FAQs 2006 - Polonium-210
Factsheets & FAQs
Polonium-210
Basic Facts
Polonium-210 (Po-210) is a radioactive element that occurs naturally and is present in the
environment at extremely low concentrations.
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 pitchblende radioactivity.
It is a fairly volatile (50% is vaporized in air in 45 hours at 55°C) silvery-grey soft metal.
Po-210 has a half-life of 138 days. This is the time it takes for the activity to decrease by half
due to a process of radioactive decay. Po-210 decays to stable lead-206 by emitting alpha
particles, accompanied by very low intensity gamma rays. The majority of the time Po-210
decays by emission of alpha particles only, not by emission of an alpha particle and a gamma
ray. Only about one in a 100,000 decays results in the emission of a gamma ray. Alpha
spectroscopy is the best method of measuring this isotope.
Origin
Being produced during the decay of naturally occurring uranium-238, polonium-210 is widely
distributed in small amounts in the earth's crust. Although it can be produced by the chemical
processing of uranium ores or minerals, uranium ores contain less than 0.1 mg Po-210 per ton.
Because Po-210 is produced from the decay of radon-222 gas, it can be found in the
atmosphere from which it is deposited on the earth's surface. 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 manufactured artificially by irradiating stable bismuth-209 with thermal
neutrons resulting in the formation of radioactive Bi-210, which decays (half-life 5 days) into
Po-210. Polonium may now be made in milligram amounts in this procedure which uses high
neutron fluxes found in nuclear reactors. Only about 100 grams are produced each year,
making polonium exceedingly rare.
Uses
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. Brushes
containing Po-210 are used to remove accumulated dust from photographic films and camera
lenses. Static eliminators typically contain from one to tens of GBq of radioactivity.
Po-210 emits so many alpha particles each second that 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
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cells in satellites. A Po-210 heat source was also used in each of the Lunokhod rovers
deployed on the surface of the Moon, to keep their internal components warm during the lunar
nights. However, because of its short half-life Po-210 cannot provide power for long-term
space missions and has been phased out of use in this application. Polonium is not subject to
IAEA safeguards.
Toxicity
Po-210 is highly radioactive and chemically toxic element. Direct damage occurs from energy
absorption into tissues from alpha particles. As an alpha-emitter Po-210 represents a radiation
hazard only if taken into the body. It's important to note that alpha particles do not travel very
far - no more than a few centimetres in air. They are stopped by a sheet of paper or by the
dead layer of outer skin on our bodies. Therefore, external exposure from Po-210 is not a
concern and Po-210 does not represent a risk to human health as long as Po-210 remains
outside the body. Most traces of it on a person can be eliminated through careful hand-
washing and showering.
Po-210 can enter the body through eating and drinking of contaminated food, breathing
contaminated air or through a wound. The biological half-time (the time for the level of Po-
210 in the body to fall by half) 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. People who come into contact with a person contaminated by Po-210 will not be at
risk unless they ingest or inhale bodily fluids of the contaminated person.
Responsible/Contact: Office of Public Information and Communication
(From 2006)