The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

Details The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005natur.435.1203d&link_type=abstract

Nature, Volume 435, Issue 7046, pp. 1203-1205 (2005).

Physics

12

Scientific paper

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.

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