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 ¹⁸
Mg with a half-life of 4.0(3.4) zeptoseconds.

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][2] 24.305±0.002 (abridged)[3]
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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: view

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.

External links

• Magnesium isotopes data from The Berkeley Laboratory Isotopes Project's