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Atomic Number: 95
Atomic Symbol: Am
Atomic Weight: 243
Melting Point: 2,149 F (1,176 C)
Boiling Point: 3,652 F (2,011 C)
Word Origin: Americium was named after the continent of North America. Its name references its lighter lanthanide homologue, europium, which was named after Europe where it was discovered.
Discovery: Because americium is a synthetic transuranic element, its discovery was really a creation. It was made by Glenn Seaborg, Ralph James, Leon Morgan and Albert Ghiorso late in 1944 at the wartime metallurgical laboratory at the University of Chicago. It was made as the result of successive neutron capture reactions by plutonium isotopes in a nuclear reactor.
Americium was the fourth synthetic transuranic element to be discovered. Unlike previously discovered transuranic elements, americium chemically behaved like the lanthanide series of elements. This behavior, and the similar behavior of newly discovered element curium, prompted Seaborg to radically revise the periodic table and create the actinide series. [Related: How Are the Elements Grouped?]
The initial discovery was classified as secret as part of the Manhattan Project during World War II, but was later declassified. Seaborg announced its discovery on the U.S. children’s radio show, "The Quiz Kids," five days before his planned presentation at an American Chemical Society in November 1945. One of the young listeners asked whether any new transuranium element beside plutonium and neptunium had been discovered, and Seaborg responded with the announcement.
Properties of americium
Americium is highly radioactive. Freshly prepared americium metal gives off a white, somewhat silvery luster. It tarnishes slowly in dry air at room temperature. Americium is more malleable than uranium or neptunium. Americium has numerous compounds. In solutions, americium has oxidation states III, IV, V, and VI. In carbonate solutions, americium can coexist in all four oxidation states simultaneously. It is only the second element, after plutonium, to do this.
Like all highly radioactive elements, americium and its compounds must be handled carefully in a laboratory under special containment conditions. When gram quantities of 241Am are handled, the intense gamma activity makes exposure a serious problem. [See Periodic Table of the Elements]
Sources of americium
Americium is made synthetically. The first substantial amounts of metallic americium were not prepared until 1951 through reduction of americium(III) fluoride with barium metal in high vacuum at 1,100 C (2,012 F), producing up to 200 milligrams. Now americium can be made in kilogram quantities.
Uses of americium
241Am has proven to have many uses, including as an ionization source in smoke detectors. 241Am has been used as a portable source of gamma-rays and alpha particles. In this way, it can be used in indirect analysis of materials in radiography and X-ray fluorescence spectroscopy. It can also be used to gauge glass thickness and produce flat glass.
Isotopes of americium
Americium currently has 19 known isotopes and 8 nuclear isomers. The half-lives for most isotopes and isomers range from 0.64 microseconds for 245Am to 50.8 hours for 240Am. 241Am and 243Am are the longest living with half-lives of 432.2 and 7,370 years, respectively. They are alpha-emitters and are now available in high-purity kilogram quantities. The nuclear isomer 242Am has a half-life of 141 years. Like most other actinides, the isotopes of americium with odd numbers of neutrons have relatively high rate of nuclear fission and low critical mass.
(Source: Jefferson Lab)