page_title: Isotopes of aluminium
section_title: Aluminium-26
hierarchical_section_title: Isotopes of aluminium / Aluminium-26
caption_attribution_description: English: The decay scheme of Aluminum-26 and metastable Aluminum-26m to Mg26 and its excited states. Al-26m decays to a positron and Mg-26. The Al-26 ground state only decays to excited states of Mg-26 (Mg-26*), by way of electron capture or positron emission. The excited states of Mg-26 gamma decay to the ground state almost instantly.
context_page_description: Aluminium or aluminum has 22 known isotopes from ²²Al to ⁴³Al and 4 known isomers. Only ²⁷Al and ²⁶Al occur naturally, however ²⁷Al comprises nearly all natural aluminium. Other than ²⁶Al, all radioisotopes have half-lives under 7 minutes, most under a second. The standard atomic weight is 26.9815385. 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. ²⁶Al has also played a significant role in the study of meteorites.
context_section_description: 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.
caption: The decay level scheme for 26Al and 26mAl to 26Mg.[4][5]
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