| The American Heritage® Dictionary of the English Language: Fourth Edition. 2000. |
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| actinium |
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| SYLLABICATION: | ac·tin·i·um |
| PRONUNCIATION: |   k-t n  - m |
| NOUN: | Symbol Ac1 A radioactive element found in uranium ores, used in equilibrium with its decay products as a source of alpha rays. Its longest lived isotope is Ac 227 with a half-life of 21.6 years. Atomic number 89; melting point 1,050°C; boiling point (estimated) 3,200°C; specific gravity (calculated) 10.07; valence 3. See table at element. | | ETYMOLOGY: | From Greek akt s, aktn-, ray (from its radioactivity). See actino–.
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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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