Magnesium-18

Properties and data of the isotope ¹⁸Mg.

Contents

Magnesium-18 is a radioisotope of the chemical element magnesium, which has 6 neutrons in its atomic nucleus in addition to the element-specific 12 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 ¹⁸Mg is exclusively for academic purposes.

The first observation of the extremely proton-rich isotope was first reported in 2021 [1].

Magnesium-18 decays from the ground state by two consecutive two-proton emissions (2p) via the intermediate nucleus neon-16 to oxygen-14 [2].

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

General data

Name of the isotope:Magnesium-18; Mg-18Symbol:¹⁸Mg or 1812MgMass number A:18 (= number of nucleons)Atomic number Z:12 (= number of protons)Neutrons N:6Isotopic mass:18 u (atomic weight of Magnesium-18)Nuclide mass:17.9934171 u (calculated nuclear mass without electrons)Mass excess:0 MeVMass defect:0.14588988 u (per nucleus)Nuclear binding energy:135.89554788 MeV (per nucleus)
7.54975266 MeV (average binding energy per nucleon)Half-life:Decay constant λ:1.732867951399 × 10⁺²⁰ s^-1Specific activity α:5.797541608333 × 10⁺⁴² Bq g^-1
1.566903137387 × 10⁺³² Ci g^-1Spin and parity:
(nuclear angular momentum)0+Mirror nucleus:Carbon-18Year of discovery:2021

Radioactive Decay

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
2p	¹⁶Ne	100 %

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 6) and isobaric (same nucleon number A = 18) with Magnesium-18. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 6	Isobar A = 18
1	⁷H
2	⁸He
3	⁹Li
4	¹⁰Be
5	¹¹B	¹⁸B
6	¹²C	¹⁸C
7	¹³N	¹⁸N
8	¹⁴O	¹⁸O
9	¹⁵F	¹⁸F
10	¹⁶Ne	¹⁸Ne
11	¹⁷Na	¹⁸Na
12	¹⁸Mg	¹⁸Mg

Literature and References

[1] - Y. Jin et al.:
First Observation of the Four-Proton Unbound Nucleus ¹⁸Mg.
In: Physical Review Letters, 127, 262502, (2021), DOI 10.1103/PhysRevLett.127.262502.

[2] - Long Zhou et al.:
Structure and 2p decay mechanism of ¹⁸Mg.
In: Nuclear Science and Techniques, 35, 107, (2024), DOI 10.1007/s41365-024-01479-1.