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Americium is an element with atomic number 95 and atomic symbol Am. It was named for the Americas, by analogy with Europium, which was named for Europe. Its atomic weight is 243. It has a whitish, silvery color.
Americium is one of the Actinide or Actinoid group of elements in the Periodic Table of Elements. The Actinides, along with the Lanthanides, are classed as Inner Transition Elements among the Metals.
Americium, a radioactive metal, was isolated by Glenn T. Seaborg, who later won a Nobel Prize in Chemistry for his discoveries concerning the transuranium elements, in 1944–1945. Americium was the third of the ten elements that Seaborg had a part in discovering.
Americium had a role in Seaborg’s conceptual work as well. The actinide series was proposed by Seaborg, and his conception of this group arose from the difficulty he experienced in isolating americium and curium, the two elements he discovered while at the University of Chicago. The unexpected problem led him to theorize that these elements differed from transition metals and to propose a new conception of the periodic table, which was first published in 1945.
Americium is created by using neurons to bombard plutonium. Only a few pounds are produced each year. It is confined to laboratories because its high level of alpha radiation renders it very dangerous. Its alpha radiation is around three times greater than the alpha radiation of radium, and it emits quite a bit of gamma radiation as well.
Americium is used as a gauge in the glass industry, commercial smoke detectors, and as a neutron source when combined with other elements. Due to its role in smoke detectors, it is present in far more homes than any of the other synthetic elements. Its gamma ray emissions gave it a role in radiology; although no longer used in this application today, it was, at one time, used in the diagnosis of thyroid function.