Abstract
Cross section measurements have been performed at the time-of-flight facility GELINA to determine the average capture cross section for 197Au in the energy region between 3.5 keV and 84 keV. Prompt γ-rays, originating from neutron-induced capture events, were detected by two C6 D6 liquid scintillators. The sample was placed at about 13m distance from the neutron source. The total energy detection principle in combination with the pulse height weighting technique was applied. The energy dependence of the neutron flux was measured with a double Frisch-gridded ionization chamber based on the 10B(n,α) reaction. The data have been normalized to the well-isolated and saturated 197Au resonance at 4.9 eV. Special care was taken to reduce bias effects due to the weighting function, normalization, dead time and background corrections. The total uncertainty due to normalization, neutron flux and weighting function is 1.0%. An additional uncertainty of 0.5% results from the correction for self-shielding and multiple interaction events. Fluctuations due to resonance structures have been studied by complementary measurements at a 30m flight path station. The results reported in this work deviate systematically by more than 5% from the cross section that is recommended as a reference for astrophysical applications. They are about 2% lower compared to an evaluation of the 197Au(n, γ) cross section, which was based on a least squares fit of experimental data available in the literature prior to this work. The average capture cross section as a function of neutron energy has been parameterized in terms of average resonance parameters. Maxwellian average cross sections at different temperatures have been calculated.
Highlights
The neutron capture cross section of 197Au is used as a standard for neutron induced reaction cross section measurements at 0.0253 eV and in the energy range between 200 keV and 2.5 MeV
Cross section measurements have been performed at the time-of-flight facility GELINA to determine the average capture cross section for 197Au in the energy region between 3.5 keV and 84 keV
The first time dependent component, approximated by a power function, accounts for neutrons that are scattered inside the detector station and from neutrons scattered at other flight paths
Summary
The neutron capture cross section of 197Au is used as a standard for neutron induced reaction cross section measurements at 0.0253 eV and in the energy range between 200 keV and 2.5 MeV. In the energy region between 200 keV and 2.5 MeV the result of this evaluation is recommended as a reaction cross section standard with uncertainties between 1% and 4.2%. Between 3.5 keV and 200 keV the uncertainties for the recommended average cross section are between 0.84% and 2.3% The result of this evaluation will be referred to as the standard evaluation. Due to strong fluctuations resulting from resonance structures the evaluated cross section below 200 keV is not recommended for use as a standard. [1,2,3] are approximately 6% to 8% above the cross section adopted for astrophysical applications The latter is based on the data of Macklin et al [6,7] normalized to the results of activation measurements performed by Ratynski and Kappeler [5]. To study the impact of resonance fluctuations additional capture measurements on 197Au at a 30 m measurement station were carried out
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