Polonium
. Polonium, symbol Po, rare, radioactive metallic element. Polonium is in group 16 (or VIa) of the periodic table . 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 occurs in radium-containing ores and is found in isotopic forms with mass numbers ranging from 192 to 218. Polonium 209 (also called radium-F), the only naturally occurring isotope, has a half-life of 138 days. Polonium melts at about 254° C (about 489° F), boils at about 962° C (about 1764° F), and has a specific gravity of 9.4. Because most polonium isotopes disintegrate by emitting alpha particles , the element is a good source of pure alpha radiation. It is also used in nuclear research with elements such as beryllium that e