The cross section of14N(n, p)14C at stellar energies and its role as a neutron poison forS-process nucleosynthesis

Abstract

The absolute average cross section (o-) of the 14N(n, p) 14C reaction has been measured using neutron spectra that closely resemble Maxwell-Boltzmann distributions with thermal energies of kT = 25.0 and 52.4 keV: (o-) = 0.81 ___ 0.05 and 0.52 4-0.06 mb, respectively. The resulting reaction rates are nearly the same at T9=0.29 and 0.61, and their average, NA (o-v) = (1.3 _+ 0.1) x 105 cm 3 s-1 mol-1, is about a factor of three smaller than the previously adopted values obtained by extrapolation between thermal and higher-energy data. Thus, the 14N(n, p) 14C reaction plays a correspondingly smaller role as a neutron poison for s-process nucleosynthesis.

AMS Applications in Nuclear Astrophysics: New Results for 13C(n,γ) 14C and 14N(n,p) 14C

“…The measurements by (Koehler & O'Brien 1989) support a 1/v energy dependence up to some 100 keV. Other experimental data in the energy range between 10 and 200 keV show good agreement, except for a measurement by Brehm et al (1988), which indicates cross-section values approximately a factor of two to three lower in this energy range (see Figure 2). This has a great impact on 14 N as a neutron poison, and also for its role on 19 F production, since the protons produced through 14 N(n,p) 14 C play an important role in synthesizing this nuclide.…”

“…Much more work exists for 14 N(n,p) 14 C in the keV energy range (Koehler & O'Brien 1989, Brehm et al 1988, Kii et al 1999, Sanami et al 1997. Experimental data are available for energies up to 7 MeV and there exists one additional data-point at 14.5 MeV.…”

Accelerator mass spectrometry measurements of theC13(n,γ)C14andWallner1, Bichler2, Buczak3 et al. 2016Phys. Rev. CSelf Cite281170View full textAdd to dashboardCite

“…After each thermal instability the convective envelope can sink deep into the He-rich intershell, dredging up to the stellar surface the products of He burning (such as 12 C) and of the s process. During the subsequent long phases of H burning the larger part of the neutron exposure is produced via 13 C(α,n) reactions in the so-called " 13 C pocket" when a certain amount of H may mix from the envelope into the He intershell at the deepest extent of each dredge-up episode. The 13 C pocket consists of a thin layer as shown in Fig.…”

“…During the subsequent long phases of H burning the larger part of the neutron exposure is produced via 13 C(α,n) reactions in the so-called " 13 C pocket" when a certain amount of H may mix from the envelope into the He intershell at the deepest extent of each dredge-up episode. The 13 C pocket consists of a thin layer as shown in Fig. 1 that forms after an He shell flash, when a certain amount of H is mixed from the envelope into the He intershell.…”

“…1 that forms after an He shell flash, when a certain amount of H is mixed from the envelope into the He intershell. These protons are captured by the 12 C admixture in the intershell leading to the reaction sequence 12 C(p,γ ) 13 N(β + ) 13 C. The exact way the 13 C pocket is formed is complicated and still affected by persistent uncertainties as summarized in [1]. For practical reasons, a parametrized form was initiated by Gallino et al [3] that was essentially guided by the observed s abundances.…”