Oxygen-16 (16O) is a stable isotope of oxygen, having 8 neutrons and 8 protons in its nucleus. It has a mass of 15.99491461956 u. Oxygen-16 is the most abundant isotope of oxygen and accounts for 99.762% of oxygen's natural abundance.[2] The relative and absolute abundance of 16O are high because it is a principal product of stellar evolution and because it is a primordial isotope, meaning it can be made by stars that were initially made exclusively of hydrogen. Most 16O is synthesized at the end of the helium fusion process in stars; the triple-alpha process creates 12C, which captures an additional 4He to make 16O. The neon-burning process creates additional 16O. Oxygen-16 is doubly magic.

Oxygen-16, 16O
Namesoxygen-16, 16O, O-16
Protons (Z)8
Neutrons (N)8
Nuclide data
Natural abundance99.76%
Half-life (t1/2)stable
Isotope mass15.99491461956 Da
Excess energy−4737.00135(16)[1] keV
Isotopes of oxygen
Complete table of nuclides

Solid samples (organic and inorganic) for 16O studies are usually stored in silver cups and measured with pyrolysis and mass spectrometry.[3] Researchers need to avoid improper or prolonged storage of the samples for accurate measurements.[3]

Oxygen-16 was originally the standard from which the atomic masses of all nuclides were defined, i.e., one atomic mass unit was defined as 116 the mass of oxygen-16, though the atomic mass unit has since been redefined relative to carbon-12.


  1. ^ Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF). Chinese Physics C. 41 (3): 030003–8. doi:10.1088/1674-1137/41/3/030003.
  2. ^ "Table of Isotopic Masses and Natural Abundances" (PDF). 1999.
  3. ^ a b Tsang, Man-Yin; Yao, Weiqi; Tse, Kevin (2020). Kim, Il-Nam (ed.). "Oxidized silver cups can skew oxygen isotope results of small samples". Experimental Results. 1: e12. doi:10.1017/exp.2020.15. ISSN 2516-712X.