Isotopes of aluminium

Aluminium (Al) has 22 known isotopes from 21Al to 42Al and 4 known isomers. Only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2 × 105 y) occur naturally, however 27Al has a natural abundance of 99.9+ %. Other than 26Al, all radioisotopes have half-lives under 7 minutes, most under a second. Standard atomic mass is 26.9815386(8) u. 26Al 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 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.

Cosmogenic Aluminium-26 was first applied 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.[1]

Contents

Table

nuclide
symbol		 Z(p) N(n)  
isotopic mass (u)
 		 half-life decay
mode(s)[2][n 1]		 daughter
isotope(s)[n 2]		 nuclear
spin		 representative
isotopic
composition
(mole fraction)		 range of natural
variation
(mole fraction)
excitation energy
21Al 13 8 21.02804(32)# <35 ns p 20Mg 1/2+#
22Al 13 9 22.01952(10)# 59(3) ms β+ (96.7%) 22Mg (3)+
β+, 2p (2.5%) 20Ne
β+, p (0.8%) 21Na
23Al 13 10 23.007267(20) 470(30) ms β+ (92%) 23Mg 5/2+#
β+, p (8%) 22Na
23mAl ~0.35 s #79
24Al 13 11 23.9999389(30) 2.053(4) s β+ (99.95%) 24Mg 4+
β+, α (.0349%) 20Ne
β+, p (.0159%) 23Na
24mAl 425.8(1) keV 131.3(25) ms IT (82%) 24Al 1+
β+ (18%) 24Mg
β+, α 20Ne
25Al 13 12 24.9904281(5) 7.183(12) s β+ 25Mg 5/2+
26Al[n 3] 13 13 25.98689169(6) 7.17(24)×105 a β+ 26Mg 5+ Trace[n 4]
26mAl 228.305(13) keV 6.3452(19) s β+ 26Mg 0+
27Al 13 14 26.98153863(12) STABLE 5/2+ 1.0000
28Al 13 15 27.98191031(14) 2.2414(12) min β- 28Si 3+
29Al 13 16 28.9804450(13) 6.56(6) min β- 29Si 5/2+
30Al 13 17 29.982960(15) 3.60(6) s β- 30Si 3+
31Al 13 18 30.983947(22) 644(25) ms β- (98.4%) 31Si (3/2,5/2)+
β-, n (1.6%) 30Si
32Al 13 19 31.98812(9) 31.7(8) ms β- (99.3%) 32Si 1+
β-, n (.7%) 31Si
32mAl 955.7(4) keV 200(20) ns (4+)
33Al 13 20 32.99084(8) 41.7(2) ms β- (91.5%) 33Si (5/2+)#
β-, n (8.5%) 32Si
34Al 13 21 33.99685(12) 56.3(5) ms β- (87.5%) 34Si 4-#
β-, n (12.5%) 33Si
35Al 13 22 34.99986(19) 38.6(4) ms β- (74%) 35Si 5/2+#
β-, n (26%) 33Si
36Al 13 23 36.00621(23) 90(40) ms β- (69%) 36Si
β-, n (31%) 35Si
37Al 13 24 37.01068(36) 10.7(13) ms β- 37Si 3/2+
38Al 13 25 38.01723(78) 7.6(6) ms β- 38Si
39Al 13 26 39.02297(158) 7.6(16) ms β- 39Si 3/2+#
40Al 13 27 40.03145(75)# 10# ms [>260 ns]
41Al 13 28 41.03833(86)# 2# ms [>260 ns] 3/2+#
42Al 13 29 42.04689(97)# 1 ms
  1. ^ Abbreviations:
    IT: Isomeric transition
  2. ^ Bold for stable isotopes
  3. ^ Used in radiodating events early in the Solar System's history and meteorites
  4. ^ cosmogenic

Notes

See also

Book: Aluminium
Wikipedia books are collections of articles that can be downloaded or ordered in print.


References

  1. ^ R. T. Dodd. Thunderstones and Shooting Stars. pp. 89–90. ISBN 0-674-89137-6. 
  2. ^ http://www.nucleonica.net/unc.aspx

External links

Isotopes of magnesium Isotopes of aluminium Isotopes of silicon
Index to isotope pages · Table of nuclides