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Reaction atlas · s-process

Radiative capture · Main component (AGB stars)

171Tm(n,γ)172Tm

: thulium‑171 + neutron → thulium‑172 + gamma rayHow to read the notation

On this page

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

  1. 1987Stardust from AGB stars in a meteorite

How it was measured

2 measurements, 2020Show the list
  1. 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]

  2. 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

Temperature
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
10 meV1 eV100 eV10 keV1 MeVEnergy, or kT for a Maxwellian average (keV)kT = 7.76 keVσMACSother
  • 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
The datasets of the gap map, by quantity
QuantityDatasetsE_cm range (keV)
σcross section325.1 meV – 192 keV
MACSMaxwellian average625 keV – 43 keV
…other4995 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.

  • —Z. Y. Bao et al., At. Data Nucl. Data Tables 76, 70 (2000) [2]
  • —I. Dillmann et al., Proc. Int. Conf. on Nuclear Data for Science and Technology 2007 (EDP Sciences, 2008), p. 575 [3]

Related reactions

References

  1. 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. 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. 3.

    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, 171Tm(n,γ)172Tm, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/171Tm-ng-172Tm.

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

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