Nuclear Chronologies for the Galaxy

The ratios U²³⁵/U²³⁸, Th²³²/U²³⁸, Pu²⁴⁴/U²³⁸, and I¹²⁹/I¹²⁷ have been used to obtain self-consistent solutions for the time evolution of r-process nuclei. Using Pu²⁴⁴/U²³⁸ = 1/30, the solutions all have a large amount of initial production, with a duration of from 0 to 10¹⁰ years, followed by a relatively quiescent period (~3 X 10⁹ years) terminated by a nucleosynthetic event that possibly initiated the separation of the solar system. For values of Pu²⁴⁴ less than 1/60 models of uniform synthesis terminated by a sharp nucleosynthetic event are possible.