Polonium

Polonium, symbol Po, rare, radioactive metallic element. Polonium is in group 16 (or VIa) of the periodic table (see Periodic Law). Its atomic number is 84.

The first element to be discovered by means of its radioactivity, polonium was found in pitchblende in 1898 by the French chemist Marie Curie, who named it for her native country, Poland. Polonium is one of the elements in the uranium-radium series of radioactive decay, the first member of which is uranium-238. Polonium is extremely rare in nature. Trace amounts of the element occur in radium-containing ores. Polonium 210 (also called radium-F), the most common naturally occurring isotope, has a half-life of 138 days. Many other isotopes of the element have been synthesized. Polonium melts at about 254°C (about 489°F), boils at about 962°C (about 1764°F), and has a specific gravity of 9.3.

Because most polonium isotopes disintegrate by emitting large numbers of high-energy alpha particles, the element is a good source of alpha radiation. Polonium is used in nuclear research with elements such as beryllium that emit neutrons when bombarded by alpha particles. In printing and photography equipment, polonium has been used in devices that ionize the air to eliminate accumulation of electrostatic charges. The element’s extreme radioactivity makes exposure to even tiny amounts of it extremely dangerous.