Isotopes of aluminium

or aluminum 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.
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.

List of isotopes

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.