Report containing experiments conducted at the Oak Ridge National Laboratory's Critical Experiments Facility. These experiments involved "determining the critical parameters of the assembly with varying amounts of neutron absorber in the D20 reflector, measuring the relative neutron flux distribution for various conditions of reflector poison and fissile solution concentration, determining the ratio of the absolute thermal-neutron flux in the center of the assembly to the power in the fissile solution , and determining the effect on reactivity of reducing the hydrogen density in the central region of the assembly" (p. 1).