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)
	[24.304, 24.307] 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+	[0.7888, 0.7905]
25 Mg	12	13	24.98583697(5)	Stable			5/2+	[0.09988, 0.10034]
26 Mg	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 ?	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 ?	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 ?	34 Al ?
37 Mg	12	25	37.03029(75)	8(4) ms	β− ?	37 Al ?	(3/2−)
					β−n ?	36 Al ?
					β−2n ?	35 Al ?
38 Mg	12	26	38.03658(54)#	3.1(4 (stat), 2 (sys)) ms	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− ?	40 Al ?	0+
					β−n ?	39 Al ?
					β−2n ?	38 Al ?
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External links

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