Radioactive samarium-151 captures a neutron. It is a classic branch point of the s-process, whose capture has been measured on a radioactive sample.
Samarium-151 lives about 95 years in the laboratory. In an AGB star it either captures a neutron, continuing the main path to samarium-152, or decays into europium-151, opening a side path through the europium isotopes. Its decay in a star depends on the temperature, so the share of the two paths depends both on the neutron density and on how hot the star is. Comparing the predicted and the observed abundances of the samarium, europium and gadolinium isotopes in the Solar System therefore tests the conditions inside the stars that made them.
Facts
- How well known
- Measured on radioactive samples at CERN and Karlsruhe; how fast samarium-151 decays in a hot star is a separate question.
- Live evaluation
- No live evaluation yet · Evaluations
- Reaction rates
- Explore the rates →
- Q-value · energy released
- 8.258 MeV
- Half-life of 151Sm
- 94.6 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
On the timeline
How it was measured
2 measurements, 2004–2006Show the listHide the list
2004
n_TOF, CERNCERN
Neutron beams and time of flight · 1 eV – 1 MeV (neutron energy)
Radioactive sample; MACS at kT = 30 keV of 3100 ± 160 mb, well above the earlier theoretical estimates. [1]
2006
Karlsruhe Van de GraaffKernforschungszentrum Karlsruhe (now Karlsruhe Institute of Technology)
Neutron beams and time of flight · keV neutrons, 4π BaF2 detector
Stellar capture cross section of the branch point measured with the Karlsruhe 4π barium fluoride array. [2]
Measurements (EXFOR)
Every dataset EXFOR holds for this reaction, drawn by the energies it covers, against the energies a star uses.
25 datasets in 10 EXFOR entries, 1950–2008 · 10 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
- 6 sets
- kT from 5 keV to 100 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 | 2 | 25.1 meV – 25.1 meV |
| MACSMaxwellian average | 6 | 5 keV – 100 keV |
| …other | 7 | 25.1 meV – 982 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 at n_TOF and at Karlsruhe with radioactive samples; the temperature dependence of the stellar decay rate remains a separate input.
At n_TOF the cross section was measured from 1 eV to 1 MeV on a radioactive 151Sm sample; the Maxwellian-averaged cross section at kT = 30 keV, 3100 ± 160 mb, is significantly larger than the theoretical predictions used before (Abbondanno et al. 2004). At Karlsruhe the stellar cross section was measured with the 4π BaF2 detector and neutrons from the 3.7 MV Van de Graaff (Wisshak et al. 2006). The branchings at 147Nd, 147Pm, 148Pm and 151Sm together determine the abundances of the s-only isotopes 148Sm and 150Sm, which are shielded from the r-process by 148Nd and 150Nd (Käppeler et al. 2011).
Evaluations
Compilations that combine the data into a recommended rate.
Related reactions
References
- 1.
U. Abbondanno et al. (n_TOF Collaboration)
Phys. Rev. Lett. 93, 161103 (2004) · 10.1103/PhysRevLett.93.161103
- 2.
K. Wisshak, F. Voss, F. Käppeler, M. Krtička, S. Raman, A. Mengoni, R. Gallino
Stellar neutron capture cross section of the unstable s-process branching point 151Sm
Phys. Rev. C 73, 015802 (2006) · 10.1103/PhysRevC.73.015802
- 3.
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
- 4.
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
- 5.
F. Käppeler, R. Gallino, S. Bisterzo, W. Aoki
The s process: nuclear physics, stellar models, and observations
Rev. Mod. Phys. 83, 157 (2011) · 10.1103/RevModPhys.83.157 · arXiv:1012.5218
How to cite this page
J. Skowronski, 151Sm(n,γ)152Sm, in Reaction atlas, 2026-10-12, https://jskowron.eu/atlas/151Sm-ng-152Sm.
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