Isotopes and stellar origin

Isotopes and stellar origin
Main article: Isotopes of oxygen
A concentric-sphere diagram, showing, from the core to the outer shell, iron, silicon, oxygen, neon, carbon, helium and hydrogen layers.
Late in a massive star's life, 16O concentrates in the O-shell, 17O in the H-shell and oxygen-1818O in the He-shell.

Naturally occurring oxygen is composed of three stable isotopes, 16O, 17O, and 18O, with 16O being the most abundant (99.762% natural abundance).[31]

Most 16O is synthesized at the end of the helium fusion process in massive stars but some is made in the neon burning process.[32] 17O 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.[32] Most 18O is produced when 14N (made abundant from CNO burning) captures a 4He nucleus, making 18O common in the helium-rich zones of evolved, massive stars.[32]

Fourteen radioisotopes have been characterized, the most stable being 15O with a half-life of 122.24 seconds (s) and 14O with a half-life of 70.606 s.[31] All of the remaining radioactive isotopes have half-lives that are less than 27 s and the majority of these have half-lives that are less than 83 milliseconds.[31] The most common decay mode of the isotopes lighter than 16O is β+ decay[33][34][35] to yield nitrogen, and the most common mode for the isotopes heavier than 18O is beta decay to yield fluorine.[31]

natural supplements
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