradation of the DNA in the cell. It is used in thermonuclear bombs. Maximum allowable content of tritium in the human body - 2000 mccoury. Cm. also Isotopes.