Al-26 and O-16 in the early solar system - Clues from meteoritic Al2O3

Abstract

Twenty-six corundum (Al2O3) grains from the Murchison C2 chondrite have been studied by ion probe mass spectrometry, to determine the isotopic record of this highly refractory phase. Mg-26/Mg-24 ranges up to 56 times the solar system ratio, owing to decay of extinct Al- 26, but the initial Al-26/Al-27 ratios (= R0) do not exceed the canonical maximum of 5 x 10(-5) in other meteoritic samples. We conclude that this ratio represents the abundance of live Al-26 in the early solar system, not fossil radiogenic Mg-26 surviving from presolar times. The grains divide into three groups on the basis of Al-26, O-16, Ti, and V content, and Al-26 and O-16 show distinctive correlations (in contrast to all previous studies). This suggests an origin from at least three discrete components, two of which contained live Al-26 (R0 = 5 x 10(-5) and 5 x 10(-6)). Variable R0 values in primitive meteorites apparently reflect mixing of these components rather than decay of Al-26 over a protracted interval and thus are consistent with a short time scale (< 10(6) yr) for the solar nebula.