Measurement of the capture-to-fission cross section ratios of 235U and 239Pu with a new technique

The ratio of capture to fission cross section, α, has been measured for 235U and 239Pu in the neutron energy range from 8 to 60 keV. A pulsed neutron beam from a 7Li Van de Graaff source was used. The absorption was found by a comparison of the scattered neutrons from the fissile sample with those from a non-absorbing lead sample. The fast fission neutrons were simultaneously detected with an organic liquid scintillator. The normalization of the α (239Pu) data was slightly changed with respect to the values reported earlier in the light of recent evaluations.