In 1963 Moore was invited by the University of Chicago to make a sculpture commemorating the first controlled nuclear chain reaction, which had been conducted at the university in 1942. Nuclear Energy, which is shown in the photograph above, was unveiled in 1967. This sculpture is a working model for Nuclear Energy. Moore intended it to suggest ‘a contained power and force’ appropriate to the subject. Its shape suggests a human skull and a mushroom cloud. In 1987, the city of Hiroshima, which had been destroyed by a nuclear bomb in 1945, purchased one of the seven casts.