The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars.
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| Title: | The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars. |
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| Authors: | Dauphas, Nicolas |
| Source: | Nature. 6/30/2005, Vol. 435 Issue 7046, p1203-1205. 3p. |
| Subjects: | Milky Way, Galaxies, Galactic halos, Meteorites, Stellar evolution, Heavy elements, Chemical elements, Astrophysics |
| Abstract: | Some heavy elements (with atomic number A > 69) are produced by the ‘rapid’ (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from ∼0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely . This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way ( in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution. [ABSTRACT FROM AUTHOR] |
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| Database: | Psychology and Behavioral Sciences Collection |
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