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Contamination of the Th II line and the age of the Galaxy

Lawler, J. E. and Whaling, W. and Grevesse, N. (1990) Contamination of the Th II line and the age of the Galaxy. Nature, 346 (6285). pp. 635-637. ISSN 0028-0836. doi:10.1038/346635a0.

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The age of the Galaxy may be estimated from observations of the ratio of stellar abundances of thorium, which has only one long-lived isotope with a half-life comparable to the suspected age of the Galaxy, and neodymium, a stable element. The Th/Nd abundance ratio in a sample of G-dwarf stars of different ages was derived by Butcher from the intensities of one Th II and one Nd II absorption line, and indicated a rather young galactic age of 9.6 Gyr. But the Th II line is blended with a Co I line. Here we determine the transition probability of the Co I line by combining radiative lifetime and branching-ratio measurements. We show that the Co I contribution cannot be neglected in deriving Th/Nd ratios. By comparing our results with predictions based on models of galactic chemical evolution, we suggest a revised age of the Galaxy of 15–20 Gyr.

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Additional Information:© 1990 Nature Publishing Group. Received 12 February; accepted 27 June 1990. We thank W. Nijs for help with the calculations and M. Arnould, K. Takahashi, P. Magain, A. Noels, E. Anders and H. R. Butcher for discussions and suggestions. This research was supported in part by the NSF.
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Issue or Number:6285
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56591
Deposited By: Tony Diaz
Deposited On:13 Apr 2015 17:10
Last Modified:10 Nov 2021 21:01

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