Isotopes of oxygen

There are three known stable isotopes of oxygen (₈O): ¹⁶
O, ¹⁷
O, and ¹⁸
O. Radioisotopes are known from ¹¹O to ²⁸O (particle-bound from mass number 13 to 24), and the most stable are ¹⁵
O with half-life 122.27 seconds and ¹⁴
O with half-life 70.62 seconds. All remaining radioisotopes are even shorter in lifetime. The four heaviest known isotopes (up to ²⁸
O) decay by neutron emission to ²⁴
O, whose half-life is 77 milliseconds; ²⁴O, along with ²⁸Ne, have been used in the model of reactions in the crust of neutron stars.^[4] The most common decay mode for isotopes lighter than the stable isotopes is β⁺ decay to nitrogen, and the most common mode after is β⁻ decay to fluorine.

Isotopes of oxygen (₈O)

Main isotopes[1] Decay Isotope abun­dance half-life (t1/2) mode pro­duct 15O trace 122.27 s β+ 15N 16O 99.8% stable 17O 0.0384% stable 18O 0.205% stable
Standard atomic weight Ar°(O)
	[15.99903, 15.99977][2] 15.999±0.001 (abridged)[3]

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[5] [n 2]	Half-life[1] [resonance width]	Decay mode[1] [n 3]	Daughter isotope [n 4]	Spin and parity[1] [n 5][n 6]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion[1]	Range of variation
11 O[6]	8	3	11.05125(6)	198(12) ys [2.31(14) MeV]	2p	9 C	(3/2−)
12 O	8	4	12.034368(13)	8.9(3.3) zs	2p	10 C	0+
13 O	8	5	13.024815(10)	8.58(5) ms	β+ (89.1(2)%)	13 N	(3/2−)
					β+p (10.9(2)%)	12 C
					β+p,α (<0.1%)	24 He[7]
14 O	8	6	14.008596706(27)	70.621(11) s	β+	14 N	0+
15 O[n 7]	8	7	15.0030656(5)	122.266(43) s	β+	15 N	1/2−	Trace[8]
16 O[n 8]	8	8	15.994914619257(319)	Stable			0+	[0.99738, 0.99776][9]
17 O[n 9]	8	9	16.999131755953(692)	Stable			5/2+	[0.000367, 0.000400][9]
18 O[n 8][n 10]	8	10	17.999159612136(690)	Stable			0+	[0.00187, 0.00222][9]
19 O	8	11	19.0035780(28)	26.470(6) s	β−	19 F	5/2+
20 O	8	12	20.0040754(9)	13.51(5) s	β−	20 F	0+
21 O	8	13	21.008655(13)	3.42(10) s	β−	21 F	(5/2+)
					β−n ?	20 F ?
22 O	8	14	22.00997(6)	2.25(9) s	β− (> 78%)	22 F	0+
					β−n (< 22%)	21 F
23 O	8	15	23.01570(13)	97(8) ms	β− (93(2)%)	23 F	1/2+
					β−n (7(2)%)	22 F
24 O[n 11]	8	16	24.01986(18)	77.4(4.5) ms	β− (57(4)%)	24 F	0+
					β−n (43(4)%)	23 F
25 O	8	17	25.02934(18)	5.18(35) zs	n	24 O	3/2+#
26 O	8	18	26.03721(18)	4.2(3.3) ps	2n	24 O	0+
27 O[10]	8	19		≥ 2.5 zs	n	26 O	(3/2+, 7/2−)
28 O[10]	8	20		≥ 650 ys	2n	26 O	0+
This table header & footer:

1. ^mO – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. Modes of decay:

   n:	Neutron emission
   p:	Proton emission

4. Bold symbol as daughter – Daughter product is stable.
5. ( ) spin value – Indicates spin with weak assignment arguments.
6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
7. Intermediate product of CNO-I in stellar nucleosynthesis as part of the process producing helium from hydrogen
8. The ratio between ¹⁶
   O and ¹⁸
   O is used to deduce ancient temperatures.
9. Can be used in NMR studies of metabolic pathways.
10. Can be used in studying certain metabolic pathways.
11. Heaviest particle-bound isotope of oxygen, see Nuclear drip line

Stable isotopes

 

Late in a massive star's life, ¹⁶
O concentrates in the Ne-shell, ¹⁷
O in the H-shell and ¹⁸
O in the He-shell.

Natural oxygen is made of three stable isotopes, ¹⁶
O, ¹⁷
O, and ¹⁸
O, with ¹⁶
O being the most abundant (about 99.76%). Depending on the terrestrial source, the standard atomic weight varies within the range of [15.99903, 15.99977] (the conventional value is 15.999).

¹⁶
O has high relative and absolute abundance because it is a principal product of stellar evolution and because it is a primary isotope, meaning it can be made by stars that were initially hydrogen only.^[11] Most ¹⁶
O is synthesized at the end of the helium fusion process in stars; the triple-alpha process creates ¹²
C, which captures an additional ⁴
He nucleus to produce ¹⁶
O. The neon burning process creates additional ¹⁶
O.^[11]

Both ¹⁷
O and ¹⁸
O are secondary isotopes, meaning their synthesis requires seed nuclei. ¹⁷
O is primarily made by burning hydrogen into helium in the CNO cycle, making it a common isotope in the hydrogen burning zones of stars.^[11] Most ¹⁸
O is produced when ¹⁴
N (made abundant from CNO burning) captures a ⁴
He nucleus, becoming ¹⁸
F. This quickly (half-life around 110 minutes) beta decays to ¹⁸
O making that isotope common in the helium-rich zones of stars.^[11] Temperatures on the order of 10⁹ kelvins are needed to fuse oxygen into sulfur.^[12]

An atomic mass of 16 was assigned to oxygen prior to the definition of the dalton based on ¹²
C.^[13] Since physicists referred to ¹⁶
O only, while chemists meant the natural mix of isotopes, this led to slightly different mass scales.

Applications

Measurements of ¹⁸O/¹⁶O ratio are often used to interpret changes in paleoclimate. Oxygen in Earth's air is 99.757% ¹⁶
O, 0.039% ¹⁷
O and 0.204% ¹⁸
O.^[14] Water molecules with a lighter isotope are slightly more likely to evaporate and less likely to fall as precipitation,^[15] so Earth's freshwater and polar ice have slightly less (0.1981%) ¹⁸
O than air (0.204%) or seawater (0.1995%). This disparity allows analysis of temperature patterns via historic ice cores.

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

Due to natural oxygen being mostly ¹⁶
O, samples enriched with the other stable isotopes can be used for isotope labeling. For example, it was proven that the oxygen released in photosynthesis originates in H₂O, rather than in the also consumed CO₂, by isotope tracing experiments. The oxygen contained in CO₂ in turn is used to make up the sugars formed by photosynthesis.

In heavy-water nuclear reactors the neutron moderator should preferably be low in ¹⁷
O and ¹⁸
O due to their higher neutron absorption cross section compared to ¹⁶
O. While this effect can also be observed in light-water reactors, ordinary hydrogen (protium) has a higher absorption cross section than any stable isotope of oxygen and its number density is twice as high in water as that of oxygen, so that the effect is negligible. As some methods of isotope separation enrich not only heavier isotopes of hydrogen but also heavier isotopes of oxygen when producing heavy water, the concentration of ¹⁷
O and ¹⁸
O can be measurably higher. Furthermore, the ¹⁷
O(n,α)¹⁴
C reaction is a further undesirable result of an elevated concentration of heavier isotopes of oxygen. Therefore, facilities which remove tritium from heavy water used in nuclear reactors often also remove or at least reduce the amount of heavier isotopes of oxygen.

Oxygen isotopes are also used to trace ocean composition and temperature which seafood is from.^[17]

Oxygen-14

Oxygen-14 (half-life 70.62 seconds) is the second most stable radioisotope of oxygen, and decays by positron emission to nitrogen-14.

Oxygen-14 ion beams are of interest to researchers of proton-rich nuclei; for example, one early experiment at the Facility for Rare Isotope Beams in East Lansing, Michigan, produced a ¹⁴O beam by proton bombardment of ¹⁴N,^[18][19] using it to determine the absolute strength of the electron capture transition.

Oxygen-15

Oxygen-15 (half-life 122.27 seconds) is the most stable radioisotope of oxygen, decaying by positron emission to nitrogen-15.

It is thus the isotope of oxygen used in positron emission tomography (PET). It can be used in, among other things, water for PET myocardial perfusion imaging and for brain imaging.^[20][21] It is produced for this application through deuteron bombardment of nitrogen-14 using a cyclotron.^[22]

¹⁴
N + ²
H → ¹⁵
O + n

Oxygen-15 and nitrogen-13 are produced in air when gamma rays (for example from lightning) knock neutrons^[23] out of ¹⁶O and ¹⁴N:^[24]

¹⁶
O + γ → ¹⁵
O + n

¹⁴
N + γ → ¹³
N + n

¹⁵
O decays to ¹⁵
N, emitting a positron. The positron quickly annihilates with an electron, producing two gamma rays of about 511 keV. After a lightning bolt, this gamma radiation dies down with half-life of 2 minutes, but these low-energy gamma rays go on average only about 90 metres through the air. Together with rays produced from positrons from nitrogen-13 they may only be detected for a minute or so as the "cloud" of ¹⁵
O and ¹³
N floats by, carried by the wind.^[8]

See also

• Dole effect

Daughter products other than oxygen

• Isotopes of fluorine
• Isotopes of nitrogen
• Isotopes of carbon
• Isotopes of helium

References

1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
2. "Standard Atomic Weights: Oxygen". CIAAW. 2009.
3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
4. Berry, D.K; Horowitz, C.J (April 2008). "Fusion of neutron rich oxygen isotopes in the crust of accreting neutron stars". Physical Review C. 77 (4): 045807. arXiv:0710.5714. Bibcode:2008PhRvC..77d5807H. doi:10.1103/PhysRevC.77.045807. S2CID 118639621.
5. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
6. Webb, T. B.; et al. (2019). "First Observation of Unbound ¹¹O, the Mirror of the Halo Nucleus ¹¹Li". Physical Review Letters. 122 (12): 122501–1–122501–7. arXiv:1812.08880. Bibcode:2019PhRvL.122l2501W. doi:10.1103/PhysRevLett.122.122501. PMID 30978039. S2CID 84841752.
7. Paleja, Ameya (2023-09-05). "Scientists observe nucleus decay into four particles". interestingengineering.com. Retrieved 2023-09-29.
8. Teruaki Enoto; et al. (Nov 23, 2017). "Photonuclear reactions triggered by lightning discharge". Nature. 551 (7681): 481–484. arXiv:1711.08044. Bibcode:2017Natur.551..481E. doi:10.1038/nature24630. PMID 29168803. S2CID 4388159.
9. "Atomic Weight of Oxygen | Commission on Isotopic Abundances and Atomic Weights". ciaaw.org. Retrieved 2022-03-15.
10. Kondo, Y.; Achouri, N. L.; Falou, H. Al; et al. (2023-08-30). "First observation of 28O". Nature. 620 (7976). Springer Science and Business Media LLC: 965–970. Bibcode:2023Natur.620..965K. doi:10.1038/s41586-023-06352-6. ISSN 0028-0836. PMC 10630140. PMID 37648757.
11. B. S. Meyer (September 19–21, 2005). "Nucleosynthesis and galactic chemical evolution of the isotopes of oxygen" (PDF). Proceedings of the NASA Cosmochemistry Program and the Lunar and Planetary Institute. Workgroup on Oxygen in the Earliest Solar System. Gatlinburg, Tennessee. 9022.
12. Emsley 2001, p. 297. sfn error: no target: CITEREFEmsley2001 (help)
13. Parks & Mellor 1939, Chapter VI, Section 7. sfn error: no target: CITEREFParksMellor1939 (help)
14. Cook & Lauer 1968, p. 500. sfn error: no target: CITEREFCookLauer1968 (help)
15. Dansgaard, W (1964). "Stable isotopes in precipitation" (PDF). Tellus. 16 (4): 436–468. Bibcode:1964Tell...16..436D. doi:10.1111/j.2153-3490.1964.tb00181.x.
16. 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.
17. Martino, Jasmin C.; Trueman, Clive N.; Mazumder, Debashish; Crawford, Jagoda; Doubleday, Zoë A. (September 12, 2022). "Using 'chemical fingerprinting' to fight seafood fraud and illegal fishing". Fish and Fisheries. 23 (6). Phys.org: 1455–1468. doi:10.1111/faf.12703. S2CID 252173914. Archived from the original on September 13, 2022. Retrieved September 13, 2022.
18. "APS -Fall 2022 Meeting of the APS Division of Nuclear Physics - Event - Oxygen-14 Beam Production at 5 and 15 MeV/u with MARS Spectrometer". Bulletin of the American Physical Society. 67 (17). American Physical Society.
19. Energy, US Department of. "Researchers develop a novel method to study nuclear reactions on short-lived isotopes involved in explosions of stars". phys.org. Retrieved 16 December 2023.
20. Rischpler, Christoph; Higuchi, Takahiro; Nekolla, Stephan G. (22 November 2014). "Current and Future Status of PET Myocardial Perfusion Tracers". Current Cardiovascular Imaging Reports. 8 (1): 333–343. doi:10.1007/s12410-014-9303-z. S2CID 72703962.
21. Kim, E. Edmund; Lee, Myung-Chul; Inoue, Tomio; Wong, Wai-Hoi (2012). Clinical PET and PET/CT: Principles and Applications. Springer. p. 182. ISBN 9781441908025.
22. "Production of PET Radionuclides". Austin Hospital, Austin Health. Archived from the original on 15 January 2013. Retrieved 6 December 2012.
23. If protons were knocked out, the stable isotopes ¹³C and ¹⁵N would be formed.
24. Timmer, John (25 November 2017). "Lightning strikes leave behind a radioactive cloud". Ars Technica.