aluminum26

Aluminum-26 (26Al) is a radioactive isotope of aluminum with mass number 26 and atomic number 13. It has a half-life of about 717,000 years and decays primarily by beta-plus decay and electron capture to magnesium-26, often accompanied by the emission of a 1.809 MeV gamma ray as the daughter nucleus de-excites.

Natural occurrence and production of 26Al are limited on Earth, but it is produced in space. It is formed in massive stars and during supernova explosions, and it is also created by cosmic ray spallation in the interstellar medium. The isotope is observed in the galaxy through its characteristic gamma-ray emission, which maps regions of ongoing nucleosynthesis.

Astrophysical and cosmochemical significance is wide. The 1.809 MeV gamma-ray line provides direct evidence of ongoing nucleosynthesis in the Milky Way. In the early solar system, the presence of 26Al is inferred from excess 26Mg in primitive meteorites, leading to a canonical initial 26Al/27Al ratio of about 5 × 10^-5. This short-lived radionuclide is thought to have contributed significant heat during the early differentiation and melting of planetesimals.

Applications and measurements rely on the 26Al-27Al system as a chronometer for early solar system events and on gamma-ray observations for studying its distribution in the Galaxy. Its study connects stellar nucleosynthesis, planetary formation, and meteoritic chronology.

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