Iridium-192
Iridium-192 is a radioactive isotope of iridium, with a half-life of 73.82 days. It decays by emitting beta particles and gamma radiation. 95.24% of 192Ir decays occur via β- emission, leading to 192Pt; the remaining 4.76% occur via electron capture to 192Os; both modes involve gamma emission. Iridium-192 is normally produced by neutron activation of natural-abundance iridium metal. Iridium-192 is a very strong gamma ray emitter, with a gamma dose constant of 1.54 μSv·h−1·MBq−1 at 30 cm, and a specific activity of 341 TBq·g−1. There are seven principal gamma rays produced in its beta-minus decay, ranging from 296.0 to 612.5 keV, and two produced in its electron capture decay at 205.8 and 484.6 keV. It is commonly used as a gamma ray source in industrial radiography to locate flaws in metal components. 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.
The metastable isomer 192m2Ir is iridium's most stable isomer. It decays solely by isomeric transition with a half-life of 241 years, which is somewhat unusual for its long half-life and that said half-life greatly exceeds that of the ground state.