a silvery metallic transuranic element synthesized in the production of plutonium and occurring in trace amounts in uranium ores. Symbol: Np; atomic no: 93; half-life of most stable isotope, 237Np: 2.14 × 106 years; valency: 3, 4, 5, or 6; relative density: 20.25; melting pt: 639±1°C; boiling pt: 3902°C (est)
Word origin
C20: from Neptune2, the planet beyond Uranus, because neptunium is the element beyond uranium in theperiodic table
neptunium in American English
(nɛpˈtuniəm; nɛpˈtjuniəm)
US
noun
a silver-colored, radioactive, metallic chemical element, one of the actinides, produced by bombarding uranium atoms with neutrons: symbol, Np; at. no., 93
Word origin
ModL < Neptunus, Neptune + -ium: so named by McMillan & P. Abelson (1913-2004), U.S. physicists, because its at. no. is next after uranium's,as the planet Neptune is next beyond Uranus