Algorithms for neutron density and s-process nucleosynthesis in a low-mass asymptotic giant branch star

Algorithms for calculating neutron-capture nucleosynthesis in the context of low-mass AGB stars are presented. The primary neutron source is the (C-13)(alpha, n) O-16 reaction which is activated in the convective shell of an AGB star having the characteristics found in stellar model calculations. It is shown that a one-zone model is useful for obtaining estimates of the consequence of neutron-capture nucleosynthesis; for a typical pulse, this zone has a temperature of about 1.36 x 10 to the 8th K and a density of about 34,400 g/cu cm. This compares with a temperature of 1.50 x 10 to the 8th K and a density of 40,000 g/cu cm at the base of the convective shell. Each neutron release episode lasts for about 10 yr and, if C-13 is introduced into the convective shell at a constant rate, the mean neutron number density during most of this episode is shown by a given expression. 19 refs