Measurement of the radiative neutron capture cross section of Pb-206 and its astrophysical implications
n TOF Collaboration
The (n,gamma) cross section of Pb-206 has been measured at the CERN n_TOF facility with high resolution in the energy range from 1 eV to 620 keV by using two optimized C6D6 detectors. In the investigated energy interval about 130 resonances could be observed, from which 61 had enough statistics to be reliably analyzed via the R-matrix analysis code SAMMY. Experimental uncertainties were minimized, in particular with respect to (i) angular distribution effects of the prompt capture gamma-rays, and to (ii) the TOF-dependent background due to sample-scattered neutrons. Other background components were addressed by background measurements with an enriched Pb-208 sample. The effect of the lower energy cutoff in the pulse height spectra of the C6D6 detectors was carefully corrected via Monte Carlo simulations. Compared to previous Pb-206 values, the Maxwellian averaged capture cross sections derived from these data are about 20% and 9% lower at thermal energies of 5 keV and 30 keV, respectively. These new results have a direct impact on the s-process abundance of Pb-206, which represents an important test for the interpretation of the cosmic clock based on the decay of U-238.