The isotopic abundance of ²⁶Mg and limits on ²⁶Al in the early solar system

Abstract

The isotopic composition of Mg is investigated in meteoritic, lunar and terrestrial feldspar samples and standard reagents using a mass spectrometer with on-line data processing. Isotopically enriched standards were run demonstrating a resolution of better than five parts in 10⁴ for the ²⁶Mg/²⁴Mg ratio. No ²⁶Mg/²⁴Mg anomalies are found in any samples analyzed to within experimental errors. (These analyses include some samples run by Clarke, de Laeter, Schwarcz and Shane [1] and found by them to have ²⁶Mg/²⁴Mg anomalies of 4–6 parts in 10³ relative to terrestrial values.) There is at the present time no positive evidence indicating the existence of ²⁶Al in the early solar system. From these results, limits are placed on the amount of ²⁶Al (τ½ = 7.4 × 10⁵ yr) and the resulting heating effects in the solar system at the time of crystallization of the meteorites. It is clear that when the meteorites solidified, ²⁶Al was not an important heat source; however, this would not rule out the possibility that a few million years prior to solidification ²⁶Al was a major heat source.

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