McMillan, Edwin Mattison (1907-1991), an American nuclear physicist, discovered the element neptunium. He made the discovery jointly with his colleague Philip Abelson in 1940. The new element was the first discovered of the transuranium elements, elements heavier than uranium, the heaviest natural element (see Transuranium element). McMillan shared the 1951 Nobel Prize for chemistry with Glenn T. Seaborg for their discovery of the transuranium elements (see Seaborg, Glenn Theodore). McMillan and Seaborg were part of a team at the University of California at Berkeley that discovered the elements plutonium, americium, curium, berkelium, and californium.