Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion
We have studied the Mg and Ca isotopic compositions of an unusual Allende inclusion dominated by hibonite, which is the most refractory and possibly the most primitive major oxide mineral. No /sup 26/Mg excess was found in spite of the high /sup 27/Al//sup 24/Mg (1> or approx. =10/sup 3/) of some samples, indicating an initial (/sup 26/Al//sup 27/Al)/sub 0/<2 x 10/sup -7/, a factor of 250 less than found in some other Allende inclusions. The upper limit for Mg isotopic fractionation is 20% per amu. Anomalous but uniform Ca isotopic compositions were found for bulk samples of coexisting phases and microscopic grains. The Ca anomaly is a superposition of a large mass-dependent fractionation effect of 7.5% per amu favoring the heavy isotopes and small (1%--2%) ''nonlinear'' effects of presumably nuclear origin. If the lack of /sup 26/Al is due to a time delay of 6 x 10/sup 6/ yr for the formation of the hibonite inclusion, then condensation models require modification. The Ca effects suggest the alternative that /sup 26/Al was not uniformly distributed in the solar system. These results accentuate the curious and unexplained association between large mass fractionation and nuclear effects. They also reinforce the scenario which envisages an early solar system consisting of isotopically and chemically distinct reservoirs resulting from the incomplete mixing of several nucleosynthetic components. It is not evident whether these components originated within the solar system or from another star.
- Research Organization:
- Enrico Fermi Institute, University of Chicago
- OSTI ID:
- 6286397
- Journal Information:
- Astrophys. J., Lett.; (United States), Vol. 228:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
ALUMINIUM 26
ABUNDANCE
CALCIUM
METEORITES
CHEMICAL COMPOSITION
FRACTIONATION
ISOTOPE RATIO
MAGNESIUM
NUCLEOSYNTHESIS
SOLAR SYSTEM
ALKALINE EARTH METALS
ALUMINIUM ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
ELEMENTS
ISOTOPES
LIGHT NUCLEI
METALS
NUCLEI
ODD-ODD NUCLEI
RADIOISOTOPES
SECONDS LIVING RADIOISOTOPES
SEPARATION PROCESSES
YEARS LIVING RADIOISOTOPES
640101* - Astrophysics & Cosmology- Cosmic Radiation