Exploration of direct neutron capture with covariant density functional theory inputs

Predictions of direct neutron capture are of vital importance for simulations of nucleosynthesis in supernovae, merging neutron stars, and other astrophysical environments. We calculated direct capture cross sections using nuclear structure information obtained from a covariant density functional theory as input for the fresco coupled reaction channels code. We investigated the impact of pairing, spectroscopic factors, and optical potentials on our results to determine a robust method to calculate cross sections of direct neutron capture on exotic nuclei. Our predictions agree reasonably well with experimental cross section data for the closed shell nuclei ${}^{16}\mathrm{O}$ and ${}^{48}\mathrm{Ca},$ and for the exotic nucleus ${}^{36}\mathrm{S}$. We then used this approach to calculate the direct neutron capture cross section on the doubly magic unstable nucleus ${}^{132}\mathrm{Sn}$ which is of interest for the astrophysical r-process.

Figure 1

Direct neutron capture cross section ${\sigma }_{\mathrm{DC}}$ for ${}^{16}\mathrm{O}(n,\gamma ){}^{17}\mathrm{O}$. Full squares: experimentally measured cross section [33]. Pink line: fresco calculations with s.p. level energies from RAB approach. Green line: similarly but with RMF s.p. level energy inputs. Black line: similar with experimental level energies. KD optical potentials of scattering states are used with SF = 1.

Figure 2

Similar as Fig. 1, but for the ${}^{36}\mathrm{S}(n,\gamma ){}^{37}\mathrm{S}$ reaction. Solid lines refer to the results of the fresco code with SF = 1, dashed lines use SF from $\left(d,p\right)$ measurements [40]).

Figure 3

Similar as Fig. 2, but for the ${}^{48}\mathrm{Ca}{(n,\gamma )}^{49}\mathrm{Ca}$ reaction. Blue lines refer to the results with CH89 optical potentials.

Figure 4

Calculations of direct capture cross sections for ${}^{132}\mathrm{Sn}(n,\gamma ){}^{133}\mathrm{Sn}$ and the individual level contributions. Solid lines: fresco calculations with measured s.p. level energy inputs with KD optical potential and SF = 1. Dashed lines: ${\sigma }_{\mathrm{DC}}$ from Ref. [48].

Figure 5

Calculations of direct capture cross sections for ${}^{132}\mathrm{Sn}(n,\gamma ){}^{133}\mathrm{Sn}$ by different approaches with SF = 1. Black solid line: fresco calculations with measured s.p. level energy inputs with KD optical potential. Black dashed line: fresco calculations with measured s.p. level energy inputs with CH89 optical potential. Pink line: fresco calculations with RAB s.p. level energy inputs with KD optical potential. Blue line: fresco calculations with RAB s.p. level energy inputs with CH89 optical potential. Green line: ${\sigma }_{\mathrm{DC}}$ from Ref. [48].