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[am-uh-rish-ee-uh m] /ˌæm əˈrɪʃ i əm/
noun, Chemistry.
a transuranic element, one of the products of high-energy helium bombardment of uranium and plutonium. Symbol: Am; atomic number: 95.
Origin of americium
An Americanism dating back to 1945-50; Americ(a) + -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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British Dictionary definitions for americium


a white metallic transuranic element artificially produced from plutonium. It is used as an alpha-particle source. Symbol: Am; atomic no: 95; half-life of most stable isotope, 243Am: 7.4 × 10³ years; valency: 2,3,4,5, or 6; relative density: 13.67; melting pt: 1176°C; boiling pt: 2607°C (est)
Word Origin
C20: from America (because it was discovered at Berkeley, California) + -ium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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americium in Medicine

americium am·er·i·ci·um (ām'ə-rĭsh'ē-əm)
Symbol Am
A white metallic synthetic element of the actinide series; its longest-lived isotopes, Am 241 and Am 243, are used as radiation sources in research. Atomic number 95; specific gravity 13.7; valence 2, 3, 4, 5, 6.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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americium in Science
Symbol Am A synthetic, silvery-white, radioactive metallic element of the actinide series that is produced artificially by bombarding plutonium with neutrons. Americium is used as a source of alpha particles for smoke detectors and gamma rays for industrial gauges. Its most stable isotope has a half-life of 7,950 years. Atomic number 95; specific gravity 11.7; valence 3, 4, 5, 6. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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