| Popis: |
TENMAK D.N.3326 Thermal neutron cross section and resonance integral for the 139La(n,γ)140La reaction was measured by the activation method. The experimental samples with and without a cylindrical Cd shield case in 1 mm wall thickness were irradiated in an isotropic neutron field of the 241Am-Be neutron source. The extent of the nonideality of the epithermal neutron spectrum(i.e., α- shaping factor for 1 E1+α epithermal distribution) at the sample irradiation position was experimentally determined by the two-detector(Au and W foils) method, and it was found to be 0.560±0.002. The induced activities in the samples were measured by high resolution γ-ray spectrometry with a calibrated n-type Ge detector. Thermal neutron cross section for 2200 m/s neutrons and resonance integral for the 139La(n,γ)140La reaction has been obtained relative to the reference values, σ0=13.3±0.1 b and I0=14.0±0.3 b for the 55Mn(n,γ)56Mn reaction as a single comparator. The results corrected for gamma attenuation, thermal neutron and resonance neutron self-shielding effects and the effect of α- shaping factor on the resonance integral value of the (n,γ) reactions. For the conversion of the measured infinite dilution resonance integral, I(α) to the I0 for 1/E ideal epithermal neutron spectrum, the concept of effective resonance energy, Er described by De Corte for the Ryves’ method[1] has been used. By defining Cd cut-off energy 0.55 eV, the results obtained were: σ0=9.27 ± 0.37 b and I0=12.16 ± 0.60 b for the 139La(n,γ)140La reaction. These results are discussed and compared with previous measurements and the evaluated data in JEF-2.2, IAEA and JENDL-3.2. Thermal neutron cross section for 139La(n,γ)140La reaction is in good agreement with the recent measurements. There existed the discrepancies between present results and some of old experimental data for thermal cross section and resonance integral for this reaction is within about 6-40%. Turkish Atomic Energy Authority, [v.d.]…. |
