Transuranic element
From Tardis Wiki, the free Doctor Who reference
A transuranic element was any element with an atomic number higher than Uranium. These included Neptunium and Plutonium. (AUDIO: Power Play)
The First Doctor suggested that the people of Arkhaven may have mastered the use of stable transuranic elements, which would have allowed them to launch a spacecraft from the centre of their city without worrying about the pollution it would cause. (PROSE: City at World's End)
