Isotopes of selenium

Selenium has six natural isotopes that occur in significant quantities, along with the trace isotope ⁷⁹Se, which occurs in minute quantities in uranium ores. Five of these isotopes are stable: ⁷⁴Se, ⁷⁶Se, ⁷⁷Se, ⁷⁸Se, and ⁸⁰Se. The last three also occur as fission products, along with ⁷⁹Se, which has a half-life about 330,000 years, and ⁸²Se, which has the very long half-life of 8.76×10¹⁹ years as it decays via double beta decay to krypton-82 and for practical purposes can be considered to be stable. There are 23 other unstable isotopes that have been characterized, the longest-lived after ⁷⁹Se being ⁷⁵Se with its half-life 119.78 days, ⁷²Se at 8.40 days, and ⁷³Se at 7.15 hours. The others are all under an hour and most do not exceed 38 seconds.