RE-EVALUATION OF THE¹⁶O(N,γ)¹⁷O CROSS SECTION AT ASTROPHYSICAL ENERGIES AND ITS ROLE AS A NEUTRON POISON IN THEs-PROCESS

Abstract

The doubly-magic nucleus 16 O has a small neutron capture cross section of just a few tens of microbarn in the astrophysical energy region. Despite of this, 16 O plays an important role as neutron poison in the astrophysical slow neutron capture (s) process due to its high abundance. We present in this paper a re-evaluation of the available experimental data for 16 O(n, γ) 17 O and derive a new recommendation for the Maxwellian-averaged cross sections (MACS) between kT = 5−100 keV. Our new recommendations are lower up to kT = 60 keV compared to the previously recommended values but up to 14% higher at kT = 100 keV. We explore the impact of this different energy dependence on the weak s-process during core helium-(kT = 26 keV) and shell carbon burning (kT = 90 keV) in massive stars where 16 O is the most abundant isotope.

Direct capture cross section of Be9(n,γ)Be10

“…As usual, s-wave capture decreases with energy by roughly 1/ √ E, whereas p-wave capture increases with √ E. A transition from the 1/ √ E to the √ E behavior is found at several tens of keV. This is a typical result for light nuclei at the upper end of the p-shell like 12 C [21] and in the sd-shell (e.g., 16 O [22,23] and 26 Mg [9]). Important ingredients of the DC calculations like wave functions and overlaps are further illustrated in Fig.…”

Impact of the decay width in Breit-Wigner formula on Maxwellian-averaged cross section for neutron capture on 16O

“…16 O may be one of the candidates due to its high abundance and large reaction rate of neutron capture process. It has been shown that the difference of the 16 O(n, γ) 17 O rates apparently influence the weak s-process in massive stars [1], which trigger us to study the properties of 16 O(n, γ) 17 O, especially for its cross section.…”

Accelerator mass spectrometry measurement of the reaction Cl35(n,γ)Cl36 at keV energies

“…Lighter elements with high abundances and/or high neutron capture cross sections compete with the s-process nucleosynthesis of heavier elements by reducing the availability of neutrons. They can act either as "neutron absorbers," when the neutron is recycled in subsequent reaction steps [e.g., 16 O(n, γ ) 17 O(α, n) 20 Ne] or as "neutron poisons"' when the neutron is completely lost for the s-process nucleosynthesis [e.g., 14 N(n, p) 14 C or 25 Mg(n, γ ) 26 Mg] [3]. Hence, these neutron poisons reduce the efficiency of the s process.…”