Stellar (n, γ) cross sections for Br and Rb: Matching the weak and mains-process components

Abstract

The stellar ($n, \ensuremath{\gamma}$) cross sections of $^{79}\mathrm{Br}$, $^{81}\mathrm{Br}$, $^{85}\mathrm{Rb}$, and $^{87}\mathrm{Rb}$ have been determined by a series of ten activation measurements in a quasistellar neutron spectrum corresponding to a thermal energy of $\mathit{kT} = 25$ keV. The final uncertainties between 3 and 10% were dominated by the \ensuremath{\gamma}-ray intensities in the decay of the respective reaction products. All other uncertainties were significantly reduced through variation of the experimental parameters. The consequences of these results for $s$-process nucleosynthesis of Br and Rb, and in particular of the local $s$-only isotopes $^{80, 82}\mathrm{Kr}$ and $^{86, 87}\mathrm{Sr}$, are discussed with respect to the branching points at $^{79}\mathrm{Se}$ and $^{85}\mathrm{Kr}$. The contributions of both the main $s$ component from thermally pulsing low mass asymptotic giant branch stars and the weak $s$ component from massive stars are considered in this analysis.