The good people at Oak Ridge National Laboratory just shared this picture with me... Too late for our Promethium video but thought I'd share it here.
Caption: While working at the Graphite Reactor, Jacob Marinsky and Lawrence Glendenin produce the rare-earth element 61, promethium. They do so through uranium fission and by bombarding neodymium with neutrons from fissioning uranium in the reactor. Promethium-147 is later used in nuclear-powered batteries for instruments in guided missiles. Label marked Prepared At Oak Ridge National Laboratory by G.W. Parker, J.W. Ruch, and J. Reed.