Iridium-192 (symbol ¹⁹²Ir) is a radioactive isotope of iridium, with a half-life of 73.827 days.^[1] It decays by emitting beta (β) particles and gamma (γ) radiation. About 96% of ¹⁹²Ir decays occur via emission of β and γ radiation, leading to ¹⁹²Pt. Some of the β particles are captured by other ¹⁹²Ir nuclei, which are then converted to ¹⁹²Os. Electron capture is responsible for the remaining 4% of ¹⁹²Ir decays.^[2] Iridium-192 is normally produced by neutron activation of natural-abundance iridium metal.^[3] Iridium-192 is a very strong gamma ray emitter, with a gamma dose-constant of approximately 1.54 μSv·h⁻¹·MBq⁻¹ at 30 cm, and a specific activity of 341 TBq·g⁻¹ (9.22 kCi·g⁻¹).^[4][5] There are seven principal energy packets produced during its disintegration process ranging from just over 0.2 to about 0.6 MeV. It is commonly used as a gamma ray source in industrial radiography to locate flaws in metal components.^[6] It is also used in radiotherapy as a radiation source, in particular in brachytherapy. Iridium-192 has accounted for the majority of cases tracked by the U.S. Nuclear Regulatory Commission in which radioactive materials have gone missing in quantities large enough to make a dirty bomb.^[7]

The metastable isomer ^192m2Ir is iridium's most stable isomer. It decays by isomeric transition with a half-life of 241 years,^[8] which makes it unusual, both for its long half-life for an isomer, and that said half-life greatly exceeds that of the ground state of the same isotope.