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.
Highlights
Most neutron cross section measurements are made relative to the neutron cross section standards. 197Au(n,γ) is the only capture cross section standard
ND2019 used as a reference, and the traditionally adopted value for the Maxwellian averaged cross section (MACS)-30 was obtained by Ratynski & Käppeler, in an accurate activation measurement using a spherical segment gold sample [4]
In the case of Maxwellian Neutron Spectra (MNS) method the aperture of the neutron cone is larger than in quasi-Maxwellian neutron spectrum (QMNS) at 1912 keV, the correction due to flat sample and neutron scattering will become more important, obtaining kn = 1,75
Summary
Most neutron cross section measurements are made relative to the neutron cross section standards. 197Au(n,γ) is the only capture cross section standard. 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).
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