Theoretical neutron-capture cross sections for r-process nucleosynthesis in the $^{48}$Ca region

Abstract

We calculate neutron capture cross sections for r-process nucleosynthesis in the 48 Ca region, namely for the isotopes 40−44 S, 46−50 Ar, 56−66 Ti, 62−68 Cr, and 72−76 Fe. 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.