Measurement of the Ta-181(n, gamma) cross sections up to stellar s-process temperatures at the CSNS Back-n

The neutron capture cross section of Ta-181 is relevant to s-process of nuclear astrophysics, extraterrestrial samples analysis in planetary geology and new generation nuclear energy system design. The Ta-181(n, gamma) cross section had been measured between 1 eV and 800 keV at the backstreaming white neutron facility (Back-n) of China spallation neutron source(CSNS) using the time-of-flight (TOF) technique and C-6 D-6 liquid scintillator detectors. The experimental results are compared with the data of several evaluated libraries and previous experiments in the resolved and unresolved resonance region. Resonance parameters are extracted using the R-Matrix code SAMMY in the 1-700 eV region. The astrophysical Maxwell average cross section(MACS) from kT = 5 to 100 keV is calculated over a sufficiently wide range of neutron energies. For the characteristic thermal energy of an astrophysical site, at kT = 30keV the MACS value of Ta-181 is 834 +/- 75 mb, which shows an obvious discrepancy with the Karlsruhe Astrophysical Database of Nucleosynthesis in Stars (KADoNiS) recommended value 766 +/- 15 mb. The new measurements strongly constrain the MACS of Ta-181(n, gamma) reaction in the stellar s-process temperatures.