Isotopes of aluminium

Aluminium or aluminum (₁₃Al) has one stable isotope, ²⁷Al, comprising all natural aluminium. The radioactive ²⁶Al, with half-life 717,000 years, occurs in traces from cosmic-ray spallation of argon in the atmosphere.

Isotopes of aluminium (₁₃Al)

Main isotopes[1] Decay Isotope abun­dance half-life (t1/2) mode pro­duct 26Al trace 7.17×105 y β+ 26Mg 27Al 100% stable
Standard atomic weight Ar°(Al)
	26.9815384±0.0000003[2] 26.982±0.001 (abridged)[3]
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Other than ²⁶Al, there are 22 known synthetic radioisotopes from ²⁰Al to ⁴³Al, and 4 known metastable states; all have half-lives under 7 minutes, most under a second.

²⁶Al is an extinct radionuclide and has received attention as such, being used in the study of meteorites. Its terrestrial occurrence has also found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of ²⁶Al to ¹⁰Be has been used to study the role of sediment transport, deposition, and storage, as well as burial times, and erosion, on 10⁵ to 10⁶ year time scales.^[4]

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[5] [n 2][n 3]	Half-life[1]	Decay mode[1] [n 4]	Daughter isotope [n 5]	Spin and parity[1] [n 6][n 7]	Isotopic abundance
	Excitation energy[n 7]
20Al[6]	13	7	20.04326(13)	>1.1 zs	p	19Mg	(1−)
21Al[7]	13	8	21.0278(13)	>1.1 zs	p	20Mg	(5/2+)
22Al	13	9	22.01942310(32)[8]	91.1(5) ms	β+, p (55%)	21Na	(4)+
					β+ (44%)	22Mg
					β+, 2p (1.10%)	20Ne
					β+, α (0.038%)	18Ne
23Al	13	10	23.00724435(37)	446(6) ms	β+ (98.78%)	23Mg	5/2+
					β+, p (1.22%)	22Na
24Al	13	11	23.99994760(24)	2.053(4) s	β+ (99.96%)	24Mg	4+
					β+, α (0.035%)	20Ne
					β+, p (0.0016%)	23Na
24mAl	425.8(1) keV			130(3) ms	IT (82.5%)	24Al	1+
					β+ (17.5%)	24Mg
					β+, α (0.028%)	20Ne
25Al	13	12	24.990428308(69)	7.1666(23) s	β+	25Mg	5/2+
26Al[n 8]	13	13	25.986891876(71)	7.17(24)×105 y	β+ (85%)	26Mg	5+	Trace[n 9]
					EC (15%)[9]
26mAl	228.306(13) keV			6.3460(5) s	β+	26Mg	0+
27Al	13	14	26.981538408(50)	Stable			5/2+	1.0000
28Al	13	15	27.981910009(52)	2.245(5) min	β−	28Si	3+
29Al	13	16	28.98045316(37)	6.56(6) min	β−	29Si	5/2+
30Al	13	17	29.9829692(21)	3.62(6) s	β−	30Si	3+
31Al	13	18	30.9839498(24)	644(25) ms	β− (>98.4%)	31Si	5/2+
					β−, n (<1.6%)	30Si
32Al	13	19	31.9880843(77)	32.6(5) ms	β− (99.3%)	32Si	1+
					β−, n (0.7%)	31Si
32mAl	956.6(5) keV			200(20) ns	IT	32Al	(4+)
33Al	13	20	32.9908777(75)	41.46(9) ms	β− (91.5%)	33Si	5/2+
					β−, n (8.5%)	32Si
34Al	13	21	33.9967819(23)	53.73(13) ms	β− (74%)	34Si	4−
					β−, n (26%)	33Si
34mAl	46.4(17) keV			22.1(2) ms	β− (89%)	34Si	1+
					β−, n (11%)	33Si
35Al	13	22	34.9997598(79)	38.16(21) ms	β− (64.2%)	35Si	(5/2+,3/2+)
					β−, n (35.8%)	34Si
36Al	13	23	36.00639(16)	90(40) ms	β− (>69%)	36Si
					β−, n (<31%)	35Si
37Al	13	24	37.01053(19)	11.4(3) ms	β−, n (52%)	36Si	5/2+#
					β− (<47%)	37Si
					β−, 2n (>1%)	35Si
38Al	13	25	38.01768(16)#	9.0(7) ms	β−, n (84%)	37Si	0−#
					β− (16%)	38Si
39Al	13	26	39.02307(32)#	7.6(16) ms	β−, n (97%)	38Si	5/2+#
					β− (3%)	39Si
40Al	13	27	40.03094(32)#	5.7(3 (stat), 2 (sys)) ms[10]	β−, n (64%)	39Si
					β−, 2n (20%)	38Si
					β− (16%)	40Si
41Al	13	28	41.03713(43)#	3.5(8 (stat), 4 (sys)) ms[10]	β−, n (86%)	40Si	5/2+#
					β−, 2n (11%)	39Si
					β− (3%)	41Si
42Al	13	29	42.04508(54)#	3# ms [>170 ns]
43Al	13	30	43.05182(64)#	4# ms [>170 ns]	β−?	43Si	5/2+#
This table header & footer: view

1. ^mAl – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Modes of decay:

   IT:	Isomeric transition

5. Bold symbol as daughter – Daughter product is stable.
6. ( ) spin value – Indicates spin with weak assignment arguments.
7. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
8. Used in radiodating events early in the Solar System's history and meteorites
9. cosmogenic

Aluminium-26

Main article: Aluminium-26

The decay level scheme for ²⁶Al and ^26mAl to ²⁶Mg.^[11][12]

Cosmogenic aluminium-26 was first described in studies of the Moon and meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial ²⁶Al production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further ²⁶Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that ²⁶Al was relatively abundant at the time of formation of our planetary system. Most meteoriticists believe that the energy released by the decay of ²⁶Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.^[13]

See also

Daughter products other than aluminum

• Isotopes of silicon
• Isotopes of magnesium
• Isotopes of sodium
• Isotopes of neon