Study on Measurements of Nuclear Data for Transmutation of Actinide Elements

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Studies on fission cross section measurements of Np-237 and Am-241 for tranmutation were performed through the Kyoto University Lead Slowing-down Spectrometer (KULS) coupled to the 46 MeV electron linear accelerator (linac). The characteristics of the KULS were firstly obtained for (1) the relation between neutron slowing-down time and energy, (2) energy resolution, and (3) neutron energy spectrum, by the MCNP code and by the experiments using neutron resonance filters. Then, the KULS was applied to the fission neutron cross section measurements of Np-237 and Am-241 relative to that of U-235 from about 1 eV to about 10 keV with energy resolution (dE/E) of about 40 %. Although the shape of the present cross section of Np-237 agrees with that measured by Plattard et al. and with those in ENDF/B-VI and JENDL-3, the absolute values of above three are from 3 to 4 times smaller than those of the present data. However, the measurement by Hoffman et al.is rather closer to the present result. For Am-241, the absolute values of the evaluated data and the Dabbs' measurementare are 3 times lower than the present data, which are rather closer to those measured by Gayther et al.and Bowman et al.above a few tens of eV.For the ^<237>Np(n, gamma)^<238>Np reaction, thermal reutron cross section (158(〕SY.+-.〔)3 b) and the resonance integral (652(〕SY.+-.〔)24 b) were measured with the standard Maxwellian and the 1/E neutron spectrum fields, respectively. Thermal neutron cross sections appeared in ENDF/B-V and JENDL-3 are larger by 7 to 15 % than the present value. For the resonance integral, the evaluated data are in good agreement with the present value.