| The American Heritage® Dictionary of the English Language: Fourth Edition. 2000. |
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| neptunium |
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| SYLLABICATION: | nep·tu·ni·um |
| PRONUNCIATION: |  n p-t  n - m, -ty- |
| NOUN: | 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. | | ETYMOLOGY: | After the planet Neptune (from the fact that it follows uranium in the periodic table).
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| The American Heritage® Dictionary of the English Language, Fourth Edition. Copyright © 2000 by Houghton Mifflin Company. Published by the Houghton Mifflin Company. All rights reserved. |
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