¹⁷O(p,γ)¹⁸F · Reaction atlas

Oxygen-17 captures a proton and becomes radioactive fluorine-18. It opens the third CNO cycle.

In nova explosions this reaction makes fluorine-18. When fluorine-18 decays it emits positrons, and their annihilation produces γ-rays that space telescopes could detect in the first hours after the explosion. The rate also sets, together with ¹⁷O(p,α)¹⁴N, how much oxygen-17 and oxygen-18 a nova ejects, which is compared with the isotope ratios of presolar grains thought to come from novae.

Facts

How well known: Well measured at the temperatures of nova explosions; at the lower temperatures of ordinary stars it depends on a very weak resonance measured directly only once.
Live evaluation: No live evaluation yet · Evaluations
Reaction rates: Explore the rates →
Q-value · energy released: 5.607 MeV
Gamow window: 65 ± 19 keVAGB star, 50 MK (CNO-III)
165 ± 61 keVclassical nova, 0.2 GK (CNO-III)
Product ¹⁸F: radioactive, t_½ = 1.83 h
Kind: Radiative capture

How it was measured

8 measurements, 2005–2024, 3 at LUNAShow the list

2005
LENA, TUNLTriangle Universities Nuclear Laboratory
Direct measurement at the surface · 140–540 keV (proton energy)
Proton beams of up to 100 µA on tantalum backings anodised in ¹⁷O-enriched water; new thermonuclear rate including the 183 keV resonance. [1]
2005
CSNSM, OrsayCentre de Sciences Nucléaires et de Sciences de la Matière (CNRS/IN2P3 and Université Paris-Sud), since 2020 part of IJCLab
Activation · around Ep = 194 keV
The (p,γ) channel of the 183 keV resonance measured by ¹⁸F activation, together with the (p,α) channel. [2]
2012
DRAGON, TRIUMFTRIUMF
Inverse kinematics and recoil separators · 250–500 keV
S-factor measured in inverse kinematics with the DRAGON recoil separator, which detects the ¹⁸F recoils directly. [3]
2012
Nuclear Science Laboratory, Notre DameUniversity of Notre Dame
Direct measurement at the surface
The primary γ-ray transitions were used in an R-matrix analysis to estimate the direct-capture contribution; the new rate combines these data with earlier S-factor determinations. [4]
2012
LUNA 400 kVLaboratori Nazionali del Gran Sasso (INFN)
Direct measurement underground · 200–370 keV
First direct measurement in the Gamow window of classical novae; ωγ(183 keV) = 1.67 ± 0.12 µeV, the most precise value then, and a rate uncertainty reduced by a factor of 4. [5]
2014
LUNA 400 kVLaboratori Nazionali del Gran Sasso (INFN)
Direct measurement underground · nova Gamow window
Full analysis of the LUNA campaign with prompt γ-ray detection and activation; recommended rate with which the oxygen and fluorine isotopes ejected by novae are predicted to about 10%. [6]
2015
LENA, TUNLTriangle Universities Nuclear Laboratory
Direct measurement at the surface · 170–530 keV (proton energy)
Beam currents up to 2 mA; ωγ = (1.86 ± 0.13) µeV for the resonance at Ep = 193 keV and (13.70 ± 0.96) meV at 518 keV, and a direct-capture S(0) = 4.82 ± 0.41 keV b. [7]
2024
LUNA 400 kVLaboratori Nazionali del Gran Sasso (INFN)
Direct measurement underground · 64.5 keV resonance
First direct measurement of the 64.5 keV resonance, the lowest strength ever measured directly: ωγ = 30 ± 6 (stat) ± 2 (syst) peV. The proton width, 34 ± 7 ± 3 neV, agrees with the LUNA result from the (p,α) channel. [8]

Measurements (EXFOR)

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

33 datasets in 11 EXFOR entries, 1973–2017 · 4 without an energy range, not drawn

Temperature

AGB star, T₉ = 0.05 (50 MK)classical nova, T₉ = 0.2 (200 MK)

Lowest energy in EXFOR: 160 keV; Buckner et al., 2015 · S · C2155.002 Not yet in EXFOR: LUNA 400 kV (2024), 64.5 keV resonance.
Distance from the Gamow peak: 2.5 Gamow widths above; E₀ = 65.1 keV, window 45.8–84.5 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

The datasets of the gap map, by quantity
Quantity	Datasets	E_cm range (keV)
σcross section	3	257 keV – 1.7 MeV
SS-factor	7	10 keV – 1.78 MeV
σ→Eₓpartial	5	167 keV – 1.53 MeV
dσ/dΩangular distribution	6	283 keV – 1.81 MeV
ωγresonance strength	8	557 eV – 1.04 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.

All measurements (33)Compound nucleus ¹⁸F

Details

How well known, in detail: The nova-relevant resonance is measured directly to about 7%; at lower temperatures the 64.5 keV resonance, measured directly only once, and the direct-capture component dominate the uncertainty.

At nova temperatures the rate is dominated by the resonance at E = 183 keV together with the non-resonant direct-capture contribution; at lower temperatures the narrow resonance at 64.5 keV also contributes. The 183 keV resonance strength and the direct-capture S-factor have been measured with prompt-γ, activation and recoil-separator techniques; the γ-ray decay of the resonance proceeds through many cascades, which makes efficiency and angular corrections important. The LUNA measurements at Gran Sasso gave ωγ(183 keV) = 1.67 ± 0.12 µeV and reduced the rate uncertainty at nova temperatures by a factor of 4; the lower background revealed γ-ray transitions missed at the surface. In 2024 LUNA also measured the 64.5 keV resonance directly, ωγ = 30 ± 6 (stat) ± 2 (syst) peV, about twice the value adopted from indirect data.

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) [9]

Open questions

The direct-capture S-factor between the low-energy resonances.
The strength of the 64.5 keV resonance, where the direct result is about twice the value from indirect data.

Related reactions

References

1.
C. Fox, C. Iliadis, A. E. Champagne, R. P. Fitzgerald, R. Longland, J. Newton, J. Pollanen and R. Runkle
Thermonuclear reaction rate of ¹⁷O(p,γ)¹⁸F
Phys. Rev. C 71, 055801 (2005) · 10.1103/PhysRevC.71.055801
2.
A. Chafa, V. Tatischeff et al.
Hydrogen burning of ¹⁷O in classical novae
Phys. Rev. Lett. 95, 031101 (2005) · 10.1103/PhysRevLett.95.031101 · arXiv:astro-ph/0506500
3.
U. Hager et al.
Measurement of the ¹⁷O(p,γ)¹⁸F reaction rate at astrophysically relevant energies
Phys. Rev. C 85, 035803 (2012) · 10.1103/PhysRevC.85.035803
4.
A. Kontos, J. Görres, A. Best, M. Couder, R. deBoer, G. Imbriani, Q. Li, D. Robertson, D. Schürmann, E. Stech, E. Uberseder and M. Wiescher
Proton capture on ¹⁷O and its astrophysical implications
Phys. Rev. C 86, 055801 (2012); erratum Phys. Rev. C 88, 029905 (2013) · 10.1103/PhysRevC.86.055801 · arXiv:1210.7866
5.
D. A. Scott et al. (LUNA Collaboration)
First direct measurement of the ¹⁷O(p,γ)¹⁸F reaction cross section at Gamow energies for classical novae
Phys. Rev. Lett. 109, 202501 (2012) · 10.1103/PhysRevLett.109.202501 · arXiv:1210.6529LUNA
6.
A. Di Leva et al. (LUNA Collaboration)
Underground study of the ¹⁷O(p,γ)¹⁸F reaction relevant for explosive hydrogen burning
Phys. Rev. C 89, 015803 (2014) · 10.1103/PhysRevC.89.015803LUNA
7.
M. Q. Buckner, C. Iliadis, K. J. Kelly, L. N. Downen, A. E. Champagne, J. M. Cesaratto, C. Howard and R. Longland
High-intensity-beam study of ¹⁷O(p,γ)¹⁸F and thermonuclear reaction rates for ¹⁷O + p
Phys. Rev. C 91, 015812 (2015) · 10.1103/PhysRevC.91.015812
8.
R. M. Gesuè et al. (LUNA Collaboration)
First direct measurement of the 64.5 keV resonance strength in the ¹⁷O(p,γ)¹⁸F reaction
Phys. Rev. Lett. 133, 052701 (2024) · 10.1103/PhysRevLett.133.052701 · arXiv:2408.03015LUNA
9.
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

How to cite this page

J. Skowronski, ¹⁷O(p,γ)¹⁸F, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/17O-pg-18F.

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