The stable 27Al is then a surrogate for extinct 26Al. To establish the presence of 26Al in very ancient materials requires demonstrating that samples must contain clear excesses of 26Mg / 24Mg which correlates with the ratio of 27Al/ 24Mg. Thus, any original 26Al in the early Solar System is now extinct. 26Al is only present today in the Solar System materials as the result of cosmic reactions on unshielded materials at an extremely low level. These objects were then found to contain strontium with very low 87Sr/ 86Sr indicating that they were a few million years older than previously analyzed meteoritic material and that this type of material would merit a search for 26Al. This clearly showed a large effect in an abundant element that might be nuclear, possibly from a stellar source. then discovered that the oxygen in these objects was enhanced in 16O by ~5% while the 17O/ 18O was the same as terrestrial. These are very refractory materials and were interpreted as being condensates from a hot solar nebula. The Allende meteorite, which fell in 1969, contained abundant calcium–aluminium-rich inclusions (CAIs). The asteroidal materials that provide meteorite samples were long known to be from the early Solar System. The search for 26Al took place over many years, long after the discovery of the extinct radionuclide 129I (by Reynolds (1960, Physical Review Letters v 4, p 8)) which showed that contribution from stellar sources formed ~10 8 years before the Sun had contributed to the Solar System mix. The life time of 26Al was not then known it was only estimated between 10 4 and 10 6 years. Theoretical considerations suggested that a state of 26Al should exist. Their search was undertaken because hitherto there was no known radioactive isotope of Al that might be useful as a tracer. This conjecture was based on the discovery of 26Al in a Mg target by Simanton, Rightmire, Long & Kohman. This proposal was made well before the general problems of stellar nucleosynthesis of the nuclei were known or understood. He proposed that the heat sources from short lived nuclei from newly formed stars might be the source and identified 26Al as the most likely choice. Urey noted that the naturally occurring long-lived radioactive nuclei ( 40K, 238U, 235U and 232Th) were insufficient heat sources. In considering the known melting of small planetary bodies in the early Solar System, H. The 2011 measurement of the half life of 26mAl is 6346.54 ± 0.46(statistical) ± 0.60(system) milliseconds. The Fermi beta decay half-life of the aluminium-26 metastable state is of interest in the experimental testing of two components of the Standard Model, namely, the conserved-vector-current hypothesis and the required unitarity of the Cabibbo–Kobayashi–Maskawa matrix. The first half-life was determined to be in the range of 10 6 years. After it was theorized that this could be the half-life of a metastable state ( isomer) of aluminium-26, the ground state was produced by bombardment of magnesium-26 and magnesium-25 with deuterons in the cyclotron of the University of Pittsburgh. History īefore 1954, the half-life of aluminium-26 was measured to be 6.3 seconds. This isotope also features in hypotheses regarding the equatorial bulge of Saturn's moon Iapetus. The isotope is believed to provide enough heat to small planetary bodies so as to differentiate their interiors, such as has been the case in the early history of the asteroids 1 Ceres and 4 Vesta. The isotope is mainly produced in supernovas ejecting many radioactive nuclides in the interstellar medium. The observation was made by the HEAO-3 satellite in 1984. The gamma ray emission from the decay of Al-26 at 1809 keV was the first observed gamma emission from the galactic center. Contact with 26Al may result in radiological contamination necessitating special tools for transfer, use, and storage. 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.īecause it is radioactive, it is typically stored behind at least 5 centimetres (2 in) of lead. ĭecay of aluminium-26 also produces gamma rays and x-rays. This is far too short for the isotope to survive as a primordial nuclide, but a small amount of it is produced by collisions of atoms with cosmic ray protons. Isotope of aluminium Aluminium-26, 26Al GeneralĪluminium-26 ( 26Al, Al-26) is a radioactive isotope of the chemical element aluminium, decaying by either positron emission or electron capture to stable magnesium-26.
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