- a radioactive silver-white metallic element that glows blue in the dark, resembling the rare earths in chemical behavior and valence. Symbol: Ac; atomic number: 89; atomic weight: 227.
- a radioactive element of the actinide series, occurring as a decay product of uranium. It is used as an alpha-particle source and in neutron production. Symbol: Ac; atomic no: 89; half-life of most stable isotope, 227 Ac: 21.6 years; relative density: 10.07; melting pt: 1051°C; boiling pt: 3200 ± 300°C
radioactive element discovered in 1899, from Greek actin-, comb. form of aktis (genitive aktinos) “ray, radiance” (see actino-) + chemical suffix -ium.
n. Symbol Ac
- A radioactive element found in uranium ores. Its longest lived isotope is Ac 227 with a half-life of 21.6 years. Atomic number 89.
- A silvery-white, highly radioactive metallic element of the actinide series that is found in uranium ores. It is about 150 times more radioactive than radium and is used as a source of alpha rays and neutrons. Its most stable isotope has a half-life of about 22 years. Atomic number 89; melting point 1,050°C (1,922°F); boiling point (estimated) 3,200°C (5,792°F); specific gravity (calculated) 10.07; valence 3. See Periodic Table.