Iridium (Iridium, Ir) is a chemical element of group VIII in Mendeleev's periodic system, belongs to the platinum metals, density of 22.5 g/cm3. High density and anti-corrosion properties allow to use iridium in alloys with platinum for the manufacture of surgical instruments. Artificially get isotope Ir192, which is the source of gamma radiation (see). The half-life of 74.4 day, gamma quantum energy of 0.4 MeV. Iridium is the first artificially radioactive isotope that was used for distant gamma therapy (see). Currently, for these purposes, iridium is not used because of the small half-life. Due to the high specific activity sources of Ir192 are very small, which allows to use them for interstitial irradiation (see Radiation therapy). Cm. also Isotopes (radioactive).