Polonium

Gregor Mendeleev, who is sometimes called the “father of the periodic table,” predicted an element with polonium’s qualities in 1891. His pioneering periodic table had made it possible to predict the existence of elements that hadn’t yet been discovered—a kind of chemical crystal ball!

Seven years later, in 1898, French chemists Pierre and Marie Curie were investigating pitchblende—a radioactive mineral that contains uranium and thorium. They discovered that even with the uranium and thorium removed, the pitchblende was still highly radioactive. Eventually, the Curies found the elements polonium and radium in the pitchblende. They opted to name element 84 polonium after Marie Curie’s homeland, Poland—which was at that time under Russian, German, and Austro-Hungarian control—in part to raise awareness of the country’s lack of independence.

Polonium was first used in textile mills and in factories to reduce static electricity. During the Manhattan Project (the World War II-era effort to produce the world’s first nuclear weapon), polonium was used in some weapon designs. But polonium became notorious when, in 2006, it was used in the poisoning of Alexander Litvinenko, a former Soviet intelligence officer who had defected to the United Kingdom. Only a few micrograms of polonium-210 were sufficient to cause Litvinenko’s death from radiation sickness.

Polonium’s most notable quality is its radioactivity. It is the most radioactive naturally occurring element: and less than one microgram of polonium-210 can be lethal! Although it’s usually handled in quantities that are too small to be visible to the naked eye, polonium is a silver-grey semi-metal that dissolves in dilute acids. 

Polonium’s radioactivity is such that it generates heat, which is why it has been used in space. For example, the Soviet Union used polonium-210 as a heat source in moon rovers and satellites to prevent freezing.

Polonium is also used in antistatic devices, which are used in factories or industrial manufacturing (rather than to keep people from getting shocked by light switches!). However, polonium is so radioactive that researchers have increasingly looked for other substances that can remove static.

Almost all polonium compounds are made in laboratories, although you’ll find PbPo in nature (because polonium decays to form lead). Polonides are compounds of polonium and one other element. For example, polonides of calcium, barium, thulium, and others have been produced.

Researchers have identified 42 polonium isotopes. Polonium has no stable (non-radioactive) isotopes. Polonium-210 is the most common isotope, with a half-life of around 138 days. Polonium-209 has the longest half-life of any polonium isotope: its half-life is around 125 years. The shortest-lived polonium isotopes have half-lives of mere microseconds (a microsecond is one millionth of a second!).

Historically, polonium was extracted from uranium ores. However, this is a difficult process, because polonium is found in nature only in trace amounts. Today, all the world’s polonium is produced at the Ozersk nuclear reactor near Chelyabinsk, Russia. Only around 100 grams of polonium are produced each year. (For context, most apples weigh between 150 and 250 grams!)