U233Fission Cross Section Measured Using a Nuclear Explosion in Space

A high-altitude nuclear explosion in 1962 was used as a neutron source in an experiment to measure the fission cross section of ${\mathrm{U}}^{233}$ relative to ${\mathrm{U}}^{235}$ in the 30-eV to 5-MeV energy region. Fission data were telemetered to the ground station at Kauai, Hawaii from sounding rockets carrying the fission counters which were near their apogee at the time the nuclear explosion occurred over Johnston Island. The flight path for the neutron time-of-flight experiment was 1280 km. The ${\mathrm{U}}^{233}$ fission-cross-section results indicated average values about 20% lower in the 2-MeV energy region and about 30-40% higher in the 30-500-eV energy region than the average of previously obtained values. The results also fill the gap in ${\mathrm{U}}^{233}$ fission-cross-section data which existed between previous high-energy Van de Graaff and low-energy time-of-flight measurements in the 1-20-keV region.