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Reaction atlas · CNO cycles

Radiative capture · CNO-II

16O(p,γ)17F

: oxygen‑16 + proton → fluorine‑17 + gamma rayHow to read the notation

On this page

Oxygen-16 captures a proton and becomes radioactive fluorine-17. It is the slowest step of the second CNO cycle.

Because this capture is slow, most of the oxygen-16 in a star survives hydrogen burning. The small part that burns makes oxygen-17, whose amount relative to oxygen-16 is measured in red giants and in grains of stardust found in meteorites, and is used to test stellar models.

Facts

How well known
Known to about 4%: how the cross section changes with energy is well understood from theory, and the remaining uncertainty is in the overall scale of the measurements.
Reaction rates
Explore the rates →
Q-value · energy released
0.600 MeV
Gamow window
Product 17F
radioactive, t½ = 1.07 min
Kind
Radiative capture

How it was measured

2 measurements, 1997–2022Show the list
  1. 1997

    Direct measurement at the surface

    Cross sections for capture to the ground state and to the first excited state. The S-factor for the excited-state transition rises as the energy decreases, which the authors explained by the loose binding of the proton in the 1/2+ state. [1]

  2. 2022

    Calculation from theory · all reliable data sets, refitted

    All reliable cross sections fitted with a single-particle potential model, the ANCs of the 17F ground and first excited states used as scaling parameters, with statistical and systematic uncertainties treated separately; the rate uncertainty is ±4.2%, about half of the previously reported 7.5%. [2]

Measurements (EXFOR)

Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.

26 datasets in 11 EXFOR entries, 1954–2012 · 5 without an energy range, not drawn

core of a 15 M☉ star, T₉ = 0.035 (35 MK)

Lowest energy in EXFOR
132 keV
Hester et al., 1958 · σ · C0174.002
Distance from the Gamow peak
2.8 Gamow widths above
E₀ = 51.3 keV, window 36.9–65.7 keV
Rate from energies not in EXFOR
> 99.99%
at T₉ = 0.035, smooth estimate · > 99.99% of it lies below the lowest energy in EXFOR
10 keV100 keV1 MeV10 MeV100 MeVCentre-of-mass energy (keV)E₀ = 51.3 keVσSσ→Eₓdσ/dΩAyotherlowest in EXFOR 132 keV
  • 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
The datasets of the gap map, by quantity
QuantityDatasetsE_cm range (keV)
σcross section3132 keV – 580 keV
SS-factor3249 keV – 2.82 MeV
σ→Eₓpartial3470 keV – 2.4 MeV
dσ/dΩangular distribution9225 keV – 41.8 MeV
Aypolarization119.6 MeV – 19.6 MeV
…other2941 keV – 28.2 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.

Try it: an R-matrix evaluation

This system has a live AZURE2 model on this site: change the energies and widths of its levels and see how the fit to the data and the extrapolation to stellar energies change.

Details

How well known, in detail: A non-resonant direct-capture reaction whose energy dependence is fixed by theory; a Bayesian analysis (2022) gives the rate to ±4.2%, about half the earlier 7%, limited by the normalization of the surface data.

There are no resonances at stellar energies. The cross section is direct capture to the 17F ground state and to its first excited state, a weakly bound 1/2+ level whose extended wave function makes the capture to it dominant at low energy and gives the S-factor a steep rise towards zero energy. The energy dependence is therefore well described by direct-capture and microscopic models, and the rate rests on surface data scaled with such a model.

Solar Fusion II adopts S(0) = 10.6 ± 0.8 keV b from model calculations normalized to the data of 1973 and 1997. A 2008 evaluation, which corrected the data sets since 1958 for coincidence summing and stopping powers, gives the rate with an uncertainty of about 7%. A Bayesian fit of all reliable data, with a potential model whose scaling parameters are the asymptotic normalization coefficients of the two bound states, halves that uncertainty to ±4.2% (Iliadis et al. 2022).

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.

  • —E. G. Adelberger et al., Rev. Mod. Phys. 83, 195 (2011) [3]
  • —C. Iliadis et al., Phys. Rev. C 77, 045802 (2008) [4]
  • —B. Acharya et al., Rev. Mod. Phys. 97, 035002 (2025) [5]
  • —C. Iliadis et al., Phys. Rev. C 106, 055802 (2022) [2]

Open questions

  • Direct data closer to the Gamow window, to test the predicted rise of the S-factor at low energy.

Related reactions

References

  1. 1.

    R. Morlock, R. Kunz, A. Mayer, M. Jaeger et al.

    Halo properties of the first 1/2+ state in 17F from the 16O(p,γ)17F reaction

    Phys. Rev. Lett. 79, 3837 (1997) · 10.1103/PhysRevLett.79.3837

  2. 2.
  3. 3.

    E. G. Adelberger et al.

    Solar fusion cross sections II: the pp chain and CNO cycles

    Rev. Mod. Phys. 83, 195 (2011) · 10.1103/RevModPhys.83.195

  4. 4.

    C. Iliadis, C. Angulo, P. Descouvemont, M. Lugaro and P. Mohr

    New reaction rate for 16O(p,γ)17F and its influence on the oxygen isotopic ratios in massive AGB stars

    Phys. Rev. C 77, 045802 (2008) · 10.1103/PhysRevC.77.045802 · arXiv:0803.2757

  5. 5.

How to cite this page

J. Skowronski, 16O(p,γ)17F, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/16O-pg-17F.

Cite the date you used; it is the last change to this page.

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