185Re

185Re, or rhenium-185, is a stable isotope of the element rhenium (Re) with a mass number of 185. It is one of the two naturally occurring isotopes of rhenium; the other is 187Re, which is radioactive with a very long half-life.

Natural abundance of 185Re is about 37.4%, while 187Re accounts for about 62.6%. The presence of both isotopes gives natural rhenium an atomic weight of roughly 186.2 u. 185Re is stable and does not decay, whereas 187Re is radioactive and decays to 187Os with a half-life on the order of 10^10 years. The 187Re–187Os decay system is used in geochronology and cosmochemistry for dating geological and planetary materials.

Occurrence and production: Rhenium is a rare element that occurs in minute quantities in various minerals, most notably in molybdenite (MoS2) and related ore deposits. In nature, rhenium is found as a mixture of isotopes, with 185Re and 187Re being the predominant ones. Industrially, rhenium is recovered as a byproduct from molybdenum and copper ore processing, and it is refined for use in specialized alloys and catalysts.

Applications: Rhenium is valued for high-temperature strength and creep resistance, and is commonly added to nickel-based superalloys and certain tungsten-based alloys used in aerospace and other demanding applications. Although 185Re itself is stable, the presence and ratio of rhenium isotopes influence material properties and isotopic studies. The 187Re isotope enables the Re–Os dating technique, while 185Re serves as part of the natural isotopic mix studied in geochemistry and materials science.