Measurement of the Tb159(n,γ) cross section at the CSNS Back-n facility

Abstract

The stellar ($n,\ensuremath{\gamma}$) cross section data for the mass numbers around $A\ensuremath{\approx}160$ are of key importance to nucleosynthesis in the main component of the slow neutron capture process, which occurs in the thermally pulsing asymptotic giant branch (TP-AGB). The new measurement of ($n,\ensuremath{\gamma}$) cross sections for $^{159}\mathrm{Tb}$ was performed using the ${\mathrm{C}}_{6}{\mathrm{D}}_{6}$ detector system at the back streaming white neutron beam line (Back-n) of the China spallation neutron source with neutron energies ranging from 1 eV to 1 MeV. Experimental resonance capture kernels are reported up to 1.2 keV neutron energy with this capture measurement. Maxwellian-averaged cross sections (MACS) are derived from the measured $^{159}\mathrm{Tb}(n,\ensuremath{\gamma})$ cross sections at $kT=5$--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 is also performed with the stellar evolution code mesa. Significant changes in abundances around $A\ensuremath{\approx}160$ are observed between the ENDF/B-VIII.0 and present measured rate of $^{159}\mathrm{Tb}(n,\ensuremath{\gamma})^{160}\mathrm{Tb}$ in the mesa simulation.