Measurement of thermal neutron cross-sections and resonance integrals for Ga-71(n, gamma)Ga-72 and As-75(n, gamma)As-76 by using Am-241-Be isotopic neutron source

摘要

Thermal neutron cross-sections and resonance integrals for the Ga-71(n,gamma)Ga-72 and As-75(n, gamma)(76) As reactions were measured by the activation method. The experimental samples with and without a cylindrical Cd shield case in I mm wall thickness were irradiated in an isotropic neutron field of the Am-241-Be neutron source. The induced activities in the samples were measured by high-resolution gamma-ray spectrometry with a calibrated reverse-electrode germanium detector. Thermal neutron cross-sections for 2200 m/s neutrons and resonance integrals for the Ga-71(n,gamma) Ga-72 and As-75(n, gamma)(76) As reactions have been obtained relative to the reference values, sigma(0) = 13.3 +/- 0.1 b and I-0 = 14.0 +/- 0.3 b for the Mn-55(n, gamma)(56) Mn reaction as a single comparator. The necessary correction factors for gamma attenuation, thermal neutron and resonance neutron self-shielding effects were taken into account in the determinations. By defining Cd cut-off energy 0.55 eV, the results obtained were: sigma(0) = 4.41 +/- 0.18 b and I-0 = 32.3 +/- 2.3 b for Ga-71(n, gamma)Ga-72, and sigma(0) = 4.15 +/- 0.24 b and I0 = 63.5 +/- 3.8 b for As-75(n, gamma)(76) As. These results are discussed and compared with previous measurements and the evaluated data in ENDF/B-VI and JENDL-3.2. Thermal neutron cross-sections for Ga-71(n, gamma)Ga-72 and As-75(n, gamma)(76) As reactions are in good agreement with the recent measurements. However, the discrepancies between present results and some of old experimental data for resonance integrals for both reactions are within about 8-58%. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 46]