Neptunium is a chemical element with the symbol Np and atomic number 93. It is a silvery, radioactive metal that belongs to the actinide series of the periodic table. Neptunium is notable for being the first transuranium element, meaning it was the first element discovered that has an atomic number greater than that of uranium (92). Neptunium was discovered in 1940 by Edwin McMillan and Philip H.
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