nep·tu·ni·um /nɛpˈtuniəm, ˈtju-/
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 nep·tu·ni·um /nɛpˈt(j)unɪəm/ 名詞
 (abbr.np)拿


 neptunium
      n : a radioactive transuranic metallic element; found in trace
          amounts in uranium ores; a by-product of the production
          of plutonium [syn: Np, atomic number 93]


 neptunium
 Symbol: Np
 Atomic number: 93
 Atomic weight: (237)
 Radioactive metallic transuranic element, belongs to the actinoids.
 Np-237, the most stable isotope, has a half-life of 2.2*10^6 years and is
 a by product of nuclear reactors. The other known isotopes have mass
 numbers 229 through 236, and 238 through 241. Np-236 has a half-life of
 5*10^3 years. First produced by Edwin M. McMillan and P.H. Abelson in
 1940.