ANNALS OF NUCLEAR ENERGY, vol.31, no.11, pp.1285-1297, 2004 (SCI-Expanded)
186 The thermal neutron cross-section (sigma(0)) and the resonance integral (I-0) of the reaction (186W)(n: gamma)W-187 were measured by the activation method using Mn-55 as a single comparator. The diluted MnO2 and WO3 samples within and without a cylindrical Cd shield case were irradiated in an isotropic neutron field of the Am-241-Be neutron source. The gamma-ray spectra from the irradiated samples were measured by high resolution gamma-ray spectrometry with a calibrated high purity Ge detector. The necessary correction factors for gamma ray attenuation, thermal and resonance neutron self-shielding effects, and the shape factor (alpha) for epithermal neutron spectrum were taken into account in the determinations. The thermal neutron cross-section for W-186(n, gamma)W-187 reaction has been determined to be 39.5 +/- 2.3 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross-section value of 13.3 +/- 0.1 b for the Mn-55(n, gamma)Mn-56 reaction. The present value of 39.5 +/- 2.3 b for W-186(n, gamma)W-187, in general is in good agreement with most of experimental data and evaluated ones in ENDF/B-VI and JENDL-3.2 within the limits of error. The resonance integral has also been measured relative to the reference value of 14.0 +/- 0.3 b for the Mn-55 (n, gamma)Mn-56 monitor reaction using a I/E1+x epithermal neutron spectrum of the Am-241-Be neutron source. By defining Cd cut-off energy 0.55 eV, the resonance integral obtained was 493 40 b. The existing experimental and evaluated data for the resonance integral are distributed from 290 to 534 b. The present resonance integral value agrees with some previously reported values. (C) 2004 Elsevier Ltd. All rights reserved.