Measurement of Average Cross Section for 233U(n, 2n)232U Reaction

Abstract

Isotopically pure 233U samples, with only 3 × l0−3 ppm232U content, were prepared by thermal neutron irradiation of thoria and subsequent chemical processing. The 233U sample thus obtained was reirradiated with a fission neutron spectrum in the core of the Kyoto University Reactor (KUR), and measurements were made of the fission spectrum average cross section for the 233U(n, 2n) 232U reaction. A value of 4.08±0.30 mb was obtained for this cross section, in agreement with the renormalized value of Halperin et al. within the limits of experimental error. In order to assess the energy dependent cross section from the value of this integral measurement, the 233U (n, 2n) cross section was calculated assuming a Maxwellian-type fission spectrum and adopting the energy dependent evaluated cross sections of ENDF/B-III and other authors. The values of the cross section thus determined were found to be about 32 to 91% larger than the measured cross section given above. The result of Pearlstein's calculation of the 2...