Measurement of thermal neutron cross-section and resonance integral for 186W( n,γ) 187W reaction by the activation method using a single monitor

Abstract

The thermal neutron cross-section ( σ 0) and the resonance integral ( I 0) of the reaction 186W( n,γ) 187W were measured by the activation method using 55Mn as a single comparator. The diluted MnO 2 and WO 3 samples within and without a cylindrical Cd shield case were irradiated in an isotropic neutron field of the 241Am–Be neutron source. The γ-ray spectra from the irradiated samples were measured by high resolution γ-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 ( α) for epithermal neutron spectrum were taken into account in the determinations. The thermal neutron cross-section for 186W( n,γ) 187W 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 55Mn( n,γ) 56Mn reaction. The present value of 39.5±2.3 b for 186W( n,γ) 187W, 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 55Mn( n,γ) 56Mn monitor reaction using a 1/ E 1+ α epithermal neutron spectrum of the 241Am–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.