What event did Henry Moore’s Atom Piece at the University of Chicago commemorate?

Henry Moore’s Atom Piece, located at the University of Chicago, commemorates the first self-sustaining nuclear chain reaction.1

This historic event took place on December 2, 1942, when a team of physicists led by Enrico Fermi achieved the reaction beneath the football stands at the university as part of the Manhattan Project. While the sculpture features a distinct mushroom-cloud formation at its top, it also reflects Moore's broader exploration of large-scale abstract forms during the 1960s.21