nep·tu·ni·um (n p-t  n - m, -ty-)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 Table at element. [After the planet Neptune (from the fact that it follows uranium in the periodic table).] |
neptunium [nɛpˈtjuːnɪəm]
n
(Chemistry / 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.)
[from Neptune2, the planet beyond Uranus, because neptunium is the element beyond uranium in the periodic table]
| neptunium (np-tn-m) 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 byproduct of plutonium production. Its longest-lived isotope is Np 237 with a half-life of 2.1 million years. Atomic number 93. See Periodic Table. |
ThesaurusLegend: Synonyms Related Words Antonyms
| Noun | 1. |  neptunium - a radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutoniummetal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc. |
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