Room 307, Gilman Hall, University of California

Room 307 is a small research laboratory in the attic of Gilman Hall, near the center of the University of California campus in Berkeley. In February 1941, researchers there first identified plutonium, element 94, a man-made element. Five co-workers shared in the discovery: Arthur Wall, Edwin MacMillan, Glenn Seaborg, Emilio Segre and J.W. Kennedy. Using a cyclotron, they bombarded uranium oxide with neutrons and produced the isotope that became far more important than any other. Plutonium can be used in nuclear fission for power generation and as an atomic explosive. The nomination states that without this discovery, neither the atomic explosives of 1945 nor later nuclear reactors would have been possible. Seaborg and MacMillan later shared a Nobel Prize for related work. Nothing from that period remains in the room, which has been refitted many times with newer equipment and still serves as a research laboratory. Its importance rests entirely on the events that took place inside. It was designated a National Historic Landmark in December 1965.