The Fission Cross Section of Plutonium-240 Relative to Uranium-235 from 0.35 to 9.6 MeV

The ²⁴⁰Pu-to-²³⁵U fission cross-section ratio has been measured at 55 discrete energies between thresh-old and ∼10 MeV using the ⁷Li(p,n)⁷Be and D(d,n)³He reactions as neutron sources. The sample masses were measured by (a) calculated specific activities and low geometry alpha counting, (b) by mass spectrographic isotopic dilution analyses, and (c) by comparing the relative thermal fission rates of one of the ²³⁵U samples with ²⁴⁰Pu samples containing ∼9% ²³⁹Pu.