The reasonable assumption of an approximately uniform nucleosynthesis rate yields an age for the Galaxy of 12.8 ± 3 Gyr, which again is consistent with current determinations from other methods.
) the ages of white dwarfs from cooling calculations (the age of the Galactic disk? This paper will focus on radioactive dating, an approach that has played a particularly important role historically.
Early abundance studies of metal poor stars [see, e.g., the reviews by Wheeler, Sneden, and Truran (12) and Mc William (13)] showed that abundances of nuclei normally attributable to the s-process were systematically depleted relative to r-process nuclei.
The recognition that the heavy element abundance patterns in extremely metal-deficient stars ([Fe/H] ≈ −3) involve exclusively r-process products (14) is now strongly supported by spectroscopic studies of an increasing number of such stars.
The uncertainties introduced by the subtraction of the s-process contribution to isolate the cosmoradiogenic component are significant.
Further complications are associated with the fact that the β decay rate of Re in stellar environments is sensitive to temperature.
The presence of naturally occurring radioactive nuclei in Galactic matter testifies to the fact that the age of the elements is finite.
To the extent that the long-lived nuclear species of interest are the products of nuclear transformations proceeding in stars and supernovae over the course of our own Galaxy’s history, they can be used to provide a measure of the duration of star formation activity and concomitant nucleosynthesis in the Galaxy.The production history of the ) the production ratios of the isotopes of uranium and thorium in the relevant (r-process) nucleosynthesis site.Abundance determinations for the thorium and uranium isotopes of interest are provided by analyses of meteoritic material.There are considerable uncertainties associated with the nuclear properties of the unstable, neutron-rich progenitors of the uranium and thorium isotopes of interest.Determinations of these production ratios available in the literature [see, e.g., the review articles of Cowan, Thielemann, and Truran (18, 19)] yield values that span a broad range: 1.40 ≤ ( The equations governing the time evolution of the abundance of a radioactive nuclear species are straightforward.Abundance clues to r-process history and the identification of the astrophysical site of r-process synthesis are reviewed in section 1.