Oxygen-18

Properties and data of the isotope ¹⁸O.

Contents

Oxygen-18 is a stable isotope of the chemical element oxygen, which has 10 neutrons in its atomic nucleus in addition to the element-specific 8 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 18. According to a report from 1929, ¹⁸O was identified as a distinct oxygen isotope based on the absorption bands of atmospheric oxygen [1].

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

General data

Name of the isotope:Oxygen-18; O-18Symbol:¹⁸O or 188OMass number A:18 (= number of nucleons)Atomic number Z:8 (= number of protons)Neutrons N:10Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):1.25 (= neutron-proton ratio)Neutron excess (N-Z):2Isotopic mass:17.999159613(5) u (atomic weight of Oxygen-18)Nuclide mass:17.994771 u (calculated nuclear mass without electrons)Mass excess:-0.78282 MeVMass defect:0.150089803 u (per nucleus)Nuclear binding energy:139.80775096 MeV (per nucleus)
7.76709728 MeV (average binding energy per nucleon)Separation energy:S_N = 8.0453702(10) MeV (first neutron)
S_P = 15.942(15) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)0+Isobaric spin: 1Charge radius:2.7726(56) femtometer fmMirror nucleus:Neon-18Year of discovery:1929

Parent Nuclides

Direct parent isotopes are: ¹⁸N, ¹⁸F.

Occurrence

Comparison of the natural Oxygen isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Oxygen Isotopic mixture	15.999 u	100 %
Isotope ¹⁶O	15.994914619(1) u	99.757 % [99.738 - 99.776 %]	stable	0+
Isotope ¹⁷O	16.999131757(5) u	0.03835(96) % [0.0367 - 0.0400 %]	stable	5/2+
Isotope ¹⁸O	17.999159613(5) u	0.2045 % [0.187 - 0.222 %]	stable	0+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 10) and isobaric (same nucleon number A = 18) with Oxygen-18. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

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

External data and identifiers

Adopted Levels, Gammas:NuDat 18O

Literature and References

[1] - W. F. Giauque, H. L. Johnston:
An isotope of oxygen, mass 18. Interpretation of the atmospheric absorption bands.
In: Journal of the American Chemical Society, 51, 5, (1929), DOI 10.1021/ja01380a018.