Radioactive zirconium-93 captures a neutron. It lives so long that in a star it behaves almost like a stable nucleus; what is left of it decays later into niobium.
Zirconium-93 lives about 1.6 million years, far longer than the wait between two neutron captures, so in an AGB star it captures neutrons and the path continues to zirconium-94. The zirconium-93 still left when the star throws off its envelope decays afterwards into niobium-93, the only stable isotope of niobium. Its capture rate therefore matters both for the zirconium isotopes and for the niobium the s-process makes.
Facts
- How well known
- Measured at CERN at low energies only; at the higher energies of a star it still rests on estimates.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 8.219 MeV
- Half-life of 93Zr
- 1.61 million yr
- Measured in the laboratory; in a star, thermally excited states and ionization can change it. It decides how often this nucleus decays before it captures a neutron.
- Thermal energy kT
- about 8–23 keV, the energy of a gas at 90–270 million kelvin
By stellar site
- 7.8 keVAGB 13C pocket, 90 MK
- 23 keVAGB thermal pulse, 0.27 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.
- Kind
- Radiative capture
How it was measured
1 measurement, 2013Show the listHide the list
2013
n_TOF, CERNCERN
Neutron beams and time of flight · resolved resonances up to 8 keV (neutron energy)
Radioactive 93Zr sample; capture widths about 14% smaller than in an earlier experiment. [1]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
17 datasets in 8 EXFOR entries, 1955–2016 · 7 without an energy range, not drawn
- Lowest energy in EXFOR
- No measurement counts
- No dataset here passes the rule for a measurement (“How these numbers are made”).
- Maxwellian averages measured
- 4 sets
- kT from 5 keV to 30 keV
- Rate from energies not in EXFOR
- 100%
- at kT = 7.76 keV, smooth estimate
- Energies that matter at kT = 7.76 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 | 24.7 meV – 7.42 MeV |
| MACSMaxwellian average | 4 | 5 keV – 30 keV |
| …other | 3 | 495 meV – 7.42 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: Resonances measured at n_TOF up to 8 keV; the higher energies that matter at kT = 30 keV come from evaluations.
The capture on the radioactive 93Zr was measured at n_TOF and analysed in resolved resonances up to 8 keV neutron energy; the capture widths came out about 14% smaller than in an earlier experiment (Tagliente et al. 2013). Above 8 keV the stellar cross section still rests on evaluations, so the MACS at kT = 30 keV is only partly measured.
Evaluations
Compilations that combine the data into a recommended rate.
Related reactions
References
- 1.
G. Tagliente et al. (n_TOF Collaboration)
The 93Zr(n,γ) reaction up to 8 keV neutron energy
Phys. Rev. C 87, 014622 (2013) · 10.1103/PhysRevC.87.014622
- 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, 93Zr(n,γ)94Zr, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/93Zr-ng-94Zr.
Cite the date you used; it is the last change to this page.
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