Isotopes of carbon

List of isotopes

Carbon-21 |-id=Carbon-8 | | | [] | 2p | Also immediately emits two protons for the net reaction of → **** + **4 ** | 0+ | | |-id=Carbon-9 | β+ ()

| |- | β+p () | |-id=Carbon-10 | | | | β+ | **** | 0+ | | |- | β+ | **** |-id=Carbon-11m | | p? | **** ? | 1/2+ | | |-id=Carbon-12 | | 12 exactlyThe dalton is defined as 1/12 of the mass of an unbound atom of carbon-12 in its ground state. | 0+ | [, ] |-id=Carbon-13 | Ratio of 12C to 13C used to measure biological productivity in ancient times and differing types of photosynthesis | | 1/2− | [, ] |-id=Carbon-14 | Has an important use in radiodating (see carbon dating) | | | β− | **** | 0+ | TracePrimarily cosmogenic, produced by neutrons striking atoms of ( + → + ) | −12 |-id=Carbon-14m | | IT | | (2−) | | |-id=Carbon-15 | | | | β− | **** | 1/2+ | | |-id=Carbon-16 | β−n ()

| |-id=Carbon-17 | β− () | |- | β−n () | |- | β−2n ? | **** ? |-id=Carbon-18 | β− () | |- | β−n () | |- | β−2n ? | ? |-id=Carbon-19 | β−n () | |- | β− () | |- | β−2n () | |-id=Carbon-20 | β−n () | |- | β−2n ( | |- | β− ( ) | | ?This isotope has not yet been observed; given data is inferred or estimated from periodic trends. | # | | n ? | ? | 1/2+# | |-- |-id=Carbon-22 | β−n () | |- | β−2n ( | |- | β− ( ) | | ? | # | | n ? | ? | 3/2+# | |

Carbon-11

Carbon-11 or **** is a radioactive isotope of carbon that decays to boron-11 with a half-life to 20.34 minutes. This decay mainly occurs due to positron emission, with around 0.19–0.23% of decays instead occurring by electron capture. : → + + + : + → + +

It is produced by hitting nitrogen with protons of around 16.5 MeV in a cyclotron. The causes the endothermic reaction : + → + − 2.92 MeV

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

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 []DASB and []Cimbi-5.

Stable isotopes

Main article: Carbon-12, Carbon-13

Carbon-12 and carbon-13 account for approximately 98.9% and 1.1% (respectively) of the naturally occurring carbon on Earth. However, the ratio of stable 13C and 12C in a material can vary due to differences in precursor source and isotopic fractionation induced by a variety of biogeochemical processes. The quantities of the different isotopes are commonly measured via isotope ratio mass spectrometry and expressed as parts per thousand (‰ or "per mille") divergence from the ratio of a standard: : \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 ‰

Peedee Belemnite ("PDB"), a fossil belemnite, was the original reference standard used for standardizing isotope ratio values. Due to the depletion of the original PDB, artificial "Vienna PDB", or "VPDB", is generally used today.

Paleoclimate

and 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). Plants find it easier to use the lighter isotope () when they convert sunlight and carbon dioxide into food. For example, large blooms of plankton (free-floating organisms) absorb large amounts of from the oceans. Originally, the 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 from the surface, leaving the surface layers relatively rich in . Where cold waters well up from the depths (such as in the North Atlantic), the water carries back up with it; when the ocean was less stratified than today, there was much more in the skeletons of surface-dwelling species. Other indicators of past climate include the presence of tropical species and coral growth rings.

Tracing food sources and diets

Different photosynthetic pathways preferentially select for the lighter , but their selectivity differs. 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‰.

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.

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

In 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).

Carbon-14

Main article: Carbon-14

Carbon-14 (also called radiocarbon) occurs in trace amounts and has a half-life of 5700 years. The primary source of on Earth is the reaction of with thermal neutrons from cosmic radiation in the upper atmosphere; this mixes throughout the atmosphere, and biological processes such as photosynthesis incorporate the into living organisms. Since organisms stop absorbing upon dying, measurement of the amount of in a sample may be used to estimate its age. This technique is called radiocarbon dating and is one of the principal methods of radiometric dating in the field of archaeology.

References

References

1. "Atomic Weight of Carbon".
2. (1 September 1957). "K-capture in carbon 11". Philosophical Magazine.
3. (1967-04-11). "The ratio of K-capture to positron emission in the decay of ¹¹C". Nuclear Physics A.
4. "Carbon-11 Production and Transformation".
5. (Jan 18, 2024). "Gas Phase Transformations in Carbon-11 Chemistry". Int. J. Mol. Sci..
6. Daria Boscolo. (2025). "Image-guided treatment of mouse tumours with radioactive ion beams". Nature Physics.
7. (2012). "Biological oceanography". John Wiley & Sons, Ltd..
8. (1995). "The influence of air-sea exchange on the isotopic composition of oceanic carbon: Observations and modeling". Global Biogeochemical Cycles.
9. [[Tim Flannery]] ''The weather makers: the history & future of climate change'', The Text Publishing Company, Melbourne, Australia. {{ISBN. 1-920885-84-6
10. (May 1988). "Carbon Isotopes in Photosynthesis". BioScience.
11. Tycot, R. H.. (2004). "Stable isotopes and diet: you are what you eat". Proceedings of the International School of Physics "Enrico Fermi" Course CLIV.
12. (2006). "Where does our protein come from?". British Journal of Nutrition.