# Isotopes of aluminium

Aluminium or aluminum ($_{13}$Al) has 23 known isotopes from $^{21}$Al to $^{43}$Al and 4 known isomers. Only $^{27}$Al (stable isotope) and $^{26}$Al (radioactive isotope, t$_{1/2}$ = 7.2×10$^5$ y) occur naturally, however $^{27}$Al comprises nearly all natural aluminium. Other than $^{26}$Al, all radioisotopes have half-lives under 7 minutes, most under a second. The standard atomic weight is 26.9815385(7). $^{26}$Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of $^{26}$Al to $^{10}$Be has been used to study the role of sediment transport, deposition, and storage, as well as burial times, and erosion, on 10$^5$ to 10$^6$ year time scales. $^{26}$Al has also played a significant role in the study of meteorites.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Isotopic abundance |
| Isotopic abundance |||
| $^{21}$Al | 13 | 8 | 21.0278(13) | >1.1 zs | p | $^{20}$Mg | (5/2+) | |
| $^{22}$Al | 13 | 9 | 22.01942310(32) | 91.1(5) ms | β$^+$, p (55%) | $^{21}$Na | (4)+ | |
| $^{22}$Al | 13 | 9 | 22.01942310(32) | 91.1(5) ms | β$^+$ (44%) | $^{22}$Mg | (4)+ | |
| $^{22}$Al | 13 | 9 | 22.01942310(32) | 91.1(5) ms | β$^+$, 2p (1.10%) | $^{20}$Ne | (4)+ | |
| $^{22}$Al | 13 | 9 | 22.01942310(32) | 91.1(5) ms | β$^+$, α (0.038%) | $^{18}$Ne | (4)+ | |
| $^{23}$Al | 13 | 10 | 23.00724435(37) | 446(6) ms | β$^+$ (98.78%) | $^{23}$Mg | 5/2+ | |
| $^{23}$Al | 13 | 10 | 23.00724435(37) | 446(6) ms | β$^+$, p (1.22%) | $^{22}$Na | 5/2+ | |
| $^{24}$Al | 13 | 11 | 23.99994760(24) | 2.053(4) s | β$^+$ (99.96%) | $^{24}$Mg | 4+ | |
| $^{24}$Al | 13 | 11 | 23.99994760(24) | 2.053(4) s | β$^+$, α (0.035%) | $^{20}$Ne | 4+ | |
| $^{24}$Al | 13 | 11 | 23.99994760(24) | 2.053(4) s | β$^+$, p (0.0016%) | $^{23}$Na | 4+ | |
| $^{24m}$Al | 425.8(1) keV | 425.8(1) keV | 425.8(1) keV | 130(3) ms | IT (82.5%) | $^{24}$Al | 1+ | |
| $^{24m}$Al | 425.8(1) keV | 425.8(1) keV | 425.8(1) keV | 130(3) ms | β$^+$ (17.5%) | $^{24}$Mg | 1+ | |
| $^{24m}$Al | 425.8(1) keV | 425.8(1) keV | 425.8(1) keV | 130(3) ms | β$^+$, α (0.028%) | $^{20}$Ne | 1+ | |
| $^{25}$Al | 13 | 12 | 24.990428308(69) | 7.1666(23) s | β$^+$ | $^{25}$Mg | 5/2+ | |
| $^{26}$Al | 13 | 13 | 25.986891876(71) | 7.17(24)×10$^5$ y | β$^+$ (85%) | $^{26}$Mg | 5+ | Trace |
| $^{26}$Al | 13 | 13 | 25.986891876(71) | 7.17(24)×10$^5$ y | EC (15%) | $^{26}$Mg | 5+ | Trace |
| $^{26m}$Al | 228.306(13) keV | 228.306(13) keV | 228.306(13) keV | 6.3460(5) s | β$^+$ | $^{26}$Mg | 0+ | |
| $^{27}$Al | 13 | 14 | 26.981538408(50) | Stable | Stable | Stable | 5/2+ | 1.0000 |
| $^{28}$Al | 13 | 15 | 27.981910009(52) | 2.245(5) min | β$^−$ | $^{28}$Si | 3+ | |
| $^{29}$Al | 13 | 16 | 28.98045316(37) | 6.56(6) min | β$^−$ | $^{29}$Si | 5/2+ | |
| $^{30}$Al | 13 | 17 | 29.9829692(21) | 3.62(6) s | β$^−$ | $^{30}$Si | 3+ | |
| $^{31}$Al | 13 | 18 | 30.9839498(24) | 644(25) ms | β$^−$ (>98.4%) | $^{31}$Si | 5/2+ | |
| $^{31}$Al | 13 | 18 | 30.9839498(24) | 644(25) ms | β$^−$, n (<1.6%) | $^{30}$Si | 5/2+ | |
| $^{32}$Al | 13 | 19 | 31.9880843(77) | 32.6(5) ms | β$^−$ (99.3%) | $^{32}$Si | 1+ | |
| $^{32}$Al | 13 | 19 | 31.9880843(77) | 32.6(5) ms | β$^−$, n (0.7%) | $^{31}$Si | 1+ | |
| $^{32m}$Al | 956.6(5) keV | 956.6(5) keV | 956.6(5) keV | 200(20) ns | IT | $^{32}$Al | (4+) | |
| $^{33}$Al | 13 | 20 | 32.9908777(75) | 41.46(9) ms | β$^−$ (91.5%) | $^{33}$Si | 5/2+ | |
| $^{33}$Al | 13 | 20 | 32.9908777(75) | 41.46(9) ms | β$^−$, n (8.5%) | $^{32}$Si | 5/2+ | |
| $^{34}$Al | 13 | 21 | 33.9967819(23) | 53.73(13) ms | β$^−$ (74%) | $^{34}$Si | 4− | |
| $^{34}$Al | 13 | 21 | 33.9967819(23) | 53.73(13) ms | β$^−$, n (26%) | $^{33}$Si | 4− | |
| $^{34m}$Al | 46.4(17) keV | 46.4(17) keV | 46.4(17) keV | 22.1(2) ms | β$^−$ (89%) | $^{34}$Si | 1+ | |
| $^{34m}$Al | 46.4(17) keV | 46.4(17) keV | 46.4(17) keV | 22.1(2) ms | β$^−$, n (11%) | $^{33}$Si | 1+ | |
| $^{35}$Al | 13 | 22 | 34.9997598(79) | 38.16(21) ms | β$^−$ (64.2%) | $^{35}$Si | (5/2+,3/2+) | |
| $^{35}$Al | 13 | 22 | 34.9997598(79) | 38.16(21) ms | β$^−$, n (35.8%) | $^{34}$Si | (5/2+,3/2+) | |
| $^{36}$Al | 13 | 23 | 36.00639(16) | 90(40) ms | β$^−$ (>69%) | $^{36}$Si | | |
| $^{36}$Al | 13 | 23 | 36.00639(16) | 90(40) ms | β$^−$, n (<31%) | $^{35}$Si | | |
| $^{37}$Al | 13 | 24 | 37.01053(19) | 11.4(3) ms | β$^−$, n (52%) | $^{36}$Si | 5/2+# | |
| $^{37}$Al | 13 | 24 | 37.01053(19) | 11.4(3) ms | β$^−$ (<47%) | $^{37}$Si | 5/2+# | |
| $^{37}$Al | 13 | 24 | 37.01053(19) | 11.4(3) ms | β$^−$, 2n (>1%) | $^{35}$Si | 5/2+# | |
| $^{38}$Al | 13 | 25 | 38.01768(16)# | 9.0(7) ms | β$^−$, n (84%) | $^{37}$Si | 0−# | |
| $^{38}$Al | 13 | 25 | 38.01768(16)# | 9.0(7) ms | β$^−$ (16%) | $^{38}$Si | 0−# | |
| $^{39}$Al | 13 | 26 | 39.02307(32)# | 7.6(16) ms | β$^−$, n (97%) | $^{38}$Si | 5/2+# | |
| $^{39}$Al | 13 | 26 | 39.02307(32)# | 7.6(16) ms | β$^−$ (3%) | $^{39}$Si | 5/2+# | |
| $^{40}$Al | 13 | 27 | 40.03094(32)# | 5.7(3 (stat), 2 (sys)) ms | β$^−$, n (64%) | $^{39}$Si | | |
| $^{40}$Al | 13 | 27 | 40.03094(32)# | 5.7(3 (stat), 2 (sys)) ms | β$^−$, 2n (20%) | $^{38}$Si | | |
| $^{40}$Al | 13 | 27 | 40.03094(32)# | 5.7(3 (stat), 2 (sys)) ms | β$^−$ (16%) | $^{40}$Si | | |
| $^{41}$Al | 13 | 28 | 41.03713(43)# | 3.5(8 (stat), 4 (sys)) ms | β$^−$, n (86%) | $^{40}$Si | 5/2+# | |
| $^{41}$Al | 13 | 28 | 41.03713(43)# | 3.5(8 (stat), 4 (sys)) ms | β$^−$, 2n (11%) | $^{39}$Si | 5/2+# | |
| $^{41}$Al | 13 | 28 | 41.03713(43)# | 3.5(8 (stat), 4 (sys)) ms | β$^−$ (3%) | $^{41}$Si | 5/2+# | |
| $^{42}$Al | 13 | 29 | 42.04508(54)# | 3# ms [>170 ns] | | | | |
| $^{43}$Al | 13 | 30 | 43.05182(64)# | 4# ms [>170 ns] | β$^−$? | $^{43}$Si | 5/2+# | |
| This table header & footer: view |||||||||
* ↑ $^m$Al – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* ↑ Modes of decay: IT:Isomeric transition
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Used in radiodating events early in the Solar System's history and meteorites
* ↑ cosmogenic

## Aluminium-26

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 $^{26}$Al production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further $^{26}$Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that $^{26}$Al was relatively abundant at the time of formation of our planetary system. Most meteoriticists believe that the energy released by the decay of $^{26}$Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.