Epithermal Measurements of Capture and Fission Resonance Integrals in ²³⁵U, ²³³U, ²³⁹Pu, and ²⁴¹Pu

The resonance integrals for capture and fission and their ratios, a, have been measured for ²³³U, ²³⁵U, ²³⁹Pu, and ²⁴¹Pu. Small samples of high isotopic enrichment were irradiated in a water channel of a swimming pool reactor. The number of captures was determined by mass spectrometry and the number of fissions was determined by ¹³⁷Cs analysis. A combination of cadmium and rhodium neutron filters was used to provide effective cutoff energies in the 2- to 4-eV range. The measured values of a above 3.0 eV are 0.148 ± 0.006, 0.615 ± 0.019, 0.723 ± 0.044, and 0.285 ± 0.015 for ²³³U, ²³⁵U, ²³⁹Pu, and ²⁴¹Pu, respectively. The corresponding values calculated from ENDF/B cross sections are 0.162, 0.608, 0.650, and 0.212.