Nickel-62 captures a neutron. In massive stars this capture is one of the steps that hold back the weak s-process, and it affects what is made after it.
In massive stars there are too few neutrons per iron seed for the s-process to reach far, and the flow of matter stays in the region from iron to strontium. There, each capture with a small cross section holds back the flow and lowers the production of every heavier nucleus. Nickel-62 is one of these steps, which is why its stellar cross section, in particular at the high temperatures of carbon-burning shells, changes the predicted production of the heavier nuclei, and of copper in particular.
Facts
- How well known
- Known to about 5%, from neutron-beam measurements at CERN, which lowered the value for the hottest burning in massive stars.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 6.838 MeV
- Thermal energy kT
- about 26–90 keV, the energy of a gas at 300–1000 million kelvin
By stellar site
- 26 keVmassive star, core helium burning, 0.3 GK
- 90 keVmassive star, shell carbon burning, 1.04 GK
- 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 63Ni
- radioactive, t½ = 101 yr
- Kind
- Radiative capture
How it was measured
1 measurement, 2014Show the listHide the list
2014
n_TOF, CERNCERN
Neutron beams and time of flight · resonances up to 200 keV (neutron energy)
42 resonances analysed; MACS for kT = 5–100 keV with 4.5% total uncertainty, up to a factor 1.6 below KADoNiS at high kT. [1]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
56 datasets in 27 EXFOR entries, 1952–2014 · 23 without an energy range, not drawn
- Lowest energy in EXFOR
- 24.6 meV
- Cote et al., 1964; Doilnitsyn, 1965; Sims et al., 1970; Alpizar-Vicente et al., 2008 · dσ/dΩ · 13816.006
- Maxwellian averages measured
- 15 sets
- kT from 5 keV to 100 keV
- Rate from energies not in EXFOR
- < 0.01%
- 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 | 5 | 24.6 meV – 358 keV |
| dσ/dΩangular distribution | 1 | 24.9 meV – 24.9 meV |
| ωγresonance strength | 2 | 3.94 keV – 4.53 keV |
| MACSMaxwellian average | 15 | 5 keV – 100 keV |
| …other | 10 | 24.6 meV – 295 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
How well known, in detail: Known to 4.5% at kT = 30 keV from n_TOF; the n_TOF data lowered the cross section at the higher temperatures of carbon burning by up to a factor 1.6.
At n_TOF the capture kernels of 42 resonances of 62Ni were analysed up to 200 keV, and Maxwellian-averaged cross sections were calculated for kT = 5–100 keV with a total uncertainty of 4.5%. They agree with the KADoNiS value at kT = 30 keV but are up to a factor 1.6 lower at higher temperatures, which matters for shell carbon burning at kT ≈ 90 keV (Lederer et al. 2014).
Evaluations
Compilations that combine the data into a recommended rate.
Related reactions
References
- 1.
C. Lederer et al. (n_TOF Collaboration)
62Ni(n,γ) and 63Ni(n,γ) cross sections measured at the n_TOF facility at CERN
Phys. Rev. C 89, 025810 (2014) · 10.1103/PhysRevC.89.025810 · arXiv:1403.4778
- 2.
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
- 3.
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, 62Ni(n,γ)63Ni, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/62Ni-ng-63Ni.
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