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americium am·er·i·ci·um (ām'ə-rĭsh'ē-əm)
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.
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.