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Publication Date


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The Astrophysical Journal


The American Astronomical Society


New methods for using radioactive decays to date the time of nucleosynthesis in our Galaxy are preed in this work. The methods depend upon a comparison of the cosmoradiogenic abundances of ghter species with the abundances of their radioactive parents. The decays which can provide useful rmation of this type are Re187-Os187, and U238-Pb206. It will be shown that the amount of enrichment of the daughter products by radioactive decay throughout the history of our Galaxy is ulable. This calculation differs from previous radioactive chronologies which have concentrated on relative abundances of the radioactive species themselves, U2 U238, and Th232. Definitive numerical ulations at the present time are forestalled by uncertainties in several key measurable quantities, iculaily neutron-capture cross-sections an solar abundances. Tentative calculations based on probvalues of these quantities indicate that galactic nucleosynthesis began at least 5 X 1O years before formation of the solar system, and perhaps considerably earlier. Measurements capable of reducing uncertainty of these methods are emphasized.