Abstract
Neutron captures are likely to occur in the crust of accreting neutron stars (NSs). Their rate depends on the thermodynamic state of neutrons in the crust. At high densities, neutrons are degenerate. We find degeneracy corrections to neutron capture rates off nuclei, using cross sections evaluated with the reaction code TALYS. We numerically integrate the relevant cross sections over the statistical distribution functions of neutrons at thermodynamic conditions present in the NS crust. We compare our results to analytical calculations of these corrections based on a power-law behavior of the cross section. We find that although an analytical integration can simplify the calculation and incorporation of the results for nucleosynthesis networks, there are uncertainties caused by departures of the cross section from the power-law approach at energies close to the neutron chemical potential. These deviations produce non-negligible corrections that can be important in the NS crust.
Highlights
X-ray burst and superburst observations are attributed to accreting neutron stars (NSs)(see, e.g., [1,2])
We study the behavior of R for 39 Mg, 46 Mg, and 58 Ni using three different cross sections: (1) the results obtained directly with TALYS, (2) the power-law indexes and energy ranges as provided in Reference [6] (for the 39 Mg(n, γ)40 Mg and 46 Mg(n, γ)47 Mg reactions), and (3) our power-law fit to TALYS cross sections
Ni was selected to allow reproducible results, as it is a common result of rp-process nucleosynthesis
Summary
X-ray burst and superburst observations are attributed to accreting neutron stars (NSs). The energy released during the reactions heats up the star material, triggering the bursts and contributing to the synthesis of proton-rich nuclei via rp-process nucleosynthesis. Besides the important effect of neutron degeneracy, a reliable calculation of capture rates strongly depends on the relevant cross sections. Universe 2019, 5, 36 power-law behavior of such cross sections that should be valid up to some neutron energy and thermodynamic conditions With such behavior, the authors found an analytical correction to the neutron capture rates. An analytical correction allows for an easy implementation in nucleosynthesis calculations In this contribution, we study the feasibility and validity of a power-law approximation by numerically integrating the absorption cross sections over the Fermi–Dirac distribution of the neutrons. Have showed that there will be a correction to capture rates as a result of the electron plasma, and we will study this effect in later work
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