Measurement of the ratios of the237Np and241Am capture cross-sections to the235U fission cross-section by the reactivity method

Abstract

The aim of the present work is to check the neutron capture cross-sections by the nuclei 237Np and 241Am by comparing the calculated values of the fission reaction rates and of the central reactivity coefficients with those measured on critical assemblies. A similar method was previously used to measure the ratio of the capture and fission cross-sections, ct = ael~r f for 239pu and 235U [ 1, 2]. The fission and capture cross-sections of 235U have been well studied over the last 20 years and their error is estimated as roughly 2 %, whereas the cross-sections of 237Np and 24 tam are known with a substantially higher error of 5-10%. It was therefore decided to carry out a direct comparison of the measured and calculated ratios of the average fission cross-sections (i is an index denoting the element):and of the ratios of the central reactivity coefficients l)i/p 5 for which, neglecting a small retardation term, one can write

Measurement and Analysis of 241Am Fission Rate Ratio Relative to 235U Fission Rate in Thermal Neutron Systems Using Kyoto University Critical Assembly.

“…Therefore, it is desirable to examine the evaluated data through systematic comparison with integral experiments. Although extensive research on americium transmutation and incineration has been performed, [9][10][11][12][13][14] integral experiments directly aimed for the assessment of americium cross section data are rather scarce [15][16][17][18] and are mainly performed in fast neutron systems. The series of integral experiments for…”