Nucleosynthesis at the termination point of the s process

Abstract

Stellar cross sections of importance with respect to the termination of the s-process reaction chain have been determined for the two cases, 208Pb(n, γ)209Pb and 209Bi(n, γ)210Big, yielding kT=30 keV values of 〈σv〉/vT=0.31 ± 0.2 mb and 2.54±0.14 mb, respectively. The measurements were carried out by activation of Pb and Bi samples in a quasistellar neutron spectrum using gold as a cross section standard. With this technique the uncertainties reported in previous works could be considerably reduced. The measurements are complemented by a discussion of the recycling at the termination point of the s-process neutron capture chain in a 3M⊙ and [Fe/H]=-1.3 asymptotic giant branch star. At this metallicity, AGB stars give rise to the maximum production of s-process lead. The sensitivity of the isotopic lead abundances is discussed with respect to the remaining cross section uncertainties. The information obtained in this work is also of relevance for an assessment of the α activity due to a buildup of 210Po in Pb/Bi cooled fast reactor systems.