Ir191

Iridium-191 (191Ir) is a stable, non-radioactive isotope of the element iridium (atomic number 77). It has a mass number of 191 and is one of the naturally occurring isotopes of iridium, the other being 193Ir. In natural iridium, about 37% of the atoms are 191Ir, with the remainder mainly consisting of 193Ir.

Nuclear properties: 191Ir contains 114 neutrons (A − Z = 191 − 77 = 114). It is stable, with no radioactive decay and an effectively infinite half-life under normal conditions. Detailed nuclear spin and parity values are recorded in specialised databases but are not required for general descriptions.

Occurrence and production: 191Ir occurs naturally in trace amounts in Earth's crust as part of iridium-bearing minerals, typically alongside other platinum-group elements. Like the other stable iridium isotopes, it has existed since the formation of the Solar System. Commercial production focuses on refining platinum-group metal ores to obtain iridium metal and its compounds, from which isotopic compositions are measured or utilized.

Applications: Because 191Ir is stable, it is not used as a radiological source. Its isotopic abundance is relevant for geochemical and materials studies; stable‑isotope ratios involving 191Ir/193Ir can be used as tracers in isotopic analyses and for quality control in iridium metallurgy.

Safety: Being stable, 191Ir does not present radiological hazards. However, iridium compounds can be toxic if ingested or inhaled, so standard laboratory safety precautions apply when handling iridium materials.