A Direct Comparison of Some Nuclear Properties of U-233 and U-235

Abstract

Nuclear properties of U233 and U235 are compared using data obtained in a series of critical experiments. Aqueous solutions of uranyl oxyfluoride containing uranium enriched to about 90% in each of the two isotopes have been made critical in water-reflected spherical reactors having diameters of 26.4 and 32.0 cm. Assuming the reported nuclear constants for U235 are reliably known and assuming equality of the neutron leakage spectra of U233 and U235 for the same water-reflected critical sphere, the value of η(U233) at 0.026 ev was determined to be 2.31 ± 0.03. The critical masses for the two isotopes in these systems have been measured over the temperature range from 20°C to 100°C; corresponding values of the reactivity temperature coefficient are reported. Delayed neutron yields for the two isotopes were compared by noting the periods resulting from the withdrawal of a boron poison from the critical spheres. It is shown that the yield from U233 is about one-third that from U235, in agreement with other determinations.