Definition of "actinium" []

• 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. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "In collaboration with Rona, she applied her method to the study of the ranges of alpha particles emitted from actinium and polonium. 6 7"
• "Hahn's radiothorium and actinium salts also followed him to Emil Fischer's laboratory in Berlin. 30"
• "In France, Debierne had discovered actinium and Giesel claimed to have found a different element, emanium."