Study on Measurements of Nuclear Data for Transmutation of Actinide Elements using Lead Slowing-down Spectrometer

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A lead slowing-down spectrometer was installed coupled to the 46 MeV electron linac at Research Reactor Institute, Kyoto University (KURRI). Characteristics of the Kyoto University Lead Slowing-down Spectrometer (KULS) were measured for (1) the relation between neutron slowing-down time t (mus) and energy E (keV) (E=190/t^2 in Bi hole and E=156/t^2 in Pb hole), (2) the energy resolution (-40% in Bi and Pb holes), and (3) the neutron energy spectrum by the neutron TOF method. The results obtained by the MCNP code were in general agreement with these experimental ones.The KULS has been applied to the fission cross section measurements of Am-241, Am-243 and Am-242m relative to that of U-235 from -0.1 eV to -10 keV,making use of the back-to-back type double fission chambers. For Am-214, Dabbs and ENDF/B-VI data are in good agreement with the present measurement. The JEND L-3.2 data are smaller by a factor of 2 between 10 and 200 eV.The ENDF/B-VI data for Am-243 are lower between 15 and 60 eV,and the JENDL-3.2 are lower in general above 100 eV.It has been found that the preliminary result for the Am-242m (n, f) reaction is close to the ENDF/B-VI and the JENDL-3.2 data. Thermal neutron cross sections for Am-241 and Am-243 have also been measured in a standard Maxwellian distribution spectrum field.Finally, aiming at the measurement of capture cross section for MA nuclides, the experimental investigation for Np-237 sample (-2 mg) has been performed with the KULS.Due to the comparable background counts to the foreground ones, the capture events from the sample have scarecely been detected with an Ar-gas proportional counter.