Cross section measurements of ¹⁵⁵︐¹⁵⁷Gd(n,γ ) induced by thermal and epithermal neutrons

Abstract

Neutron capture cross section measurements on ¹⁵⁵Gd and ¹⁵⁷Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n_TOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C₆D₆ liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for ¹⁵⁵Gd and ¹⁵⁷Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181 eV and 307 eV, respectively for ¹⁵⁵Gd and ¹⁵⁷Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2.01(28) x 10⁻⁴ and 2.17(41) x 10⁻⁴; average total radiative width of 106.8(14) meV and 101.1(20) meV and s-wave resonance spacing 1.6(2) eV and 4.8(5) eV for n + ¹⁵⁵Gd and n + ¹⁵⁷Gd systems, respectively.