Interior of an americium-based smoke detector
13 January 2023
(Updated 22 May 2023: added 19 April 1946 Science reference)
Americium, element 95, was first produced by a team led by chemist Glenn Seaborg in 1944 at the University of California, Berkeley and identified by the Manhattan Project’s Metallurgical Laboratory (now Argonne National Lab), located at the University of Chicago. It was the fourth transuranic element to be discovered, after neptunium, plutonium, and curium. Announcement of the discovery was delayed until November 1945 due to wartime security, and the first public mention of the new element’s name was on 10 April 1946. From an Associated Press report of that date:
Seaborg, who last fall announced the existence of the new elements 95 and 96—radioactive elements that somewhat resemble the so-called rare earths—today proposed formal names for them.
He suggested that element 95 be called “Americium,” with the symbol “Am” in honor of the Americans [sic]; and that the element 96 be called “curium,” with the symbol “Cm” in honor of Pierre and Marie Curie, who obtained radium from pitchblende.
The journal Science reported on the discovery on 19 April 1946, including a prediction by some chemists on how the name would be pronounced and spelled:
The two new elements, 95 and 96, were given names by Glenn T. Seaborg at the meeting of the Physical and Inorganic Division of the American Chemical Society meeting at Atlantic City on 10 April. He recommended that 95 be called “americium” with the symbol, Am, after the Americas, and that 96 be called “curium” after the Curies. Dr. Seaborg also recommended that the soft “c” be used in the pronunciation of americium, but some of his hearers thought that it would not be long until the second “i” will be dropped and the pronunciation changed, in the United States at least, following the history of aluminium.
The prediction turned out to be wrong.
Seaborg gave a fuller account of the reasons for the name in a 25 October 1946 article in the journal Science. Seaborg explains the name did not arise (solely) out of patriotic fervor, but the element was named for all of the Americas and had a justification in its position on the periodic table similar to that of europium.
Elements 95 and 96 should, of course, have names, and these investigators have proposed the following in which these “actinide” elements (see [periodic table] below) are given names by analogy with the corresponding members of the “lanthanide” earths. They have suggested for element 95, with its six 5f electrons, the name “americium” (symbol, Am); thus, this element would be named after the Americas, or New World, by analogy with europium, with its six 4f electrons, which was named after Europe. For element 96, containing seven 5f electrons, they have suggested “curium” (symbol, Cm), after Pierre and Marie Curie, historical leading investigators in the field of radioactivity; this is by analogy with gadolinium, containing seven 4f electrons, which recalls Gadolin, the great investigator of the rare earths.
Americium is widely used in smoke detectors.
Sources:
Associated Press. “World A-Energy Controls Declared Necessary: Scientist Says Alternative is Non-Commercial Use of Power.” Columbus Evening Dispatch (Ohio), 10 April 1946, 2-A. Readex: America’s Historical Newspapers.
Oxford English Dictionary, third edition, June 2008, s.v. americium, n.
“U.S. News and Notes.” Science, 103.2677, 19 April 1946, 480–82 at 481. DOI: 10.1126/science.103.2677.480.
Seaborg, Glenn T. “The Transuranium Elements.” Science, 104.2704, 25 October 1946, 384–85. JSTOR.
Seaborg, Glenn T., Ralph A. James, and Leon O. Morgan. “The New Element Americium (Atomic Number 95).” Oak Ridge, Tennessee: United States Atomic Energy Commission, AECD-2185, January 1948. US Department of Energy: Office of Scientific and Technical Information.
Image credit: Mark D., 2009. Wikimedia Commons. Licensed under a Creative Commons Attribution-Share Alike 2.0 Generic license.