Thermal ($n,\gamma$) cross section and resonance integral of ${}^{171}\mathrm{Tm}$

Background: About 50% of the heavy elements are produced in stars during the slow neutron capture process. The analysis of branching points allows us to set constraints on the temperature and the neutron density in the interior of stars.

Purpose: The temperature dependence of the branch point ${}^{171}\mathrm{Tm}$ is weak. Hence, the ${}^{171}\mathrm{Tm}$ neutron capture cross section can be used to constrain the neutron density during the main component of the $s$ process in thermally pulsing asymptotic giant branch (TP-AGB) stars.

Methods: A ${}^{171}\mathrm{Tm}$ sample produced at the ILL was activated with thermal and epithermal neutrons at the TRIGA research reactor at the Johannes Gutenberg-Universität Mainz.

Results: The thermal neutron capture cross section and the resonance integral have been measured for the first time to be ${\sigma }_{\text{th}}=9.9\pm 0.9\text{b}$ and ${\sigma }_{\text{RI}}=193\pm 14\text{b}$.

Conclusions: Based on our results, new estimations of the direct capture components' impact on the Maxwellian-nAveraged cross sections (MACS) are possible.

Figure 1

The $s$-process reaction path between Er and Yb depicted by grey arrows. Secondary paths are represented by dashed lines. The radioactive isotopes ${}^{170}\mathrm{Tm}$ and ${}^{171}\mathrm{Tm}$ act as branch points and can be used to study the neutron density during the main component of the $s$ process.

Figure 2

Spectrum obtained for the ${}^{171}\mathrm{Tm}$ sample characterization. Aside from the ${}^{171}\mathrm{Tm} \gamma$ line at 66.7 keV, only x rays of the Tm isotopes are visible.

Figure 3

$\gamma$-spectra from the ${}^{171}\mathrm{Tm}$ sample after the activations with (black) and without (red) Cd shielding. ${}^{172}\mathrm{Tm}$ lines are marked (blue arrows). Activated sodium was the major background source.