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A radioactive element found in uranium ores, used in equilibrium with its decay products as a source of alpha rays; such as, pitchblende (a mineral consisting of uranium oxide and trace amounts of radium and thorium and polonium and lead and helium; uraninite in massive form is called pitchblende which is the chief uranium ore).
It possesses no stable isotopes and exists in nature only as a disintegration product of uranium and thorium.
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.
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