| 释义 |
WordReference Random House Unabridged Dictionary of American English © 2024nep•tu•ni•um (nep to̅o̅′nē əm, -tyo̅o̅′-),USA pronunciation n. [Chem., Physics.]- Physics, Chemistrya transuranic element produced in nuclear reactors by the neutron bombardment of U-238: decays rapidly to plutonium and then to U-235. Symbol: Np;
at. no.: 93.
Collins Concise English Dictionary © HarperCollins Publishers:: neptunium /nɛpˈtjuːnɪəm/ n - 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)
Etymology: 20th Century: from Neptune², the planet beyond Uranus, because neptunium is the element beyond uranium in the periodic table |