Isotopic analysis of early solar system objects by an ion microprobe: parametric studies and initial results

Goswami, J. N. ; Srinivasan, G. (1994) Isotopic analysis of early solar system objects by an ion microprobe: parametric studies and initial results Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences, 103 (1). pp. 57-82. ISSN 0253-4126

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Magnesium, potassium and calcium isotope compositions in terrestrial samples and refractory phases from primitive meteorites are determined using an ion microprobe. A thorough investigation of the different instrument parameters is carried out to ensure that conditions necessary for high mass resolution and high precision isotopic studies are adequately satisfied. The instrument can be tuned to achieve mass resolution (M/ΔM) of up to 10,000 (M≤60); it has a very good dynamic stability (ΔB/B#8804;10 ppm over durations of #8804;40 minutes) and the counting system has an effective dead-time of #8804;25 nsec and a dynamic background of #8804;0.01 c/s. Reproducibility and precision of isotopic measurements are checked by analyzing magnesium and titanium isotopic compositions in terrestrial standards and isotopically doped silicate glasses. A precision of 2% (2σ m ) was achieved during magnesium isotopic analysis in samples with low Mg content (200 ppm). Results from studies of magnesium and potassium isotopic compositions in several Ca-Al-rich refractory inclusions (CAIs) from the primitive meteorites Efremovka and Grosnaja, representing some of the early solar system objects, are presented. The well-behaved Mg-Al isotopic systematics confirm the pristine nature of the Efremovka CAIs inferred earlier from petrographic and trace element studies. The Grosnaja CAIs that have experienced secondary alterations show disturbed magnesium isotopic systematics. Observation of excess 26Mg in several of the analyzed CAIs confirms the presence of the now extinct 26Al (t ½ =7×105 years) in the solar nebula at the time of CAI formation. Our data also suggest a relatively uniform distribution of 26Al in the solar nebula. Several Efremovka CAIs with excess 26Mg also have excess 41K resulting from the decay of 41Ca (t ½105 years). This observation constrains the time interval between cessation of nucleosynthetic input to the solar nebula and the formation of some of the first solar system solids (CAIs) to less than a million years.

Item Type:Article
Source:Copyright of this article belongs to Indian Academy of Sciences.
Keywords:Ion Microprobe; Isotopes; Extinct Nuclides; Meteorites; Solar System; Solar Nebula
ID Code:14652
Deposited On:12 Nov 2010 13:53
Last Modified:16 May 2016 23:37

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