Isotopes of magnesium

Isotopes of magnesium (12Mg)
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
24Mg 79% stable
25Mg 10% stable
26Mg 11% stable
Standard atomic weight Ar°(Mg)
  • [24.30424.307]
  • 24.305±0.002 (abridged)

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.

The abundances of the naturally occurring isotopes of magnesium.

List of isotopes

Nuclide
Z N Isotopic mass (Da)
Half-life
Decay
mode

Daughter
isotope

Spin and
parity
Natural abundance (mole fraction)
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+
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+ [0.78880.7905]
25
Mg
12 13 24.98583697(5) Stable 5/2+ [0.099880.10034]
26
Mg
12 14 25.98259297(3) Stable 0+ [0.10960.1109]
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+
βn (< 0.06%) 29
Al
31
Mg
12 19 30.996648(3) 270(2) ms β (93.8(1.9)%) 31
Al
1/2+
βn (6.2(1.9)%) 30
Al
32
Mg
12 20 31.999110(4) 80.4(4) ms β (94.5(5)%) 32
Al
0+
βn (5.5(5)%) 31
Al
33
Mg
12 21 33.0053279(29) 92.0(1.2) ms β (86(2)%) 33
Al
3/2−
βn (14(2)%) 32
Al
β2n ? 31
Al
 ?
34
Mg
12 22 34.008935(7) 44.9(4) ms β (> 78.9(7.0)%) 34
Al
0+
βn (21(7)%) 33
Al
β2n (< 0.1%) 32
Al
35
Mg
12 23 35.01679(29) 11.3(6) ms βn (52(46)%) 34
Al
(3/2−, 5/2−)
β (48(46)%) 35
Al
β2n ? 33
Al
 ?
36
Mg
12 24 36.02188(74) 3.9(1.3) ms β (52(12)%) 36
Al
0+
βn (48(12)%) 35
Al
β2n ? 34
Al
 ?
37
Mg
12 25 37.03029(75) 8(4) ms β ? 37
Al
 ?
(3/2−)
βn ? 36
Al
 ?
β2n ? 35
Al
 ?
38
Mg
12 26 38.03658(54)# 3.1(4 (stat), 2 (sys)) ms βn (81%) 37
Al
0+
β (9%) 38
Al
β2n (9%) 36
Al
40
Mg
12 28 40.05319(54)# 1# ms [> 170 ns] β ? 40
Al
 ?
0+
βn ? 39
Al
 ?
β2n ? 38
Al
 ?
This table header & footer:
  1. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. ^ a b # – 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. ^ a b c d e f g h i Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide.

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