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).] |
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