| The American Heritage® Dictionary of the English Language: Fourth Edition. 2000. |
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| protactinium |
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| SYLLABICATION: | pro·tac·tin·i·um |
| PRONUNCIATION: |  pr  t k-t n  - m |
| NOUN: | Symbol Pa A rare, extremely toxic, radioactive element chemically similar to uranium, having 13 known isotopes, the most common of which is protactinium 231 with a half-life of 32,480 years. Atomic number 91; melting point 1,230°C; specific gravity 15.37; valence 4, 5. See table at element. | | ETYMOLOGY: | prot(o)– + actinium (so called because it decays into actinium).
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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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