Thermal neutron cross-section and resonance integral of the Mo-98(n,gamma)Mo-99 reaction

Abstract

We measured the thermal neutron cross-section and the resonance integral of the Mo-98(n,gamma)(99) Mo reaction by the activation method using a Au-197(n,gamma)Au-198 monitor reaction as a single comparator. The high-purity natural Mo and Au metallic foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a calibrated p-type high-purity Ge detector. The necessary correction factors for the gamma-ray attenuation (F-g), the thermal neutron self-shielding (G(th)) and the resonance neutron self-shielding (G(epi)) effects, and the epithermal neutron spectrum shape factor (alpha) were taken into account. In addition, for the Mo-99 activity measurements, the correction for true coincidence summing effects was also taken into account. The thermal neutron cross-section for the Mo-98(n,gamma)Mo-99 reaction has been determined to be 0.136 +/- 0.007 barn, relative to the reference value of 98.65 +/- 0.09 barn for the Au-197(n,gamma)(198) Au reaction. The present result is, in general, in good agreement with most of the experimental data and the recently evaluated values of ENDF/B-VII.0, JENDL-3.3, and JEF-2.2 by 5.1% (1 sigma). By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the Mo-98(n,gamma)Mo-99 reaction is 7.02 +/- 0.62 barn, which is determined relative to the reference values of 1550 +/- 28 barn for the Au-197(n,gamma)Au-198 reaction. The present resonance integral value is in general good agreement with the previously reported data by 8.8% (1 sigma). (C) 2008 Elsevier B.V. All rights reserved.