Fission spectrum averaged cross section for the 232Th(n, f) reaction

Abstract

Fission spectrum averaged cross sections for the 232Th(n, f) reaction were measured relative to the average cross section of 102 mb for the 58Ni(n, p) 58Co reaction, (1) at the beam port E-3 of the Kyoto University Reactor (KUR) where the fast neutron spectrum had previously been confirmed to be equivalent to that of fission neutrons, and (2) with a fission plate installed at the thermal neutron facility of KUR. In the first experiment, a fission chamber composed of a thorium film and a silicon detector was used and the measured value was 77.4 ± 3.7 mb. Anisotropic effect in the fragment angular distributions was investigated by a Monte Carlo calculation. In the second experiment with the fission plate, induced-activities of 140Ba in the thorium foil were measured with a Ge(Li) detector, and the result was 78.1 ± 3.9 mb. These data are in good agreement with each other. Most of the average cross sections calculated by several researchers are generally around 70 mb, which is smaller by about 10% than the results of the integral measurements. The Fabry's value is about 7% larger than those of the author's.