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Reaction atlas · Neutron sources

Radiative capture · Neutron poisons

22Ne(n,γ)23Ne

: neon‑22 + neutron → neon‑23 + gamma rayHow to read the notation

On this page

Neon-22, the fuel of the neutron source in massive stars, also captures some of the neutrons that it releases.

In massive stars nearly all neutrons come from 22Ne(α,n)25Mg. Neon-22 is far more abundant than iron, so even though a single neon nucleus is very unlikely to capture a neutron, together they take a noticeable share. Each neutron captured by neon is lost to the heavy elements. The product, neon-23, decays within a minute to sodium-23.

Facts

How well known
Measured, but a 2014 reanalysis changed the values for the neon isotopes substantially from the older compilations.
Live evaluation
No live evaluation yet · Evaluations
Reaction rates
Explore the rates →
Q-value · energy released
5.201 MeV
Thermal energy kT
about 26 keV, the energy of a gas at 300 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 23Ne
radioactive, t½ = 37.1 s
Kind
Radiative capture

How it was measured

2 measurements, 2002–2003Show the list
  1. 2002

    Activation · keV region

    Capture on 22Ne measured together with 40Ar and the krypton isotopes 78,80,84,86Kr. [1]

  2. 2003

    Tokyo Institute of Technology, 3.2 MV Pelletron

    Neutron beams and time of flight · keV neutrons, prompt capture γ-rays

    Discrete γ-rays from the capture states of 20Ne and 22Ne observed for the first time; non-resonant direct p-wave capture identified; MACS larger than earlier values. [2]

Measurements (EXFOR)

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

46 datasets in 11 EXFOR entries, 1952–2009 · 14 without an energy range, not drawn

massive star, core helium burning, kT = 25.9 keV

Lowest energy in EXFOR
2.55 keV
Winters et al., 1988 · σ · 13139.008
Maxwellian averages measured
25 sets
kT from 1 keV to 250 keV
Rate from energies not in EXFOR
2.3%
at kT = 25.9 keV, smooth estimate
10 meV1 eV100 eV10 keV1 MeVEnergy, or kT for a Maxwellian average (keV)kT = 25.9 keVσσ→EₓMACSother
  • Energies that matter at kT = 25.9 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
The datasets of the gap map, by quantity
QuantityDatasetsE_cm range (keV)
σcross section324.2 meV – 206 keV
σ→Eₓpartial125.3 keV – 46.6 keV
MACSMaxwellian average251 keV – 250 keV
…other324.2 meV – 1.65 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: The 2014 R-matrix reanalysis changed the stellar rates of the neon isotopes substantially compared with earlier compilations.

The Maxwellian-averaged cross section of 22Ne is tiny, but its abundance in helium-burning matter makes it a significant poison. It was measured by activation together with other noble-gas isotopes in the keV region (Beer et al. 2002) and with the prompt capture γ-rays at the Tokyo Institute of Technology, where the discrete γ-rays from the capture states were observed for the first time and the direct p-wave capture was identified (Tomyo et al. 2003). Heil et al. (2014) re-analysed the keV resonance data of the three stable neon isotopes with the R-matrix code SAMMY, adding direct-capture components, and gave new Maxwellian-averaged cross sections; they found that earlier work had grossly overestimated the stellar rates of 20Ne and 21Ne (an erratum appeared in 2015).

Evaluations

Compilations that combine the data into a recommended rate.

  • —M. Heil et al., Phys. Rev. C 90, 045804 (2014) [3]
  • —Z. Y. Bao et al., At. Data Nucl. Data Tables 76, 70 (2000) [4]
  • —I. Dillmann et al., Proc. Int. Conf. on Nuclear Data for Science and Technology 2007 (EDP Sciences, 2008), p. 575 [5]

Related reactions

References

  1. 1.

    H. Beer, P. V. Sedyshev, W. Rochow, P. Mohr, H. Oberhummer

    Neutron capture measurements of the noble gas isotopes 22Ne, 40Ar and 78,80,84,86Kr in the keV energy region

    Nucl. Phys. A 705, 239 (2002)

  2. 2.

    A. Tomyo, Y. Nagai, Y. Nobuhara, T. Shima, H. Makii, K. Mishima, M. Igashira

    Neutron capture cross section measurement of 20,22Ne for stellar nucleosynthesis

    Nucl. Phys. A 718, 527c (2003)

  3. 3.
  4. 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. 5.

    I. Dillmann et al.

    New stellar (n,γ) cross sections and the "Karlsruhe Astrophysical Database of Nucleosynthesis in Stars"

    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, 22Ne(n,γ)23Ne, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/22Ne-ng-23Ne.

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

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