26Al-26Mg Ages of Iron Meteorites
Abstract
An exposure age for an iron meteorite can be calculated from measurements of a radioactive nuclide and a stable nuclide that are produced by similar sets of nuclear reactions, provided that the stable nuclide is present with low initial abundance. The standard methods rely on either K-40 (t1/2 = 1.26 Gy), K-39, and K-41 or on a shorter-lived radionuclide and a stable, noble gas isotope. Widely used pairs of this type include Cl-36/Ar-36 and Al-26/Ne-21. Other pairs that may serve the purpose for iron meteorites contain many stable isotopes besides those of K and the noble gases that are produced partly by cosmic rays. We consider here the calculation of exposure ages, t26, from measurements of Al-26 (t1/2 = 0.7 My) and (stable) Mg-26. Ages based on Al-26/Mg-26 ratios, like those based on Cl-36/Ar-36 ratios, are 'buffered' against changes in relative production rates due to shielding because decay of the radioactive nuclide accounts for a good part of the inventory of the stable nuclide.
- Publication:
-
Lunar and Planetary Science Conference
- Pub Date:
- March 1993
- Bibcode:
- 1993LPI....24..647H
- Keywords:
-
- Cosmic Rays;
- Exposure;
- Iron Meteorites;
- Nuclear Reactions;
- Radioactivity;
- Rare Gases;
- Aluminum Isotopes;
- Magnesium Isotopes;
- Potassium 39;
- Potassium 40;
- Astrophysics