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neptunium

(nep to̵̅o̅′nē əm, -tyo̵̅o̅′-)

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noun

a silver-colored, radioactive, metallic chemical element, one of the actinides, produced by bombarding uranium atoms with neutrons: symbol, Np; at. no., 93

Origin: ModL < Neptunus, Neptune + -ium: so named by Edwin Mattison 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

See neptunium in American Heritage Dictionary 4

noun Symbol Np

A silvery, metallic, naturally radioactive element, atomic number 93, the first of the transuranium elements. Its longest-lived isotope is Np-237 with a half-life of 2.1 million years. Found in trace quantities in uranium ores, it is produced synthetically by nuclear reactions. See Table at element.

Origin:

Origin: After the planet Neptune (from the fact that it follows uranium in the periodic table)

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