Isotopes of magnesium

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 19
Mg with a half-life of 5(3) picoseconds, though the half-life of similarly unbound 18
Mg has not been measured.

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]

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[6]
 Z N Isotopic mass (Da)[7]
[n 1]		 Half-life
[n 2]		 Decay
mode
[n 3]		 Daughter
isotope
[n 4]		 Spin and
parity
[n 5][n 2]		 Natural abundance (mole fraction)
Normal proportion Range of variation
18
Mg[8]		 12 6 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[9] 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. # – 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. Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide.

References
  1. 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. Half-life, decay mode, nuclear spin, and isotopic composition is sourced in:
    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.
  7. 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.
  8. 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.
  9. 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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