Fission cross-sections of U and Pu averaged over Cf neutron spectrum

A series of measurements have been carried out to derive values for the spectrum-averaged fission cross-section of ²³⁵U and ²³⁹Pu for ²⁵²Cf fission neutrons. Two nearly identical target foils were mounted on either side of a Cf source (10⁷ neutron/sec) in a compensated beam geometry. Fission fragments passing through limited solid angle apertures were recorded from each foil by solid-state track-etch techniques. The Cf neutron source strength was calibrated in manganese bath relative to the standard source NBS-II. Values of 1.215 ± 0.022 barn for ²³⁵U and 1.790 ± 0.041 barn for ²³⁹Pu were obtained for the fission cross-sections, corresponding to a ratio value of 1.473 ± 0.041.