Fluorine-19 captures a proton and keeps it, becoming neon-20. This is the way out of the CNO cycles towards heavier elements.
In all the CNO cycles the catalyst nuclei carbon, nitrogen, oxygen and fluorine are recycled, so their total number stays the same. This reaction is the exception: it carries material out of the cycles into neon, from which the NeNa and MgAl cycles can build heavier nuclei. Its rate, compared with the much more frequent 19F(p,α)16O, sets how fast this leakage happens in very hot hydrogen burning, as in massive stars without heavy elements and in nova explosions.
Facts
- How well known
- Measured underground down to fairly low energies. Below them the rate depends on weak resonances not yet seen directly, and on how often this reaction wins over its competitor 19F(p,α)16O.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 12.843 MeV
- Kind
- Radiative capture
On the timeline
How it was measured
2 measurements, 2008–2022Show the listHide the list
2008
Nuclear Science Laboratory, Notre DameUniversity of Notre Dame
Direct measurement at the surface · 200–760 keV
Resonances at 323.9, 564 and 634 keV and interference terms between them; only an upper limit for the expected resonance at 213 keV. Only the transition to the first excited state of 20Ne was measured. [1]
2022
JUNAChina Jinping Underground Laboratory
Direct measurement underground · down to 186 keV
Direct measurement at the China JinPing Underground Laboratory; a key resonance at 225 keV raises the rate near 0.1 GK by up to a factor of 7.4. Stellar models then give a stronger breakout from the CNO cycle in first stars, a possible source of the calcium seen in the most iron-poor stars. [2]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
19 datasets in 8 EXFOR entries, 1948–2021 · 1 without an energy range, not drawn
- Lowest energy in EXFOR
- 277 keV
- Subotic et al., 1979 · dσ/dΩ · F0795.002 Not yet in EXFOR: JUNA (2022), down to 186 keV.
- Distance from the Gamow peak
- 5.1 Gamow widths above
- E₀ = 70.6 keV, window 50.5–90.7 keV
- Rate from energies not in EXFOR
- > 99.99%
- at T₉ = 0.05, smooth estimate · > 99.99% of it lies below the lowest energy in EXFOR
- Gamow window, hatched where no measurement reaches
- 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 | 1 | 317 keV – 1.29 MeV |
| σ→Eₓpartial | 3 | 3.29 MeV – 24.1 MeV |
| dσ/dΩangular distribution | 8 | 277 keV – 12.6 MeV |
| Aypolarization | 2 | 3.24 MeV – 12.6 MeV |
| ωγresonance strength | 3 | 323 keV – 888 keV |
| …other | 1 | 3.89 MeV – 12.2 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: Underground data now reach 186 keV; below that the rate depends on weak resonances not yet measured directly, and on the (p,γ)/(p,α) ratio.
The γ-ray channel is weak compared with the α channels of the same 20Ne states, so measurements at low energy need intense beams and low-background detection, which motivated underground experiments. The rate at the relevant temperatures depends on low-energy resonances and on the non-resonant contribution, and on the γ-ray branchings of the 20Ne states near the proton threshold. A surface measurement in 2008 observed only the transition to the first excited state of 20Ne and gave an upper limit for the resonance near 213 keV.
The JUNA experiment, deep under the JinPing mountain, reached E = 186 keV and identified a key resonance at 225 keV; near 0.1 GK its rate is up to 7.4 times the previous recommendation. Before the JUNA result, an R-matrix analysis fitted the (p,γ), (p,α) and (p,p) data together (deBoer et al. 2021). It found the rate uncertainty considerably larger than previously reported.
The causes are unresolved interferences, possible threshold and subthreshold states and direct capture. A Gamow shell model calculation gives, near 0.1 GK, a rate close to the JUNA one (Dong et al. 2024, preprint). A 19F + p measurement is under way at the LUNA 400 kV accelerator.
Peak energy E0 ± half the 1/e width, centre of mass, from the AME2020 masses.
Evaluations
Compilations that combine the data into a recommended rate.
- —B. Acharya et al., Rev. Mod. Phys. 97, 035002 (2025) [3]
Open questions
- The strength of the lowest-energy resonances and the non-resonant contribution.
- The leakage ratio (p,γ)/(p,α) at the temperatures of hot hydrogen burning.
Discussed on the open-questions page
Related reactions
References
- 1.
A. Couture, M. Wiescher et al.
Measurement of the 19F(p,γ)20Ne reaction and interference terms from E(c.m.) = 200–760 keV
Phys. Rev. C 77, 015802 (2008) · 10.1103/PhysRevC.77.015802
- 2.
L. Zhang et al. (JUNA Collaboration)
Measurement of 19F(p,γ)20Ne reaction suggests CNO breakout in first stars
Nature 610, 656 (2022) · 10.1038/s41586-022-05230-x · arXiv:2302.09802
- 3.
B. Acharya et al.
Solar fusion III: New data and theory for hydrogen-burning stars
Rev. Mod. Phys. 97, 035002 (2025) · 10.1103/8lm7-gs18 · arXiv:2405.06470
- 4.
R. J. deBoer et al.
The 19F(p,γ)20Ne and 19F(p,α)16O reaction rates and their effect on calcium production in Population III stars
Phys. Rev. C 103, 055815 (2021)
- 5.
G. X. Dong, X. B. Wang, N. Michel, M. Płoszajczak
19F(p,γ)20Ne reaction rate and the puzzling calcium abundance in metal poor stars
arXiv preprint (2024) · arXiv:2411.17243
How to cite this page
J. Skowronski, 19F(p,γ)20Ne, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/19F-pg-20Ne.
Cite the date you used; it is the last change to this page.
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