Measurement of the $^{159}$Tb(n, $\gamma$) cross section at the CSNS Back-n facility

TL;DR

This study measured the neutron capture cross section of $^{159}$Tb at the CSNS facility, providing data crucial for understanding nucleosynthesis in stars and revealing discrepancies with existing nuclear data libraries.

Contribution

The paper presents new experimental cross section data for $^{159}$Tb(n,γ), improving the accuracy of stellar nucleosynthesis models and highlighting differences with standard nuclear data evaluations.

Findings

Measured resonance capture kernels up to 1.2 keV.

Derived Maxwellian-averaged cross sections consistent with some databases.

Identified significant differences in stellar abundance predictions using different data sets.

Abstract

The stellar (n, $\gamma$) cross section data for the mass numbers around A $\approx$ 160 are of key importance to nucleosynthesis in the main component of the slow neutron capture process, which occur in the thermally pulsing asymptotic giant branch (TP--AGB). The new measurement of (n, $\gamma$) cross sections for $^{159}$Tb was performed using the C$_6$D$_6$ detector system at the back streaming white neutron beam line (Back-n) of the China spallation neutron source (CSNS) with neutron energies ranging from 1 eV to 1 MeV. Experimental resonance capture kernels were reported up to 1.2 keV neutron energy with this capture measurement. Maxwellian-averaged cross sections (MACS) were derived from the measured $^{159}$Tb (n, $\gamma$) cross sections at $kT$ = 5 $\sim$ 100 keV and are in good agreement with the recommended data of KADoNiS-v0.3 and JEFF-3.3, while KADoNiS-v1.0 and ENDF-VIII.0 significantly overestimate the present MACS up to 40$\%$ and 20$\%$, respectively. A sensitive test of the s-process nucleosynthesis was also performed with the stellar evolution code MESA. Significant changes in abundances around A $\approx$ 160 were observed between the ENDF/B-VIII.0 and present measured rate of $^{159}$Tb(n, $\gamma$)$^{160}$Tb in the MESA simulation.