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n. 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 Periodic Table.
[After the planet Neptune (from the fact that it follows uranium in the periodic table).]
(Elements & Compounds) 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)
[C20: from Neptune2, the planet beyond Uranus, because neptunium is the element beyond uranium in the periodic table]
nep•tu•ni•um(nɛpˈtu ni əm, -ˈtyu-)
a short-lived radioactive transuranic element produced in nuclear reactors by the neutron bombardment of U-238. Symbol: Np; at. no.: 93; at. wt.: 237.
Symbol Np A silvery, radioactive metallic element of the actinide series. It occurs naturally in minute amounts in uranium ores and is produced artificially as a by-product of plutonium production. The most stable isotope of neptunium has a half-life of 2.1 million years. Atomic number 93. See Periodic Table.
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|Noun||1.||neptunium - a radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutonium|