section_path: Characteristics/Isotopes and stellar origin
section_name: Isotopes and stellar origin
paragraph_text: Isotopes and stellar origin
  
  Naturally occurring oxygen is composed of three stable isotopes, O, O, and O, with O being the most abundant (99.762% natural abundance).
  
  Most O is synthesized at the end of the helium fusion process in massive stars but some is made in the neon burning process. O is primarily made by the burning of hydrogen into helium during the CNO cycle, making it a common isotope in the hydrogen burning zones of stars. Most O is produced when N (made abundant from CNO burning) captures a He nucleus, making O common in the helium-rich zones of evolved, massive stars.
  
  Fifteen radioisotopes have been characterized, ranging from O to O. The most stable are O with a half-life of 122.24 seconds and O with a half-life of 70.606 seconds. All of the remaining radioactive isotopes have half-lives that are less than 27 seconds and the majority of these have half-lives that are less than 83 milliseconds. The most common decay mode of the isotopes lighter than O is β decay to yield nitrogen, and the most common mode for the isotopes heavier than O is beta decay to yield fluorine.