Integral Reaction Rate Determinations—Part II: Fission Rate Measurements

Integral fission rates were measured for ²³²Th, ²³³U, ²³⁵U, ²³⁶U, ²³⁸U, ²³⁷Np, ²³⁹Pu, ²⁴⁸Pu, ²⁴¹Pu, ²⁴¹Am, ^232mAm, and ²⁴³Am in four tailored epicadmium neutron spectra. The fission rates were determined by counting fission fragment tracks in solid-state track recorders. The measured and calculated fission rates differed by <7% for ²³²Th, ²³³U, ²³⁸U, ²³⁶U, and ²³⁷Np in each spectrum. There is evidence that the ²³²Th, ²³⁸U, and ²³⁷Np differential data need slight normalization corrections. Plutonium-239, ²⁴⁰Pu, ²⁴¹ Pu, ²⁴¹ Am, ^242mAm, and ²⁴³Am each exhibited larger deviations of measured from calculated activities than the lighter nuclides. The magnitude of the deviations varied from one spectrum to another for some materials, indicating the possibility of not only magnitude but also shape uncertain-ties for the differential cross sections.