Parameters of the 1.056-eV Resonance in ²⁴⁰Pu and the 2200 m/s Neutron Total Cross Sections of ²³⁵U, ²³⁹Pu, and ²⁴⁰Pu

The Bayesian method was applied to the simultaneous fitting of neutron transmission measurements on five thin and two thick samples of ²⁴⁰Pu to obtain the parameters of the very large resonance near 1 eV. The results of the analysis are E₀ = 1.0564 ± 0.0006 Γγ, = 30.3 ± 0.3 meV, and _Γn = 2.45 ± 0.02 meV. Some evidence in the data of a small deviation from the usual “weak binding” model for Doppler broadening of the theoretical resonance shape is presented. Transmission measurements on samples of ²³⁵U, ²³⁹Pu, and ²⁴⁰Pu also were made over the thermal energy region and their neutron total cross sections were derived. Fits of the form A + B to the cross-section data in the interval from 0.02 to 0.03 eV resulted in the values 690 ± 5, 1025 ± 6, and 284 ± 2 b for the 2200 m/s total cross sections of ²³⁵U, ²³⁹Pu, and ²⁴⁰Pu, respectively.