Difference between revisions of "Isotopes of carbon"
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| − | [[Carbon]] has two stable, naturally occurring [[isotope]]s, [[carbon-12]] and [[carbon-13]]. | + | [[Carbon]] has two stable, naturally occurring [[isotope]]s, [[carbon-12]] and [[carbon-13]]. There is also a naturally-occuring radioactive isotope, [[carbon-14]] (''t''<sub>½</sub> = 5700 years), that is formed by the action of [[cosmic ray]]s on the [[Terrestrial atmosphere|Earth's atmosphere]]. [[Carbon-11]] is an artificial isotope used in [[positron emission tomography]] (PET), a medical imaging technique. |
==Atomic weight== | ==Atomic weight== | ||
| Line 14: | Line 14: | ||
| 12 | | 12 | ||
| 0.9893(8) | | 0.9893(8) | ||
| − | | | + | | 0.9885–0.9902 |
|- | |- | ||
| <sup>13</sup>C | | <sup>13</sup>C | ||
| 13.003 354 837 78(98) | | 13.003 354 837 78(98) | ||
| 0.0107(8) | | 0.0107(8) | ||
| − | | | + | | 0.0115–0.0098 |
| + | |- | ||
| + | | colspan=4 | References:<ref name="AME"/> | ||
|- | |- | ||
|} | |} | ||
| − | The standard [[atomic weight]] of carbon has been fixed at its current value since 1995. The range of natural [[isotopic composition]]s 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<sup> | + | The standard [[atomic weight]] of carbon has been fixed at its current value since 1995. The range of natural [[isotopic composition]]s 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<sup>−12</sup>) 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 [[Photosynthesis|photosynthetic reactions]]. The effect is strongest in [[C4-Pathway|C<sub>4</sub>-plants]], predominant in tropical and subtropical climates, and measurements of carbon isotopic compositions are important in [[geochemistry]], [[paleoclimatology]] and [[paleoceanography]]. | + | Carbon-13 is systematically depleted in samples of biological origin (compared to atmospheric [[carbon dioxide]] and most [[Carbonate mineral|carbonate rocks]]) due to a [[kinetic isotope effect]] that is particularly pronounced in [[Photosynthesis|photosynthetic reactions]]. The effect is strongest in [[C4-Pathway|C<sub>4</sub>-plants]], which are predominant in tropical and subtropical climates, and measurements of carbon isotopic compositions are important in [[geochemistry]], [[paleoclimatology]] and [[paleoceanography]]. |
==Radiologically significant isotopes== | ==Radiologically significant isotopes== | ||
Revision as of 10:56, 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.
Atomic weight
| Isotope | Mass/u | Amount fraction |
Normal range |
|---|---|---|---|
| 12C | 12 | 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. 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.
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) | [2][3] |
| 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) | [4][5] |
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, | |||||||||
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.
- ↑ 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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