English: A view of the east (to the left) and north faces of Argonne's uranium-graphite nuclear reactor, CP-2. The reactor, originally constructed at the University of Chicago's West Stands and titled CP-1, was dismantled in early 1943 and reassembled at the Palos Park Site away from the city congestion. At that time, the concrete radiation shield was added. The small laboratory on the top of the reactor, referred to as "the penthouse," was constructed to house experiments on the properties of neutrons emitted from the reactor.