The Resonance Fission Integrals of U²³⁵, Pu²³⁹, and Pu²⁴¹

The resonance fission integrals of U²³⁵, Pu²³⁹, and Pu²⁴¹ have been measured relative to the gold resonance capture integral by the cadmium ratio method. The cadmium ratios were measured in a reactor at a position where the epicadmium flux spectrum was closely 1/E except for a peak above 25 kev. A small spectrum correction was made for this flux peak to infer the fission integral over a pure 1/E spectrum using a calculated epicadmium flux spectrum. The resonance integrals obtained were, with a 0.5-ev cutoff energy, 274 ± 11b, 327 ± 22b, and 557 ± 33b for U²³⁵, Pu²³⁹, and Pu²⁴¹, respectively.