Measurement of the Ratios of Capture and Fission Neutron Cross Sections of ²³⁵U, ²³⁸U, and ²³⁹Pu at 130 to 1400 keV

The ratios σγ(²³⁸U)/σ/(²³⁵U), σγ(²³⁸U)/σγ(²³⁹Pu), and σ_f (²³⁹Pu)/σ_f (²³⁵U) have been measured in the energy range 130 to 1400 keV. The activation technique was used to determine the capture rate in ²³⁸U. The 278 keV γ ray emitted in the decay of ²³⁹Np was detected by means of a Ge(Li) detector. The counting efficiencies have been absolutely determined for the measurement of σγ(²³⁸U)/σ_f(²³⁹Pu). For the determination of the ratio σγ(²³⁸U)/σ_f(²³⁵U) the counting efficiencies have been eliminated by a measurement of the ratio at thermal-neutron energies. The ratio σ_f(²³⁹Pu)/σ_f(²³⁵U) has been measured in a back-to-back gas scintillation counter using the time-of-flight method for background suppression. The measurements resulted in an overdetermination of two unknown quantities by three measured values. The fitted values derived from the collective results were in good agreement with the individual measured ratios.