Radioactive thulium-171 captures a neutron. Measured for the first time in 2020, both by time of flight and by activation, it turned out to capture 2.6 times less readily than the general-purpose libraries JEFF-3.3 and ENDF/B-VIII said.
Thulium-171 lives about two years in the laboratory. In an AGB star it either decays into ytterbium-171 or captures a neutron and moves on to thulium-172, so how readily it captures sets how much ytterbium-171 the star makes. Stardust grains from AGB stars, found in meteorites, record that amount, and they can be compared with the models only if the capture is known.
Facts
- How well known
- Measured for the first time in 2020, at CERN and in Israel, to about 10%.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 6.235 MeV
- Half-life of 171Tm
- 1.92 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.
- Product 172Tm
- radioactive, t½ = 2.65 d
- Kind
- Radiative capture
On the timeline
How it was measured
2 measurements, 2020Show the listHide the list
2020
n_TOF, CERNCERN
Neutron beams and time of flight · resolved resonances (neutron energy)
First resonance parameters of 171Tm, on a sample made at the ILL; the MACS extrapolated from them agrees with the activation value. [1]
2020
SARAF and LiLiTSoreq Nuclear Research Center
Activation · quasi-Maxwellian kT ≈ 30 keV
MACS at kT = 30 keV of 384(40) mb, 2.6 times below the JEFF-3.3 and ENDF/B-VIII evaluations. [1]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
21 datasets in 10 EXFOR entries, 1967–2020 · 8 without an energy range, not drawn
- Lowest energy in EXFOR
- 25.1 meV
- Heftrich et al., 2019 · σ · 23540.002
- Maxwellian averages measured
- 6 sets
- kT from 25 keV to 43 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 | 25.1 meV – 192 keV |
| MACSMaxwellian average | 6 | 25 keV – 43 keV |
| …other | 4 | 995 meV – 994 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: Measured in 2020 by time of flight at n_TOF and by activation at SARAF; the MACS at 30 keV is known to about 10%.
The sample was produced at the ILL high-flux reactor and separated at PSI. At n_TOF the capture yield gave the first set of resonance parameters of 171Tm; at SARAF the liquid-lithium target LiLiT provided a quasi-Maxwellian spectrum for an activation that gave the MACS at kT = 30 keV directly, 384(40) mb, in agreement with the time-of-flight estimate. The value is 2.6 times lower than JEFF-3.3 and ENDF/B-VIII, 25% lower than Bao et al. (2000) and 1.6 times higher than KADoNiS v1; with it, AGB models make more 171Yb, closer to the presolar SiC grains (Guerrero et al. 2020).
Evaluations
Compilations that combine the data into a recommended rate.
Related reactions
References
- 1.
C. Guerrero et al. (n_TOF Collaboration)
Neutron capture on the s-process branching point 171Tm via time-of-flight and activation
Phys. Rev. Lett. 125, 142701 (2020) · 10.1103/PhysRevLett.125.142701
- 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, 171Tm(n,γ)172Tm, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/171Tm-ng-172Tm.
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