A cadmium-aluminum shield for the V.P.I. subcritical reactor was designed and constructed. Aluminum provides structural strength. Suitable access to fuel and experimental facilities was provided. Experimentally it was determined that the shield is opaque to an influx of thermal neutrons. This is manifested by a depression in neutron density near the boundaries of the pile when the shielded and unshielded region counting rates are compared. The natural-uranium slugs and the highly radioactive source are padlocked within the shield. The assembly is also protected from contamination. Practically no additional biological protection is afforded by the shield due to the neutron-gamma reaction in cadmium. / Master of Science