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Isotopes of carbon
Type of stable carbon atoms

Carbon (6C) has 14 known isotopes, from 8C to 20C as well as 22C, of which only 12C and 13C are stable. The longest-lived radioisotope is 14C, with a half-life of 5.70(3)×103 years. This is also the only carbon radioisotope found in nature, as trace quantities are formed cosmogenically by the reaction 14N + n → 14C + 1H. The most stable artificial radioisotope is 11C, which has a half-life of 20.3402(53) min. All other radioisotopes have half-lives under 20 seconds, most less than 200 milliseconds. The least stable isotope is 8C, with a half-life of 3.5(1.4)×10−21 s. Light isotopes tend to decay into isotopes of boron and heavy ones tend to decay into isotopes of nitrogen.

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List of isotopes

NuclideZNIsotopic mass (Da)12Half-life3[resonance width]Decaymode45Daughterisotope6Spin andparity789Natural abundance (mole fraction)
Normal proportion10Range of variation
8C628.037643(20)3.5(1.4) zs[230(50) keV]2p6Be110+
9C639.0310372(23)126.5(9) msβ+ (54.1(1.7)%)9B3/2−
β+α (38.4(1.6)%)5Li12
β+p (7.5(6)%)8Be13
10C6410.01685322(8)19.3011(15) sβ+10B0+
11C146511.01143260(6)20.3402(53) minβ+11B3/2−
11mC12160(40) keVp ?1510B ?1/2+
12C6612 exactly16Stable0+[0.9884, 0.9904]17
13C186713.003354835336(252)Stable1/2−[0.0096, 0.0116]19
14C206814.003241989(4)5.70(3)×103 yβ−14N0+Trace21< 10−12
14mC22100(100) keVIT14C(2−)
15C6915.0105993(9)2.449(5) sβ−15N1/2+
16C61016.014701(4)750(6) msβ−n (99.0(3)%)15N0+
β− (1.0(3)%)16N
17C61117.022579(19)193(6) msβ− (71.6(1.3)%)17N3/2+
β−n (28.4(1.3)%)16N
β−2n ?2215N ?
18C61218.02675(3)92(2) msβ− (68.5(1.5)%)18N0+
β−n (31.5(1.5)%)17N
β−2n ?2316N ?
19C2461319.03480(11)46.2(2.3) msβ−n (47(3)%)18N1/2+
β− (46.0(4.2)%)19N
β−2n (7(3)%)17N
20C61420.04026(25)16(3) msβ−n (70(11)%)19N0+
β−2n (< 18.6%)18N
β− (> 11.4%)20N
22C2561622.05755(25)6.2(1.3) msβ−n (61(14)%)21N0+
β−2n (< 37%)20N
β− (> 2%)22N
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Carbon-11

Carbon-11 or 11C is a radioactive isotope of carbon that decays to boron-11. This decay mainly occurs due to positron emission, with around 0.19–0.23% of decays instead occurring by electron capture.2627 It has a half-life of 20.3402(53) min.

11C → 11B + e+ + νe + 0.96 MeV 11C + e− → 11B + νe + 1.98 MeV

It is produced by hitting nitrogen with protons of around 16.5 MeV in a cyclotron. The causes the endothermic reaction2829

14N + p → 11C + 4He − 2.92 MeV

It can also be produced by fragmentation of 12C by shooting high-energy 12C at a target.30

Carbon-11 is commonly used as a radioisotope for the radioactive labeling of molecules in positron emission tomography. Among the many molecules used in this context are the radioligands [11C]DASB and [11C]Cimbi-5.

Natural isotopes

Main articles: Carbon-12, Carbon-13, and Carbon-14

There are three naturally occurring isotopes of carbon: 12, 13, and 14. 12C and 13C are stable, occurring in a natural proportion of approximately 93:1. 14C is produced by thermal neutrons from cosmic radiation in the upper atmosphere, and is transported down to earth to be absorbed by living biological material. Isotopically, 14C constitutes a negligible part; but, since it is radioactive with a half-life of 5.70(3)×103 years, it is radiometrically detectable. Since dead tissue does not absorb 14C, the amount of 14C is one of the methods used within the field of archeology for radiometric dating of biological material.

Paleoclimate

12C and 13C are measured as the isotope ratio δ13C in benthic foraminifera and used as a proxy for nutrient cycling and the temperature dependent air–sea exchange of CO2 (ventilation).31 Plants find it easier to use the lighter isotopes (12C) when they convert sunlight and carbon dioxide into food. For example, large blooms of plankton (free-floating organisms) absorb large amounts of 12C from the oceans. Originally, the 12C was mostly incorporated into the seawater from the atmosphere. If the oceans that the plankton live in are stratified (meaning that there are layers of warm water near the top, and colder water deeper down), then the surface water does not mix very much with the deeper waters, so that when the plankton dies, it sinks and takes away 12C from the surface, leaving the surface layers relatively rich in 13C. Where cold waters well up from the depths (such as in the North Atlantic), the water carries 12C back up with it; when the ocean was less stratified than today, there was much more 12C in the skeletons of surface-dwelling species. Other indicators of past climate include the presence of tropical species and coral growth rings.32

Tracing food sources and diets

The quantities of the different isotopes can be measured by mass spectrometry and compared to a standard; the result (e.g., the delta of the 13C = δ13C) is expressed as parts per thousand (‰) divergence from the ratio of a standard:33

δ <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> C <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> 13 = ( ( <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> C <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> 13 <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> C <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> 12 ) sample ( <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> C <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> 13 <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> C <23x15px|border_|alt=vosges_(department)|link=vosges_(department)_communes_of_the_vosges_department343> 12 ) standard − 1 ) × 1000 {\displaystyle \delta {\ce {^{13}C}}=\left({\frac {\left({\frac {{\ce {^{13}C}}}{{\ce {^{12}C}}}}\right)_{\text{sample}}}{\left({\frac {{\ce {^{13}C}}}{{\ce {^{12}C}}}}\right)_{\text{standard}}}}-1\right)\times 1000} ‰

The usual standard is Peedee Belemnite, abbreviated "PDB", a fossil belemnite. Due to shortage of the original PDB sample, artificial "virtual PDB", or "VPDB", is generally used today.34

Stable carbon isotopes in carbon dioxide are utilized differentially by plants during photosynthesis. Grasses in temperate climates (barley, rice, wheat, rye, and oats, plus sunflower, potato, tomatoes, peanuts, cotton, sugar beet, and most trees and their nuts or fruits, roses, and Kentucky bluegrass) follow a C3 photosynthetic pathway that will yield δ13C values averaging about −26.5‰. Grasses in hot arid climates (maize in particular, but also millet, sorghum, sugar cane, and crabgrass) follow a C4 photosynthetic pathway that produces δ13C values averaging about −12.5‰.35

It follows that eating these different plants will affect the δ13C values in the consumer's body tissues. If an animal (or human) eats only C3 plants, their δ13C values will be from −18.5 to −22.0‰ in their bone collagen and −14.5‰ in the hydroxylapatite of their teeth and bones.36

In contrast, C4 feeders will have bone collagen with a value of −7.5‰ and hydroxylapatite value of −0.5‰.

In actual case studies, millet and maize eaters can easily be distinguished from rice and wheat eaters. Studying how these dietary preferences are distributed geographically through time can illuminate migration paths of people and dispersal paths of different agricultural crops. However, human groups have often mixed C3 and C4 plants (northern Chinese historically subsisted on wheat and millet), or mixed plant and animal groups together (for example, southeastern Chinese subsisting on rice and fish).37

See also

References

  1. 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. /wiki/Doi_(identifier) ↩

  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits. ↩

  3. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

  4. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

  5. Modes of decay: EC:Electron capturen:Neutron emissionp:Proton emission /wiki/Electron_capture ↩

  6. Bold symbol as daughter – Daughter product is stable. ↩

  7. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

  8. ( ) spin value – Indicates spin with weak assignment arguments. ↩

  9. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩

  10. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩

  11. Subsequently decays by double proton emission to 4He for a net reaction of 8C → 4He + 41H ↩

  12. Immediately decays by proton emission to 4He for a net reaction of 9C → 2 4He + 1H + e+ ↩

  13. Immediately decays into two 4He atoms for a net reaction of 9C → 2 4He + 1H + e+ ↩

  14. Used for labeling molecules in PET scans /wiki/Positron_emission_tomography ↩

  15. Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide. ↩

  16. The unified atomic mass unit is defined as 1/12 of the mass of an unbound atom of carbon-12 in its ground state. /wiki/Unified_atomic_mass_unit ↩

  17. "Atomic Weight of Carbon". CIAAW. https://ciaaw.org/carbon.htm ↩

  18. Ratio of 12C to 13C used to measure biological productivity in ancient times and differing types of photosynthesis /wiki/%CE%9413C ↩

  19. "Atomic Weight of Carbon". CIAAW. https://ciaaw.org/carbon.htm ↩

  20. Has an important use in radiodating (see carbon dating) /wiki/Radiodating ↩

  21. Primarily cosmogenic, produced by neutrons striking atoms of 14N (14N + n → 14C + 1H) /wiki/Cosmogenic ↩

  22. Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide. ↩

  23. Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide. ↩

  24. Has 1 halo neutron /wiki/Halo_nucleus ↩

  25. Has 2 halo neutrons ↩

  26. Scobie, J.; Lewis, G. M. (1 September 1957). "K-capture in carbon 11". Philosophical Magazine. 2 (21): 1089–1099. Bibcode:1957PMag....2.1089S. doi:10.1080/14786435708242737. /wiki/Bibcode_(identifier) ↩

  27. Campbell, J. L.; Leiper, W.; Ledingham, K. W. D.; Drever, R. W. P. (1967-04-11). "The ratio of K-capture to positron emission in the decay of 11C". Nuclear Physics A. 96 (2): 279–287. Bibcode:1967NuPhA..96..279C. doi:10.1016/0375-9474(67)90712-9. /wiki/Bibcode_(identifier) ↩

  28. "Carbon-11 Production and Transformation". Scholarly Community Encyclopedia. https://encyclopedia.pub/entry/54549 ↩

  29. Lu, Shuiyu; et al. (Jan 18, 2024). "Gas Phase Transformations in Carbon-11 Chemistry". Int. J. Mol. Sci. 25 (2): 1167. doi:10.3390/ijms25021167. PMC 10816134. PMID 38256240. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10816134 ↩

  30. Daria Boscolo; et al. (Sep 2024). "First image-guided treatment of a mouse tumor with radioactive ion beams". arXiv:2409.14898. https://arxiv.org/abs/2409.14898 ↩

  31. Lynch-Stieglitz, Jean; Stocker, Thomas F.; Broecker, Wallace S.; Fairbanks, Richard G. (1995). "The influence of air-sea exchange on the isotopic composition of oceanic carbon: Observations and modeling". Global Biogeochemical Cycles. 9 (4): 653–665. Bibcode:1995GBioC...9..653L. doi:10.1029/95GB02574. S2CID 129194624. https://boris.unibe.ch/158803/ ↩

  32. Tim Flannery The weather makers: the history & future of climate change, The Text Publishing Company, Melbourne, Australia. ISBN 1-920885-84-6 /wiki/Tim_Flannery ↩

  33. Miller, Charles B.; Wheeler, Patricia (2012). Biological oceanography (2nd ed.). Chichester, West Sussex: John Wiley & Sons, Ltd. p. 186. ISBN 9781444333022. OCLC 794619582. 9781444333022 ↩

  34. Faure, Gunter; Mensing, Teresa M. (2005). "27 Carbon". Isotopes: Principles and Applications (Third ed.). Hoboken, NJ: Wiley. ISBN 978-81-265-3837-9. 978-81-265-3837-9 ↩

  35. O'Leary, Marion H. (May 1988). "Carbon Isotopes in Photosynthesis" (PDF). BioScience. 38 (5): 328–336. doi:10.2307/1310735. JSTOR 1310735. S2CID 29110460. Retrieved 17 November 2022. https://www.ldeo.columbia.edu/~polissar/OrgGeochem/oleary-1988-carbon-isotopes.pdf ↩

  36. Tycot, R. H. (2004). M. Martini; M. Milazzo; M. Piacentini (eds.). "Stable isotopes and diet: you are what you eat" (PDF). Proceedings of the International School of Physics "Enrico Fermi" Course CLIV. http://luna.cas.usf.edu/~rtykot/PR39%20-%20Enrico%20Fermi%20isotopes.pdf ↩

  37. Richard, Hedges (2006). "Where does our protein come from?". British Journal of Nutrition. 95 (6): 1031–2. doi:10.1079/bjn20061782. PMID 16768822. https://doi.org/10.1079%2Fbjn20061782 ↩