Isotopes of carbon

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Carbon has two stable, naturally occurring isotopes, carbon-12 and carbon-13.

Atomic weight

Ar(6C) = 12.0107(8)
Isotope Mass/u Amount
fraction
Normal
range
12C 12 0.9893(8)
13C 13.003 354 837 78(98) 0.0107(8)

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, 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) [1][2]
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) [3][4]

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) (−32) 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) 32 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) 12 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) +12 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) (+32) 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) (+12) 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)# +12# <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,
isotopic masses and associated energies are taken from the AME 2003 dataset;[5]
nuclear spins and decay properties are taken from NUBASE 2003.[6]

References

  1. 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).
  2. 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.
  3. 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).
  4. 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.
  5. 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.
  6. 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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