iridium191

Iridium-191 is a stable isotope of the chemical element iridium (atomic number 77). It has a mass number of 191 and is one of the two stable isotopes that occur naturally in iridium, the other being 193Ir.

In natural iridium, 191Ir accounts for about 37 percent of the element, with 193Ir making up the remainder, around 63 percent; these values are approximate and may vary slightly between samples.

Because 191Ir is stable, it does not undergo radioactive decay and has no measured half-life.

Iridium is a rare, dense metal found in nickel–iron meteorites and in trace amounts in the Earth's crust; the 191Ir isotope contributes to the natural isotopic composition used in geochemical and cosmochemical studies to trace sources and processes involving iridium.

Industrial applications focus on other iridium isotopes, particularly 192Ir, which is radioactive and used in radiography and cancer therapy; 191Ir itself is not used for radioactive sources.

See also: Isotopes of iridium.