Carbon-18

Properties and data of the isotope ¹⁸C.

Contents

Carbon-18 is a radioisotope of the chemical element carbon, which has 12 neutrons in its atomic nucleus in addition to the element-specific 6 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 18. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ¹⁸C is exclusively for academic purposes.

The radioactive isotope was first detected in experiments in which thorium-232 was irradiated with oxygen-18 ions accelerated to 122 MeV; the corresponding report was published in 1969 [1].

See also: List of individual Carbon isotopes (and general data sources).

General data

Name of the isotope:Carbon-18; C-18Symbol:¹⁸C or 186CMass number A:18 (= number of nucleons)Atomic number Z:6 (= number of protons)Neutrons N:12Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):2 (= neutron-proton ratio)Neutron excess (N-Z):6Isotopic mass:18.02675(3) u (atomic weight of Carbon-18)Nuclide mass:18.0234585 u (calculated nuclear mass without electrons)Mass excess:24.91746 MeVMass defect:0.124179184 u (per nucleus)Nuclear binding energy:115.67216482 MeV (per nucleus)
6.42623138 MeV (average binding energy per nucleon)Separation energy:S_N = 4.184(35) MeV (first neutron)
S_P = 26.086(206) MeV (first proton)Half-life:92(2) msDecay constant λ:7.5342084843472 s^-1Specific activity α:2.520670264492 × 10⁺²³ Bq g^-1
6812622336467 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Isobaric spin: 3Quadrupole moment Q:+0.0123(12) barn (100 fm²)Charge radius:2.600 femtometer fmMatter radius:3.065 femtometer fmMirror nucleus:Magnesium-18Year of discovery:1969

Radioactive Decay

Half-life T_½ = 92(2) ms respectively 9.2 × 10^-2 seconds s.

Decay mode	Daughter	Probability	Decay energy
β^-	¹⁸N	68.5 %	11.81(4) MeV
β^-, n	¹⁷N	31.5(5) %	8.978(34) MeV
β^-, 2n	¹⁶N	?

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 12) and isobaric (same nucleon number A = 18) with Carbon-18. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 12	Isobar A = 18
4	¹⁶Be
5	¹⁷B	¹⁸B
6	¹⁸C	¹⁸C
7	¹⁹N	¹⁸N
8	²⁰O	¹⁸O
9	²¹F	¹⁸F
10	²²Ne	¹⁸Ne
11	²³Na	¹⁸Na
12	²⁴Mg	¹⁸Mg
13	²⁵Al
14	²⁶Si
15	²⁷P
16	²⁸S
17	²⁹Cl
18	³⁰Ar
19	³¹K

External data and identifiers

Adopted Levels, Gammas:NuDat 18C

Literature and References

[1] - A. G. Artukh, G. F. Gridnev, V. L. Mikheev, V.V. Volkov:
New isotopes ²²O, ²⁰N and ¹⁸C produced in transfer reactions with heavy ions.
In: Nuclear Physics A, 137, 2, (1969), DOI 10.1016/0375-9474(69)90114-6.