The Isotopic Composition of Mg and the Implied Limits on ²⁶Al in the Early Solar System. Nucleosynthesis of ²⁶Al. And Nucleosynthetic Chronologies for the Galaxy

Citation

Schramm, David Norman (1971) The Isotopic Composition of Mg and the Implied Limits on ²⁶Al in the Early Solar System. Nucleosynthesis of ²⁶Al. And Nucleosynthetic Chronologies for the Galaxy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/J2VA-1S31. https://resolver.caltech.edu/CaltechTHESIS:06082018-102752217

Abstract

A particular isotope pair of astrophysical interest, ²⁶Al-²⁶Mg, was investigated in detail. A high precision mass spectrometric technique was developed whereby Mg isotopic compositions could be analyzed to better than five parts in 10⁴.

Feldspar (high Al, low Mg) mineral separates were carried out on several meteoritic and lunar samples. No anomalous ²⁶Mg values were found. Thus, there is no evidence for the existence of ²⁶ Al at the formation of the solar system.

Upper limits on the possible amount of ²⁶Al at solidification in the extraterrestrial samples were calculated. These limits were used to estimate the maximum change in central temperature of a planetary object which could be produced by the ²⁶Al decay.

A review is given of the production mechanisms for ²⁶Al and it has been shown that a flux of at least 4 x 10¹⁸ protons/cm² is required to produce enough ²⁶ Al to melt the cores of planetary objects.

The general problem of nucleosynthetic chronologies has been investigated. Nucleochronologies for the galaxy have been calculated using²³⁵U;²³⁸U,²³²Th/²³⁸U, ²⁴⁴Pu/²³⁸U (or preferably ²⁴⁴Pu/²³²Th),and ¹²⁹I/¹²⁷I. The systematics of the nucleochronologic equations are derived and it has been found that the mean age of the elements can be found from long-lived radioactive nucleii in a manner which is independent of the time dependent production rate. It has also been found that the interval between the termination of nucleosysthesis and the time of formation of solid bodies in the solar system can be determined model independently from the short~lived nucleii. In addition, some information on the time dependent shape of the production function can also be determined model independently.

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