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polonium po·lo·ni·um (pə-lō'nē-əm)
A naturally radioactive metallic element, occurring in minute quantities in uranium ores; its most readily available isotope is Po 210, with a half-life of 138.39 days. Atomic number 84; melting point 254°C; boiling point 962°C; specific gravity 9.32; valence 2, 4.
A very rare, naturally radioactive, silvery-gray or black metalloid element. It is produced in extremely small amounts by the radioactive decay of radium or the bombardment of bismuth or lead with neutrons. Atomic number 84; melting point 254°C; boiling point 962°C; specific gravity 9.32; valence 2, 4. See Periodic Table.
a radioactive, silvery-gray or black metallic element of the oxygen family (Group VIa in the periodic table). The first element to be discovered by radiochemical analysis, polonium was discovered in 1898 by Pierre and Marie Curie, who were investigating the radioactivity of a certain pitchblende, a uranium ore. Polonium is a very rare element (its abundance in the Earth's crust is about one part in 1015) that occurs in nature as a radioactive decay product of uranium, thorium, and actinium. The half-lives of its isotopes range from a fraction of a second up to 103 years; the most common natural isotope of polonium, polonium-210, has a half-life of 138.4 days.