A least-squares fit of thermal data for fissile nuclei

A consistent set of 2200 m s−1 neutron cross sections, Westcott g-factors and fission-neutron yields have been developed and evaluated for 233U, 235U, 239Puand 241Pu. Auxiliary parameters such as 233U, 234U and 239Pu half-lives and 252Cf v values are also presented. All available relevant experimental data on fission, absorption, capture, total and scattering cross sections were revised using the most up-to-date reported standards. The latest Cf v data as well as the corrected vp (prompt) ratios of the above four nuclei were included in the study. The half-lives of the U and Pu nuclides have been reevaluated and were used to reassess experimental data which depended on the α-counting technique. A least-squares fitting program (lsf) was used to obtain a best overall fit and provide an estimate of the sensitivity of the parameters to the quoted uncertainties in experimental data. The recommended fissile thermal parameters listed in Table 36 now constitute a self-consistent set. Problems encountered in earlier evaluations have been found not to be significant in casting any doubts on the consistency of certain types of input data (such as v measurements and observations made in pile and Maxwellian neutron spectra) with the main body of input data. The least-squares results are presented and comparison has been made with ENDF/B-V and other evaluations.