Radioactive metal. Presumed to be a reactive meal akin to Neodymium and Praseodymium m.p. ~1080 ºC; ~1976 ºF b.p. 2460(?) ºC; 4460(?) ºF density unknown	memory peg
	1945 Charles D. Coryell, with Jack A. Marinsky and Lawrence E. Glendenin, United States
	Προμηθευς (Prometheus), mythological figure (Greek)

Promethium was the last of the rare-earths family elements to be discovered.
In 1902 the Czech chemist Bohuslav Brauner (1855-1935) improved Mendeleyev's period chart by extending it downward after Lanthanum. He predicted the existence of an element in between Neodymium and Samarium.

Henry Moseley's study of X-ray spectra confirmed in 1913-14 that an element was missing at atomic #61. A search of minerals containing adjoining elements brought claims of discovery.

• 1924, the Italian chemist Luigi Rolla (1882-1960) with the young graduate Lorenzo Fernandes (1902-1977) in Florence, Italy, claimed to have discovered element #61. In 1924 he had sent a sealed envelope to the Royal Accademia dei Lincei in Rome containing his results on identification of element 61. He named it Florentium (Florenzio), symbol Fr (not Fl as it is often reported in scietific journals), after Florence in Italy.

• 1926, B. Smith Hopkins (1873-1952) and his coworkers Len Yntema and a Canadian graduate student named Harris of the University of Illinois-Urbana (note) reported its discovery and suggested the name Illinium, (symbol Il) after the American state of Illinois. But other chemists, as the rare-earth specialist Wilhelm Prandtl (1878-1956) and Walter Noddack and Ida Tacke Noddack (1896-1979), discovers of Rhenium, were unable to confirm this new element.

• 1938: Laurence L. Quill (1901-1989) and colleagues used the new Ohio State cyclotron to bombard Neodymium and Samarium with various projectiles. A number of radioactive isotopes were produced, presumably including one due to element #61 for which they proposed the name Cyclonium.

• 1942: Element #61 probably made by Chien Shiung Wu, Emilio G. Segrè et Hans Albrecht Bethe during a bombardement of Neodymium and Praseodymium with neutrons. Chemical proof was lacking because of the difficulty in separating the rare earths from each other at that time.

Isolation and identification of element #61 was finally made in 1945 (confirmed 1947) by Charles D. Coryell (1912-1971) and his associates Jacob (Jack) A. Marinsky (b. 1918) and Lawrence E. Glendenin (1918-?), together with Harold G. Richter. They worked for the Manhattan Project at Oak Ridge, Tennessee, where scientists had to create the fuel for an atomic bomb. They identified ¹⁴⁷61 in the by-products uranium fission. Element #61 emitted beta rays with a 3.7-year half life. ¹⁴⁷61 was confirmed by mass spectrograph. The most stable isotope currently known has a half-life of 25 years, too short to be in any of the minerals investigated in the 1920s.

Grace Mary Coryell suggested the name Prometheum after Προμηθευς [Prometheus], who according to Greek mythology stole fire from heaven and gave it to humans. Since Promethium does not exist except in fission products, it was named for the courage and pain needed to synthesize new elements. In 1949 the International Union of Chemistry adopted the spelling Promethium.

Further reading:

• Mary Elvira Weeks, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 835-837.
• M. Costa, M. Fontani, P. Papini, & P. Manzelli, "Storia dell'elemento 61", Memorie di Scienze Fisiche e Naturali. Accademia delle Scienze detta dei XL, 431, vol. XXI, serie V, parte II, tomo II, (1997) (In Italian, history of element 61, with a resumé in English).
• M. Fontani, M. Costa, P. Manzelli, "Un elemento macato: il Florenzio." Il Chimico Italiano no. 1, 32, (1997).