Neutron capture cross section measurements for 197Au from 3.5 to 84 keV at GELINA

Abstract

Abstract. Cross section measurements have been performed at the time-of-flight facility GELINA to determine the average capture cross section for 197 Au in the energy region between 3.5 keV and 84 keV. Prompt γ-rays, originating from neutron-induced capture events, were detected by two C 6D6 liquid scintillators. The sample was placed at about 13 m 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 10 B(n, α) reaction. The data have been normalized to the well-isolated and saturated197 Au 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 30 m 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 197 Au(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.

MEASUREMENT OF THE 197Au(n,gamma) STELLAR CROSS SECTION BY ACTIVATION

“…This value is in good agreement with n_TOF differential measurement (611±22) mb, the ENDF/B-VII.1 evaluation value (614 mb), a very recent TOF measurement performed with a truncated neutron spectrum from 3.5 to 84 keV at GELINA 613 mb [13], and it is higher than the reference Ratynski & Käppeler activation measurement [5]. Our experimental cross section at kT=25 keV, = (645±25) mb, is also consistent with the result provided in recent activation measurements, (616±17) mb [12].…”

The new KADoNiS v1.0 and its influence on the s-process

“…However, recent time-of-flight measurements at n_TOF [21,22] and GELINA [23] revealed a 5% higher MACS at kT = 30 keV, in perfect agreement with the ENDF/B-VII.1 evaluation [12]. Including these measurements we have re-evaluated the 197 Au(n, γ) cross sections used in the KADoNiS database.…”

“…The new recommended cross section for the astrophysical energy region was derived between kT= 5 and 50 keV by the weighted average of the GELINA measurement and the n_TOF measurement. The uncertainty in this energy range was taken from [23]. For the energies between kT = 60-100 keV we used the average of the recent libraries (JEFF-3.2, JENDL-4.0, ENDF/B-VII.1) and the uncertainty from the standard deviation given in JEFF-3.2 and ENDF/B-VII.1.…”

Neutron capture cross sections of 69Ga and 71Ga at 25 keV and Epeak = 90 keV

“…Table 3 compares the results to the MACSs from KADoNiS v0.3 [7], which were renormalized with the 197 Au cross section value from Ref. [12]. The measured value for 69 Ga is about 30% higher than the evaluated value, the measured value for 71 Ga is about 20% lower.…”

“…The neutron capture cross sections at k B T = 25 keV can be calculated from the ratios using the MACS of 197 Au(n,γ ) at 25 keV (683 mb), which was taken from Ref. [12]. Table 3 compares the results to the MACSs from KADoNiS v0.3 [7], which were renormalized with the 197 Au cross section value from Ref.…”