The Measurement of Eta and Other Nuclear Properties of U²³³ and U²³⁵ in Critical Aqueous Solutions

The thermal value of eta for U²³³ and U²³⁵ has been determined in a series of experiments on unreflected homogeneous aqueous solutions of the two isotopes. These experiments also yield a value for the neutron age and the limiting concentrations of the fissile isotope in the aqueous solutions for infinite volumes. Auxiliary experiments, establishing limits of error, testing certain aspects of the theoretical model employed, and experimentally determining the parameters in the critical equation, have been performed. Experiments performed with 27-in.- and 48-in.-diam spheres, and 5-ft- and 9-ft-diam cylinders have yielded consistent values of eta. Measurements of the nonleakage probability in cylindrical geometry have given values consistent with those predicted by a two-group model in which the theoretical value of the age was used. Within the experimental error no differences were found in the ages of fission neutrons for U²³³ and U²³⁵. The average thermal values of eta determined are: for U²³³, 2.292 ± 0.015 and for U²³⁵, 2.076 ± 0.015. The 2200 meters/sec values are the same since the g-factors for eta are unity. The value of the neutron age to the indium resonance energy for U²³⁵ fission neutrons in water was found to be 25.6 ± 1.3 cm². The minimum U²³³ and U²³⁵ critical densities for these nitrate solutions were found to be 11.25 ± 0.10 gm/liter and 12.30 ± 0.10 gm/liter for U²³³ and U²³⁵, respectively.