Beyond Uranium, Ca. 1890–1950

Abstract

The transuranic elements at the end of the periodic table have since the 1960s been known as superheavy elements. Until 1939 no element heavier than uranium was known and yet there was in the earlier period considerable interest in the possible existence of such elements. The interest was in part of a speculative nature and in part based on calculations of the electron structure of heavy elements. After all, why should uranium be the heaviest element in nature? Although transuranic elements were “known” theoretically in the 1920s, it was only with the development of nuclear physics and technology in the following decade that the first of these elements—neptunium and plutonium—were actually produced. By 1951 six transuranic elements had been added to the periodic table, all of them by an innovative group of Californian nuclear scientists.