Difference between revisions of "Isotopes of carbon"
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| <sup>12</sup>C | | <sup>12</sup>C | ||
| − | | 12 | + | | 12 (by definition)<ref group="note" name="C-12">The [[relative atomic mass]] of [[carbon-12]] is exactly twelve [[atomic mass unit]]s, without any [[measurement uncertainty]], by the definition of the atomic mass unit.</ref> |
| 0.9893(8) | | 0.9893(8) | ||
| 0.9885–0.9902 | | 0.9885–0.9902 | ||
Revision as of 11:43, 13 March 2010
Carbon has two stable, naturally occurring isotopes, carbon-12 and carbon-13. There is also a naturally-occuring radioactive isotope, carbon-14 (t½ = 5700 years), that is formed by the action of cosmic rays on the Earth's atmosphere. Carbon-11 is an artificial isotope used in positron emission tomography (PET), a medical imaging technique.
Contents
Atomic weight
| Isotope | Mass/u | Amount fraction |
Normal range |
|---|---|---|---|
| 12C | 12 (by definition)[note 1] | 0.9893(8) | 0.9885–0.9902 |
| 13C | 13.003 354 837 78(98) | 0.0107(8) | 0.0115–0.0098 |
| References:[1] | |||
The standard atomic weight of carbon has been fixed at its current value since 1995. The range of natural isotopic compositions makes a more precise standard value unobtainable, and some terrestrial geological specimens may show compositions outside of the normal range. Natural amounts of carbon-14 (x < 10−12) are insignificant in the calculation of atomic weight.
Carbon-13 is systematically depleted in samples of biological origin (compared to atmospheric carbon dioxide and most carbonate rocks) due to a kinetic isotope effect that is particularly pronounced in photosynthetic reactions.[note 2] The effect is strongest in C4-plants, which are predominant in tropical and subtropical climates, and measurements of carbon isotopic compositions are important in geochemistry, paleoclimatology and paleoceanography. Such measurements have also attracted interest for detecting cases of "doping" in sport:[2] steroid hormones produced by biotechnological methods would be expected to have higher amount fractions of 13C than those produced by an athlete's body.[note 3]
Radiologically significant isotopes
| Isotope | Half life | Decay mode | Energy MeV |
Weighted mean energies/MeV |
Daughter nuclide |
Ref. |
|---|---|---|---|---|---|---|
| 11C | 1223.1(12) s (20.39(2) min) |
β+ (99.759(15)%) | 0.3856(4) | γ, X: 1.02 β, Auger: 0.385 |
115B (stable) | [3][4] |
| γ± (2×99.759%) | 0.5110 | |||||
| X (ec) (0.0002%) | 1.0 × 10−4 | |||||
| K-Auger (0.241(15)%) | 1.7 × 10−4 | |||||
| 14C | 5.70(3) × 103 a | β− (100%) | 0.04947 | β: 0.04947 | 147N (stable) | [5][6] |
All isotopes
| Symbol | Z(p) | N(n) | Mass/u | Excess energy MeV |
Binding energy/A MeV |
β−-decay energy MeV |
Spin | Half life | Decay mode, energy |
|---|---|---|---|---|---|---|---|---|---|
| Excitation energy/MeV | |||||||||
| 8C | 6 | 2 | 8.037 675(25) | 35.094(23) | 3.0978(29) | — | 0 | 2.0(4) zs | 2p (100%) |
| 9C | 6 | 3 | 9.031 0367(23) | 28.9105(21) | 4.337 48(24) | — | (−3⁄2) | 126.5(9) ms | β+ (100%) |
| 10C | 6 | 4 | 10.016 853 23(43) | 15.698 68(40) | 6.032 041(40) | −23.10(40) | 0 | 19.290(12) s | β+ (100%) |
| 11C | 6 | 5 | 11.011 433 61(102) | 10.650 34(95) | 6.676 370(86) | −13.653(46) | −3⁄2 | 20.39(2) min | β+ (100%) |
| 12C | 6 | 6 | 12 | 0 | 7.680 144 | −17.338 08(100) | 0 | STABLE | |
| 13C | 6 | 7 | 13.003 354 837 78(98) | 3.125 011 29(91) | 7.469 849 | −2.220 47(27) | −1⁄2 | STABLE | |
| 14C | 6 | 8 | 14.003 241 9887(41) | 3.019 8931(38) | 7.520 319 | 0.156 476(4) | 0 | 5.70(3) × 103 a | β− (100%) |
| 15C | 6 | 9 | 15.010 5992(86) | 9.873 14(80) | 7.100 169(53) | 9.771 71(80) | +1⁄2 | 2.449(5) s | β− (100%) |
| 16C | 6 | 10 | 16.014 7013(38) | 13.6941(36) | 6.922 05(22) | 8.0105(44) | 0 | 747(8) ms | β− (100%) |
| 17C | 6 | 11 | 17.022 5861(187) | 21.0388(174) | 6.557 62(102) | 13.167(23) | (+3⁄2) | 193(5) ms | β− (100%) |
| 18C | 6 | 12 | 18.026 759(32) | 24.926(30) | 6.425 75(167) | 11.812(35) | 0 | 92(2) ms | β− (100%) |
| 19C | 6 | 13 | 19.034 805(106) | 32.421(98) | 6.1179(52) | 16.559(99) | (+1⁄2) | 46.2(23) ms | β− (100%) |
| 20C | 6 | 14 | 20.040 32(26) | 37.56(24) | 5.9587(120) | 15.79(25) | 0 | 16(3) ms | β− (100%) |
| 21C | 6 | 15 | 21.049 34(54)# | 45.96(50)# | 5.659(24)# | 20.71(51)# | +1⁄2# | <30 ns | ?n |
| 22C | 6 | 16 | 22.057 20(97)# | 53.28(90)# | 5.436(41)# | 21.24(92)# | 0 | 6.2(13) ms | β− (100%) |
| Values marked # are estimated from systematic trends rather than experimentally measured. Spins quoted in parentheses are uncertain in value and/or parity. Sources: Except as otherwise noted, | |||||||||
Notes and references
Notes
- ↑ The relative atomic mass of carbon-12 is exactly twelve atomic mass units, without any measurement uncertainty, by the definition of the atomic mass unit.
- ↑ Marine organisms that obtain carbonate from sea water to construct exoskeletons do not show the depletion of 13C in the exoskeletons: indeed, when such exoskeletons become carbonate rocks, they often show anomalously high amount fractions of 13C, an indication that the carbon did not pass through a photosynthetic pathway.
- ↑ It was shown by Aguilera, Hatton & Catlin (2002) that this was the case in their 2002 samples: however, it is possible to "artificially deplete" the 13C levels in artificial steroid hormones.
References
- ↑ 1.0 1.1 Wapstra, A. H.; Audi, G.; Thibault, C. The AME2003 atomic mass evaluation (I). Evaluation of input data, adjustment procedures. Nucl. Phys. A 2003, 729, 129–336. DOI: 10.1016/j.nuclphysa.2003.11.002. Wapstra, A. H.; Audi, G.; Thibault, C. The AME2003 atomic mass evaluation (II). Tables, graphs, and references. Nucl. Phys. A 2003, 729, 337–676. DOI: 10.1016/j.nuclphysa.2003.11.003. Data tables.
- ↑ Aguilera, Rodrigo; Hatton, Caroline K.; Catlin, Don H. Detection of Epitestosterone Doping by Isotope Ratio Mass Spectrometry. Clin. Chem. 2002, 48, 629–36.
- ↑ ENSDF Decay Data in the MIRD (Medical Internal Radiation Dose) Format for 11C; National Nuclear Data Center, <http://www.nndc.bnl.gov/useroutput/11c_mird.html>. (accessed 13 March 2010).
- ↑ Ajzenberg-Selove, F. Energy levels of light nuclei A = 11–12. Nucl. Phys. A 1990, 506 (1), 1–158. DOI: 10.1016/0375-9474(90)90271-M.
- ↑ ENSDF Decay Data in the MIRD (Medical Internal Radiation Dose) Format for 14C; National Nuclear Data Center, <http://www.nndc.bnl.gov/useroutput/14c_mird.html>. (accessed 13 March 2010).
- ↑ Ajzenberg-Selove, F. Energy levels of light nuclei A = 13–15. Nucl. Phys. A 1991, 523 (1), 1–196. DOI: 10.1016/0375-9474(91)90446-D.
- ↑ Audi, G.; Bersillon, O.; Blachot, J.; Wapstra, A. H. The NUBASE evaluation of nuclear and decay properties. Nucl. Phys. A 2003, 729, 3–128. doi:10.1016/j.nuclphysa.2003.11.001, <http://amdc.in2p3.fr/nubase/Nubase2003.pdf>.
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