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107Ag and 109Ag resonance parameters for neutron induced reactions below 1 keV

Neutron transmission and capture measurements have been performed at the time-of-flight (TOF) facility GELINA of the EC-JRC-Geel, using metallic discs of natural silver with different thicknesses. Resonances of neutron interactions with 107Ag and 109Ag were analysed in the energy region below 1 keV applying the Reich-Moore approximation of the R-Matrix theory. Discrepancies between the experimental data and calculations based on the neutron resonance parameters recommended in the main neutron cross section libraries (JEFF, ENDF/B, JENDL) were observed. Improved resonance parameters were determined by a resonance shape analysis using the REFIT code. The resonance energy, neutron (Γn) and radiation (Γγ) width were adjusted in a simultaneous fit to transmission and capture yield spectra below 100 eV. Above 100 eV fixed average radiation widths (Γγ107 = 140 meV, Γγ109 = 130 meV) were used and the neutron width Γn was adjusted to only the capture yield data. Capture resonance integral I0 were calculated from the parameters derived in this work (I0,107 = 101.20 b, I0,109 = 1515.24 b) and compared with those calculated using the cross sections recommended in the main libraries. Discrepancies in I0 for 107Ag are mainly due to difference in the parameters of the resonances at 16.4 eV, 41.6 eV, 173.9 eV and 202.8 eV. In case of 109Ag differences are mainly due to the difference in parameters of the resonance at 5.2 eV.