Isotopes of magnesium (12Mg)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
24Mg 79% stable
25Mg 10% stable
26Mg 11% stable
Standard atomic weight Ar°(Mg)
  • [24.304, 24.307]
  • 24.305±0.002 (abridged)[2][3]

Magnesium (12Mg) naturally occurs in three stable isotopes: 24
Mg, 25
Mg, and 26
Mg. There are 19 radioisotopes that have been discovered, ranging from 18
Mg to 40
Mg (with the exception of 39
Mg). The longest-lived radioisotope is 28
Mg with a half-life of 20.915(9) h. The lighter isotopes mostly decay to isotopes of sodium while the heavier isotopes decay to isotopes of aluminium. The shortest-lived is proton-unbound 18
Mg with a half-life of 4.0(3.4) zeptoseconds.

A precise measurement of the neutron-rich 40Mg in 2019 showed the unexpected difference in its nuclear structure, compared to the lighter neighboring isotopes.[4][5]

The abundances of the naturally occurring isotopes of magnesium.

List of isotopes

Nuclide
 Z N Isotopic mass (Da)[6]
[n 1]		 Half-life[1]
[n 2]		 Decay
mode[1]
[n 3]		 Daughter
isotope
[n 4]		 Spin and
parity[1]
[n 5][n 2]		 Natural abundance (mole fraction)
Normal proportion[1] Range of variation
18
Mg[7]		 12 6 4.0(3.4) zs 2p 16
Ne		 0+
19
Mg		 12 7 19.034180(60) 5(3) ps 2p 17
Ne		 1/2−#
20
Mg 		12 8 20.0187631(20) 90.4(5) ms β+ (69.7(1.2)%) 20
Na		 0+
β+p (30.3(1.2)%) 19
Ne
21
Mg 		12 9 21.0117058(8) 120.0(4) ms β+ (79.8(2.1)%) 21
Na		 5/2+
β+p (20.1(2.1)%) 20
Ne
β+α (0.116(18)%) 17
F
β+pα (0.016(3)%) 16
O
22
Mg 		12 10 21.99957060(17) 3.8745(7) s β+ 22
Na		 0+
23
Mg 		12 11 22.99412377(3) 11.3039(32) s β+ 23
Na		 3/2+
24
Mg 		12 12 23.985041689(14) Stable 0+ [0.7888, 0.7905]
25
Mg 		12 13 24.98583697(5) Stable 5/2+ [0.09988, 0.10034]
26
Mg[n 6] 		12 14 25.98259297(3) Stable 0+ [0.1096, 0.1109]
27
Mg 		12 15 26.98434065(5) 9.435(27) min β− 27
Al		 1/2+
28
Mg 		12 16 27.98387543(28) 20.915(9) h β− 28
Al		 0+
29
Mg 		12 17 28.9886072(4) 1.30(12) s β− 29
Al		 3/2+
30
Mg 		12 18 29.9904655(14) 317(4) ms β− (> 99.94%) 30
Al		 0+
β−n (< 0.06%) 29
Al
31
Mg 		12 19 30.996648(3) 270(2) ms β− (93.8(1.9)%) 31
Al		 1/2+
β−n (6.2(1.9)%) 30
Al
32
Mg 		12 20 31.999110(4) 80.4(4) ms β− (94.5(5)%) 32
Al		 0+
β−n (5.5(5)%) 31
Al
33
Mg 		12 21 33.0053279(29) 92.0(1.2) ms β− (86(2)%) 33
Al		 3/2−
β−n (14(2)%) 32
Al
β−2n ?[n 7] 31
Al ?
34
Mg 		12 22 34.008935(7) 44.9(4) ms β− (> 78.9(7.0)%) 34
Al		 0+
β−n (21(7)%) 33
Al
β−2n (< 0.1%) 32
Al
35
Mg 		12 23 35.01679(29) 11.3(6) ms β−n (52(46)%) 34
Al		 (3/2−, 5/2−)
β− (48(46)%) 35
Al
β−2n ?[n 7] 33
Al ?
36
Mg 		12 24 36.02188(74) 3.9(1.3) ms β− (52(12)%) 36
Al		 0+
β−n (48(12)%) 35
Al
β−2n ?[n 7] 34
Al ?
37
Mg 		12 25 37.03029(75) 8(4) ms β− ?[n 7] 37
Al ?		 (3/2−)
β−n ?[n 7] 36
Al ?
β−2n ?[n 7] 35
Al ?
38
Mg 		12 26 38.03658(54)# 3.1(4 (stat), 2 (sys)) ms[8] β−n (81%) 37
Al		 0+
β− (9%) 38
Al
β−2n (9%) 36
Al
40
Mg 		12 28 40.05319(54)# 1# ms [> 170 ns] β− ?[n 7] 40
Al ?		 0+
β−n ?[n 7] 39
Al ?
β−2n ?[n 7] 38
Al ?
This table header & footer:
  1. ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  3. ↑ Modes of decay:
    n:Neutron emission
    p:Proton emission
  4. ↑ Bold symbol as daughter – Daughter product is stable.
  5. ↑ ( ) spin value – Indicates spin with weak assignment arguments.
  6. ↑ Used in radiodating events early in the Solar System's history
  7. 1 2 3 4 5 6 7 8 9 Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide.

References

  1. 1 2 3 4 5 Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. ↑ "Standard Atomic Weights: Magnesium". CIAAW. 2011.
  3. ↑ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. ↑ glennroberts (2019-02-07). "New Measurements of Exotic Magnesium Suggest Surprising Shape-Shift". Berkeley Lab News Center. Retrieved 2023-09-10.
  5. ↑ "NP A Change in Structure for a S... | U.S. DOE Office of Science(SC)". science.osti.gov. 2019-08-01. Retrieved 2023-09-10.
  6. ↑ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
  7. ↑ Jin, Y.; et al. (2021). "First observation of the four-proton unbound nucleus 18Mg". Physical Review Letters. 127 (262502): 262502. doi:10.1103/PhysRevLett.127.262502. OSTI 1837749. PMID 35029460. S2CID 245434485.
  8. ↑ Crawford, H. L.; Tripathi, V.; Allmond, J. M.; et al. (2022). "Crossing N = 28 toward the neutron drip line: first measurement of half-lives at FRIB". Physical Review Letters. 129 (212501): 212501. Bibcode:2022PhRvL.129u2501C. doi:10.1103/PhysRevLett.129.212501. PMID 36461950. S2CID 253600995.
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