Theoretical neutron-capture cross sections for r-process nucleosynthesis in the 48Ca region
Abstract
We calculate neutron capture cross sections for r-process nucleosynthesis in the 48Ca region, namely for the isotopes 40-44S, 46-50Ar, 56-66Ti, 62-68Cr, and 72-76Fe. While previously only cross sections resulting from the compound nucleus reaction mechanism (Hauser-Feshbach) have been considered, we recalculate not only that contribution to the cross section but also include direct capture on even-even nuclei. The level schemes, which are of utmost importance in the direct capture calculations, are taken from quasi-particle states obtained with a folded-Yukawa potential and Lipkin-Nogami pairing. Most recent deformation values derived from experimental data on β-decay half lives are used where available. Due to the consideration of direct capture, the capture rates are enhanced and the "turning points" in the r-process path are shifted to slightly higher mass numbers. We also discuss the sensitivity of the direct capture cross sections on the assumed deformation.