Isotopes of 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 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.
List of isotopes
Use of radioisotopes
The isotope selenium-75 has radiopharmaceutical uses. For example, it is used in high-dose-rate endorectal brachytherapy, as an alternative to iridium-192.In paleobiogeochemistry, the ratio in amount of selenium-82 to selenium-76 can be used to track down the redox conditions on Earth during the Neoproterozoic era in order to gain a deeper understanding of the rapid oxygenation that trigger the emergence of complex organisms.