Polonium
Polonium, a radioactive, metallic chemical element. Polonium is part of the radioactive decay series through which uranium 238 is converted to lead. Polonium was discovered in pitchblende by Pierre and Marie Curie in 1898 and was named for Poland, her native country. Polonium was the first element discovered by its radioactivity. It is used in research laboratories as a source of alpha particles, a type of nuclear radiation.
Symbol: Po. Atomic number: 84. Atomic weight of most stable isotope: 209. Specific gravity: 9.3. Melting point: 489 F. (254 C.), Boiling point: 1764 F. (962 C.). Polonium has 27 isotopes Po-192 through Po-218)—more than any other element. It belongs to Group VI-A of the Periodic Table and may have a valence of + 2 or 4.