 In 1939 he became an instructor in chemistry at Berkeley , was promoted to assistant professor in 1941 and professor in 1945 . University of California , Berkeley , physicist Edwin McMillan led a team that discovered element 93 , which he named neptunium in 1940 . In November , he was persuaded to leave Berkeley temporarily to assist with urgent research in radar technology . Since Seaborg and his colleagues had perfected McMillan 's oxidation @-@ reduction technique for isolating neptunium , he asked McMillan for permission to continue the research and search for element 94 . McMillan agreed to the collaboration . Seaborg first reported alpha decay proportionate to only a fraction of the element 93 under observation . The first hypothesis for this alpha particle accumulation was contamination by uranium , which produces alpha @-@ decay particles ; analysis of alpha @-@ decay particles ruled this out . Seaborg then postulated that a distinct alpha @-@ producing element was being formed from element 93 . 
