Probably for the first time ever, the element polonium 210 has hit the headlines, in connection with its use as a poison to kill Alexander Litvinenko, an outspoken critic of the Putin regime. Polonium was discovered by Marie Curie
Probably for the first time ever, the element polonium 210 has hit the headlines, in connection with its use as a poison to kill Alexander Litvinenko, an outspoken critic of the Putin regime. Polonium was discovered by Marie Curie (and her husband Pierre), among the products heroically obtained from extracting four tons of uranium ore (pitchblende), working for four years in an unheated shed, boiling the rock in vats of concentrated acids. At that time, only uranium and thorium were known to be radioactive, and the far more intensely radioactive radium and polonium were revealed and isolated by the procedure of fractional crystallization, probably the most laborious in chemistry. Marie named polonium after her native Poland. Polonium 210 has a half life of about 138 days, and emits five thousand times the amount of radiation as an equal quantity of radium does. Put differently, one milligram of polonium 210 (210Po) emits as much radiation as 5 grams of radium. Polonium is an alpha emitter (i.e. when the nucleus undergoes radioactive decay it releases alpha particles), and so it must be inhaled, swallowed or injected to exert any toxic effects, since alpha particles are stopped by the skin and do not penetrate thus into the body. Only one decay out of every 100,000 results in the emission of a gamma ray along with an alpha particle, while the rest are pure alpha decays. This makes the material more difficult to detect than many other radioactive isotopes, and this is most sensitively done using an alpha spectrometer to measure alpha particles rather than by measuring gamma rays.
The decay of polonium releases a considerable amount of energy and half a gram of the material will quickly reach a temperature of 500 degrees Celsius. A quantity of 210Po equal to just a few curies (one curie is equal to one gram of radium and hence is equal to around 0.2 milligrams of 210Po) is observed to emit a blue glow from gamma rays exciting surrounding air molecules. One gram of 210Po produces 140 Watts of power, and accordingly it has been used as a heat source to power thermoelectric cells in satellites. Because polonium is a highly radioactive and toxic element it is very difficult to handle, and even microgram (millionths of a gram) quantities of 210Po are extremely dangerous, requiring specialized equipment and strict containment procedures. Alpha particles emitted by 210Po will damage internal organic tissue easily if polonium is ingested, inhaled or injected. The maximum permitted body burden for ingested polonium is reckoned at just 1,100 becquerels (0.03 microcurie - 30 billionths of a Curie), which is equivalent to a particle weighing only 6.8 × 10-12 gram (6.8 millonths of a microgram). Weight for weight, polonium is 250 billion times as toxic as prussic acid (hydrogen cyanide).
I discovered only the other day that there is a relation between polonium and lung cancers caused by smoking cigarettes. Indeed, 210Po is the one individual component of cigarette smoke shown to cause cancers by inhalation. In studies of laboratory animals, lung tumours were found to develop at levels far lower than the dose received by a heavy smoker. The history is that lung cancer rates among men climbed from being a rare disease that occurred at a rate of 4 in every 100,000 people per year, to 72/100,000 by 1980, making it the number one fatal cancer, despite an almost 20% decrease in levels of smoking during that same period. This coincided with a tripling in the levels of 210Po found in American tobacco, a result of tobacco growers using superphosphate fertilizers. Calcium phosphate ores tend to concentrate uranium, which decays to radon which then breaks down to 210Po (a "daughter product"). Indeed, soils associated with phosphate ores have uranium concentrations from 50 - 1000 parts per million (ppm), and far in excess of the the 2 - 3 ppm usually found. The 210Po becomes attached to the sticky hairs on th