n. Symbol Ac
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 21.77 years. Atomic number 89; melting point 1,050°C; boiling point 3,198°C; specific gravity (calculated) 10.07; valence 3. See Periodic Table.
[From Greek aktīs, aktīn-, ray (from its radioactivity); see nekw-t- in the Appendix of Indo-European roots.]
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