Nitrogen-14 absorbs a neutron and releases a proton, becoming carbon-14. It is the most dangerous neutron poison in the 13C pocket of giant stars.
In an AGB star the neutrons that build the heavy elements come from a thin layer rich in carbon-13, the 13C pocket. Wherever that layer also holds nitrogen-14, the nitrogen captures neutrons readily and turns them into protons, so they never reach the iron seeds. How large this loss is decides how many neutrons each iron nucleus receives, and so how far the s-process climbs towards lead. The reaction is also used in medicine and dosimetry, which is one reason it has been measured often.
Facts
- How well known
- Well measured at low energies; at the energies inside stars, recent experiments are correcting older values.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 0.626 MeV
- Thermal energy kT
- about 8 keV, the energy of a gas at 90 million kelvin
- Why no Gamow window
- A neutron feels no Coulomb barrier, so there is no Gamow window: the relevant energies are those of the thermal distribution itself, around kT.
- Product 14C
- radioactive, t½ = 5 700 yr
- Kind
- Particle-exchange reaction
How it was measured
3 measurements, 2016–2025Show the listHide the list
2016
Karlsruhe Van de GraaffKernforschungszentrum Karlsruhe (now Karlsruhe Institute of Technology)
Activation · quasi-Maxwellian kT = 25 keV; 123–182 keV
Irradiations at Karlsruhe, 14C counted by AMS at VERA (Vienna); about two times lower cross sections between 100 and 200 keV than previous experiments and evaluations. [1]
2023
n_TOF, CERNCERN
Neutron beams and time of flight · subthermal to 800 keV (neutron energy)
EAR2 measurement relative to 10B(n,α)7Li and 235U(n,f); thermal cross section 1.809 ± 0.045 b, consistent with ENDF/B-VIII.0 and JEFF-3.3; first two resonances resolved; MACS derived. [2]
2025
HZDR Tandetron, Dresden-RossendorfHelmholtz-Zentrum Dresden-Rossendorf
Neutron beams and time of flight · 0.1–12 MeV (neutron energy), total cross section
Transmission measurement at the nELBE time-of-flight facility, only the second high-sensitivity total cross section of 14N + n, as a constraint for R-matrix evaluations of the (n,p) channel. Good agreement with earlier data except at the lowest resonance, E_n = 433 keV. [3]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
59 datasets in 33 EXFOR entries, 1939–2024 · 14 without an energy range, not drawn
AGB ¹³C pocket, kT = 7.76 keV
- Lowest energy in EXFOR
- 8.37 meV
- KOEHLER et al., 1989; Koehler, 1993; Wagemans et al., 2000; Kitahara et al., 2019; Torres-Sanchez et al., 2023 · σ · 13164.002
- Maxwellian averages measured
- 6 sets
- kT from 25.3 meV to 100 keV
- Rate from energies not in EXFOR
- < 0.01%
- at kT = 7.76 keV, smooth estimate
- Energies that matter at kT = 7.76 keV
- Outlined bars are shown but not counted (the rule is under “How these numbers are made”).
- A diamond is a dataset at a single energy. Bars running off the right edge continue to higher energies.
The datasets of the gap map, by quantity
| Quantity | Datasets | E_cm range (keV) |
|---|---|---|
| σcross section | 28 | 8.37 meV – 56.5 MeV |
| σ→Eₓpartial | 1 | 4.67 MeV – 12.2 MeV |
| dσ/dΩangular distribution | 5 | 460 keV – 55 MeV |
| ωγresonance strength | 2 | 460 eV – 601 eV |
| MACSMaxwellian average | 6 | 25.3 meV – 100 keV |
| …other | 3 | 1.63 meV – 6.57 meV |
How these numbers are made
Lowest measured energy, everywhere in the data explorer: the lowest centre-of-mass energy at which a dataset in EXFOR measures the reaction itself (cross section, S-factor, angular distribution, yield or resonance strength), judged point by point. A point counts when it is a value, not an upper or lower limit, when it lies at least one standard deviation above zero, and when its energy is physical: at least 1 keV for charged particles, and not below the threshold of an endothermic reaction. Not counted: extrapolated, calculated, evaluated or derived values; superseded, deleted or preliminary data; ratios; a single S-factor value, which in EXFOR is a fit result; and indirect methods (Trojan horse, Coulomb dissociation, ANC, surrogate reactions), recognized from EXFOR's method and analysis codes, their text and the title. Frame and unit errors of EXFOR are corrected first, and values the literature shows to be upper limits are read as limits, from a list that gives the evidence for each. Datasets that reach the same energy within 0.5% are all credited, earliest first. Rate from energies not in EXFOR: the share of the rate integrand at that temperature outside the energy ranges the counted datasets cover (from their lowest measured point to their highest), with a constant S-factor (σ ∝ S(E₀)/E · e^−2πη, so the integrand is e^(−E/kT − 2πη)); for a neutron capture, σ ∝ 1/v. Resonances make the real integrand lumpy, so read it as a smooth baseline.
Details
How well known, in detail: Recent activation and time-of-flight data disagree with older ones in the keV region; the n_TOF data cover the whole range from thermal to 800 keV with 2.5% accuracy.
The first resonances of 14N(n,p)14C lie at 492.7 and 644 keV. Its competition with 13C(α,n)16O for the neutrons of the pocket is why stellar models require the 13C pocket to form where little 14N is present (Straniero et al. 2006). Activation at Karlsruhe with a quasi-Maxwellian spectrum of kT = 25 keV and at 123–182 keV, with the 14C counted by accelerator mass spectrometry at VERA, gave cross sections about two times lower between 100 and 200 keV than earlier experiments and evaluations (Wallner et al. 2016). A time-of-flight measurement at n_TOF EAR2 from subthermal energy to 800 keV, relative to 10B(n,α) and 235U(n,f), gave a thermal cross section of 1.809 ± 0.045 b and a 492.7 keV resonance whose low-energy tail lies below the evaluations, and Maxwellian-averaged cross sections from it (Torres-Sánchez et al. 2023).
The protons it releases are not simply lost. Captured by 12C they make 13C again, through 12C(p,γ)13N(β+)13C, and so a little of the neutron source; captured by 18O they open the chain 18O(p,α)15N(α,γ)19F, by which AGB stars make fluorine.
Evaluations
Compilations that combine the data into a recommended rate.
Open questions
- The cross section between about 10 and 100 keV, where the measurements of different groups still differ.
Related reactions
References
- 1.
A. Wallner et al.
Accelerator mass spectrometry measurements of the 13C(n,γ)14C and 14N(n,p)14C cross sections
Phys. Rev. C 93, 045803 (2016) · 10.1103/PhysRevC.93.045803
- 2.
P. Torres-Sánchez et al. (n_TOF Collaboration)
Phys. Rev. C 107, 064617 (2023) · 10.1103/PhysRevC.107.064617 · arXiv:2212.05128
- 3.
R. J. deBoer et al.
Total cross section of 14N + n from 0.1 to 12 MeV
Phys. Rev. C 112, 025805 (2025) · 10.1103/frgb-j5c3 · arXiv:2505.04995
- 4.
Z. Y. Bao, H. Beer, F. Käppeler, F. Voss, K. Wisshak, T. Rauscher
Neutron cross sections for nucleosynthesis studies
At. Data Nucl. Data Tables 76, 70 (2000) · 10.1006/adnd.2000.0838
- 5.
I. Dillmann, T. Szücs, R. Plag, Z. Fülöp, F. Käppeler, A. Mengoni, T. Rauscher
The Karlsruhe Astrophysical Database of Nucleosynthesis in Stars project – status and prospects
Nucl. Data Sheets 120, 171 (2014) · arXiv:1408.3688
- 6.
I. Dillmann et al.
Proc. Int. Conf. on Nuclear Data for Science and Technology 2007 (EDP Sciences, 2008), p. 575 (2008) · 10.1051/ndata:07303 · arXiv:0806.2076
How to cite this page
J. Skowronski, 14N(n,p)14C, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/14N-np-14C.
Cite the date you used; it is the last change to this page.
Something wrong or missing? Report an error (opens a new issue on GitHub) · Suggest a reaction (opens a new issue on GitHub)