Two absolute integral measurements of the ¹⁹⁷Au(n,γ) stellar cross-section and solution of the historic discrepancies

¹ Atomic, Molecular and Nuclear Physics Department, University of Granada, Spain
² Atomic, Molecular and Nuclear Physics Department, University of Seville, Spain

^* Corresponding author: jpraena@ugr.es

Published online: 30 September 2020

Abstract

The Maxwellian averaged cross section (MACS) for ¹⁹⁷Au(n,γ) is used in neutron capture cross section measurements as a reference for reactions important for astrophysics, reactor and dosimetry applications. The traditionally adopted value for this reference cross section, in the energy range relevant for astrophysical (3 < E _n < 200 keV), was obtained by Ratynski and Käppeler in 1988. However, the MACS calculated using the 2006 standards evaluation is approximately 6 % above the Ratynski and Käppeler (R&K) evaluation. Because of this discrepancy new experiments and reanalyses were done in an attempt to resolve the problem. In 2011 we started as well a series of integral experiments (activation) for determining the MACS-30 (kT=30 keV) of Au with two different Maxwellian neutron spectra: i) QMNS-25 (as R&K) and ii) MNS-30 (new method). Our results agree with those obtained with the standard evaluation. At present (2018), the updated MACS-30 has been included as standard. Here we present the results of our measurements and the reasons for the lower value of the R&K measurement.