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 listHide the list
2002
Activation · keV region
Capture on 22Ne measured together with 40Ar and the krypton isotopes 78,80,84,86Kr. [1]
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
- 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
| Quantity | Datasets | E_cm range (keV) |
|---|---|---|
| σcross section | 3 | 24.2 meV – 206 keV |
| σ→Eₓpartial | 1 | 25.3 keV – 46.6 keV |
| MACSMaxwellian average | 25 | 1 keV – 250 keV |
| …other | 3 | 24.2 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.
Related reactions
References
- 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.
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.
M. Heil et al.
Stellar neutron capture cross sections of 20,21,22Ne
Phys. Rev. C 90, 045804 (2014) · 10.1103/PhysRevC.90.045804
- 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.
I. Dillmann et al.
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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