The first synthetic element

Fermi, Segrè and the rest of the Boys took the idea one step further by bombarding a sample of uranium — element 92, the heaviest known element at that time — with an improvised neutron beam. In 1939, Berkeley researcher Edwin McMillan approached Segrè about an unusual atom that he’d discovered in the cyclotron, which he believed to be a new element. But arguably the greatest discovery remains technetium, and the metastable isotope of the element that Segrè discovered with Seaborg.

Source: www.nature.com