Aluminium-26

Aluminium-26, ²⁶Al, is a radioactive isotope of the chemical element aluminium, decaying by either of the modes beta-plus or electron capture, both resulting in the stable nuclide magnesium-26. The half-life of ²⁶Al is 7.17×10⁵ years. This is far too short for the isotope to survive to the present, but a small amount of the nuclide is produced by collisions of argon atoms with cosmic ray protons.

Aluminium-26 also emits gamma rays and X-rays. The x-rays and Auger electrons are emitted by the excited atomic shell of the daughter ²⁶Mg after the electron capture which typically leaves a hole in one of the lower sub-shells.

Because it is radioactive it should be stored behind at least 5 cm (2 in) of lead and special tools should be used for transfer, use, and storage. Contact with ²⁶Al may result in radiological contamination.

Aluminium-26 can be used to calculate the terrestrial age of meteorites. After the breakup of the meteorite parent body, it will be bombarded by cosmic rays, which will saturate it in aluminium-26. After falling to earth, ²⁶Al production ceases, which means that the amount of ²⁶Al in the sample can be used to calculate the date the meteorite fell to earth.

The gamma emission at 1809 keV was the first observed gamma emission from the galactic center. The observation was made by the HEAO-3 satellite in 1984.

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