Measurement of the radiative neutron capture cross section of 206Pb and its astrophysical implications

TL;DR

This study precisely measured the neutron capture cross section of 206Pb across a wide energy range, providing new data that refine astrophysical models of element formation and cosmic chronometers.

Contribution

The paper presents the first high-resolution measurement of 206Pb(n, gamma) cross section from 1 eV to 600 keV, with improved accuracy over previous data, impacting astrophysical nucleosynthesis models.

Findings

Maxwellian averaged cross sections are about 20% lower at 5 keV.

Maxwellian averaged cross sections are about 9% lower at 30 keV.

Results influence the interpretation of the cosmic clock based on 238U decay.

Abstract

The (n, gamma) cross section of 206Pb has been measured at the CERN n_TOF facility with high resolution in the energy range from 1 eV to 600 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 208Pb 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 206Pb 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 206Pb, which represents an important test for the interpretation of the cosmic clock based on the decay of 238U.