Resonance Analysis for Neutron Capture Cross Sections of Th-232

摘要

In recent years, a great interest has been taken in the thorium fuel cycle. The neutron capture reaction for ~(232)Th is very important to evaluate the ~(233)U production in the thorium fuel cycle. In the present study, we have carried out the resonance analysis of neutron capture cross sections of ~(232)Th obtained by using the Kyoto University Research Reactor Institute - Linear Accelerator (KURRI-LINAC). We performed the resonance analysis using the code SAMMY for the 10 resolved resonances in the energy range from 20 to 210 eV. The obtained parameters for the 69.2-, 113.1-, 120.9-and 170.4-eV resonances are in disagreement with the evaluated values, whereas the parameters for other six resonances were in general agreement. In order to verify the validity for the resonance analysis, we also investigated the neutron self-shielding and multiple-scattering effects on the neutron capture cross sections obtained for ~(232)Th samples with three different thicknesses. The correction factors were estimated by the Monte Carlo simulation using the evaluated cross sections in JENDL-4.0 and the cross section data revised by the present resonance analysis. The comparison between the capture cross sections corrected with the JENDL-4.0 is consistent with the resonance analysis results. Moreover, it was confirmed that the revised cross section data enable the correction factors to reproduce the experimental results for the 69.2- and 120.9-eV resonances. In the case of 170.4-eV resonance, the disagreement between the experimental results was not improved in this study. Therefore, further study is necessary to improve the resonance data.