Neon-22 captures a helium nucleus and keeps it, becoming magnesium-26. It competes with the neutron-releasing reaction on the same nucleus.
Every neon-22 nucleus that captures helium through this reaction is lost as a neutron source. At lower temperatures this capture is faster than the neutron-producing reaction, so it decides how much neon-22 is still left when the star becomes hot enough to release neutrons. It also adds magnesium-26 to the gas the star returns to the Galaxy.
Facts
- How well known
- The 830 keV resonance is measured to about 6%, but the lower-lying resonances are known only from indirect data and direct upper limits.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 10.615 MeV
- Gamow window
- 565 ± 130 keVAGB thermal pulse, 0.27 GK (Neutron sources of the s-process)
- 605 ± 145 keVmassive star, He core end, 0.3 GK (Neutron sources of the s-process)
- Kind
- Radiative capture
How it was measured
4 measurements, 2019–2022, 1 at LUNAShow the listHide the list
2019
LENA, TUNLTriangle Universities Nuclear Laboratory
Direct measurement at the surface · E(α,lab) = 0.83 MeV resonance
Implanted 22Ne target and γγ-coincidence detection; E(α,lab) = 835.2 ± 3.0 keV and ωγ = (4.6 ± 1.2)×10−5 eV, higher than earlier values but overlapping within the uncertainties. [1]
2020
Cyclotron Institute, Texas A&MTexas A&M University
Transfer reactions and ANCs · 22Ne(6Li,d) and 22Ne(7Li,t), 1.0 MeV/u 22Ne beam
Partial α widths of 26Mg resonances in the Gamow window; the (α,γ) rate differs significantly from earlier values. [2]
2022
LUNA 400 kVLaboratori Nazionali del Gran Sasso (INFN)
Direct measurement underground · E = 334 keV resonance
First direct limit, ωγ < 4.0×10−11 eV (90% CL), higher than most indirect limits but free of their model assumptions. [3]
2022
Nuclear Science Laboratory, Notre DameUniversity of Notre Dame
Direct measurement at the surface · E(α,lab) = 650 and 830 keV resonances
Implanted 22Ne targets; ωγ(830 keV) = 35 ± 4 µeV and the first direct upper limit for the 650 keV resonance. [4]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
7 datasets in 6 EXFOR entries, 1975–2022 · 1 without an energy range, not drawn
- Lowest energy in EXFOR
- 683 keV
- Wolke et al., 1989 · σ · O1122.002
- Distance from the Gamow peak
- Only the upper edge of the window
- E₀ = 564 keV, window 432–696 keV
- Rate from energies not in EXFOR
- 85%
- at T₉ = 0.27, smooth estimate · 85% of it lies below the lowest energy in EXFOR
1 resonance-strength datasets reach into this window: the smooth estimate does not count resonances.
- 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) |
|---|---|---|
| σ→Eₓpartial | 2 | 683 keV – 10.4 MeV |
| dσ/dΩangular distribution | 1 | 3.75 MeV – 13.3 MeV |
| ωγresonance strength | 3 | 283 keV – 707 keV |
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
The rate is dominated by low-energy resonances in 26Mg, chiefly those at E(α,lab) = 650 and 830 keV. For the 830 keV resonance Hunt et al. (2019) found ωγ = (4.6 ± 1.2)×10−5 eV at LENA, and Shahina et al. (2022) measured ωγ = 35 ± 4 µeV and give a weighted average with earlier measurements of 35 ± 2 µeV; for the 650 keV resonance they report an upper limit, ωγ < 0.15 µeV. At lower energies the resonance strengths come only from indirect data, and the literature values for the resonance at E = 334 keV (E(α,lab) ≈ 395 keV, Ex = 10949 keV) span a wide range.
LUNA set the first direct upper limit on it, ωγ < 4.0×10−11 eV at 90% confidence, with a windowless enriched 22Ne gas target and a 4π BGO summing detector at the 400 kV accelerator; the background in the region of interest was below 0.5 counts per day (Piatti et al. 2022). The authors propose to extend the approach to higher energies at the 3.5 MV machine of the Bellotti Ion Beam Facility (BIBF).
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.
Open questions
- The strengths of the resonances below 830 keV, in particular at E = 334 keV, where direct sensitivity must improve by orders of magnitude to reach the indirect estimates.
- Spin-parity assignments of the 26Mg states in the Gamow window, which decide whether a state can be populated in α capture.
Discussed on the open-questions page
Related reactions
References
- 1.
S. Hunt, C. Iliadis, A. E. Champagne, L. N. Downen, A. Cooper
New measurement of the E(α,lab) = 0.83 MeV resonance in 22Ne(α,γ)26Mg
Phys. Rev. C 99, 045804 (2019) · 10.1103/PhysRevC.99.045804
- 2.
H. Jayatissa, G. V. Rogachev et al.
Phys. Lett. B 802, 135267 (2020) · 10.1016/j.physletb.2020.135267 · arXiv:2001.08316
- 3.
D. Piatti et al. (LUNA Collaboration)
First direct limit on the 334 keV resonance strength in 22Ne(α,γ)26Mg reaction
Eur. Phys. J. A 58, 194 (2022) · 10.1140/epja/s10050-022-00827-2 · arXiv:2209.03051LUNA
- 4.
Shahina, J. Görres, D. Robertson, M. Wiescher et al.
Direct measurement of the low-energy resonances in 22Ne(α,γ)26Mg reaction
Phys. Rev. C 106, 025805 (2022) · 10.1103/PhysRevC.106.025805 · arXiv:2208.07885
- 5.
C. Angulo, M. Arnould, M. Rayet et al. (NACRE Collaboration)
A compilation of charged-particle induced thermonuclear reaction rates
Nucl. Phys. A 656, 3 (1999)
- 6.
P. Adsley et al.
Reevaluation of the 22Ne(α,γ)26Mg and 22Ne(α,n)25Mg reaction rates
Phys. Rev. C 103, 015805 (2021) · 10.1103/PhysRevC.103.015805 · arXiv:2005.14482
How to cite this page
J. Skowronski, 22Ne(α,γ)26Mg, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/22Ne-ag-26Mg.
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)