Naturally occurring radioactive element - Polonium-210

Polonium was discovered by Marie Sklodowska-Curie and Pierre Curie in 1898 and was named after Marie´s native land of Poland (Latin: Polonia). This element was the first one discovered by them while they were investigating the cause of radioactivity in pitchblende. Polonium-210 (Po-210) is a radioactive element that occurs naturally and is present in the environment at extremely low concentrations. Po-210 has a half-life of 138 days. It decays to stable lead-206 by emitting alpha particle.

Po-210 is produced during the decay of naturally occurring uranium-238 and hence is widely distributed in small amounts in the earth´s crust. Uranium ores contain less than 0.1 mg Po-210 per ton. In the environment, Po-210 is produced from the decay of Radon-222 gas. Although direct root uptake by plants is generally small, Po-210 can be deposited on broad-leaved vegetables. Deposition from the atmosphere on tobacco leaves results in elevated concentrations of Po-210 in tobacco smoke. There are tiny amounts of Po-210 in our bodies. Po-210 can be produced artificially in nuclear reactors by irradiating stable bismuth-209.

Po-210 is used in neutron sources (where it is mixed or alloyed with beryllium). It is also used in devices that eliminate static electricity in machinery where it can be caused by processes such as paper rolling, manufacturing sheet plastics, and spinning synthetic fibres. Static eliminators typically contain from one to tens of GBq of radioactivity. One should ensure physical security of these sources to prevent its misuse.

Due to the alpha decay, the energy released from one gram is 140 watts, and a capsule containing about half a gram will spontaneously reach a temperature of 500°C. As a result it has been used as a lightweight heat source to power thermoelectric cells in satellites and short-term space missions. It is a fairly volatile (50% is vaporized in air in 45 hours at 55°C) silvery-grey soft metal.
Po-210 is highly radioactive and chemically toxic element. As an alpha-emitter Po-210 represents a radiation hazard only if taken into the body. Direct damage occurs from energy absorption into tissues from alpha particles. It is not an external hazard.

Po-210 can enter the body through eating and drinking of contaminated food, breathing contaminated air or through a wound. The biological half-time is approximately 50 days. If taken into the body, Po-210 is subsequently excreted, mostly through faeces but some is excreted through urine and other pathways.