# Isotopes of magnesium

Magnesium ($_{12}$Mg) 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 $^{40}$Mg in 2019 showed the unexpected difference in its nuclear structure, compared to the lighter neighboring isotopes.

## List of isotopes

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