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Polonium 210

Discussion in 'Habari na Hoja mchanganyiko' started by zubedayo_mchuzi, Feb 20, 2012.

  1. zubedayo_mchuzi

    zubedayo_mchuzi JF-Expert Member

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    Feb 20, 2012
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    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 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.

    About Illicit Ttrafficking Incidents Involving Po-210 Of the approximately 520 incidents reported by States to the IAEA´s Illicit Trafficking Data Base since 2004, 14 incidents have involved industrial Po-210 sources. Three of these incidents occurred in 2006. The incidents involved the theft, loss, or disposal of static eliminators and air ionizers containing sealed Po-210 sources. Po-210 used in these sealed sources is bound with other materials and extraction of the Po-210 would require some chemical treatment in a laboratory.


    By mass, polonium-210 is around 250,000 times more toxic than hydrogen cyanide (the actual LD50 for 210Po is less than 1 microgram for an average adult (see below) compared with about 250 milligrams for hydrogen cyanide. The main hazard is its intense radioactivity (as an alpha emitter), which makes it very difficult to handle safely: one gram of Po will self-heat to a temperature of around 500 °C (932 °F).[4] Even in microgram amounts, handling 210Po is extremely dangerous, requiring specialized equipment (a.o., alpha glove box under depression and equipped with high performance filters), adequate monitoring, and strict handling procedures to avoid any contamination. Alpha particles emitted by polonium will damage organic tissue easily if polonium is ingested, inhaled, or absorbed, although they do not penetrate the epidermis and hence are not hazardous as long as the alpha particles remain outside of the body. Meanwhile, wearing chemically resistant and "intact" gloves is a mandatory precaution to avoid transcutaneous diffusion of polonium directly through the skin. Polonium delivered in concentrated nitric acid can easily diffuse through inadequate gloves (e.g., latex gloves) or the acid may damage the gloves.

    Acute effects

    The median lethal dose (LD50) for acute radiation exposure is generally about 4.5 Sv.The committed effective dose equivalent 210Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled.[37] Since 210Po has an activity of 166 TBq per gram (4,500 Ci/g)[37] (1 gram produces 166×1012 decays per second), a fatal 4.5 Sv (J/kg) dose can be caused by ingesting 8.8 MBq (238 microcuries, µCi), about 50 nanograms (ng), or inhaling 1.8 MBq (48 µCi), about 10 ng. One gram of 210Po could thus in theory poison 20 million people of whom 10 million would die. The actual toxicity of 210Po is lower than these estimates, because radiation exposure that is spread out over several weeks (the biological half-life of polonium in humans is 30 to 50 days[38]) is somewhat less damaging than an instantaneous dose. It has been estimated that a median lethal dose of 210Po is 0.015 GBq (0.4 mCi), or 0.089 micrograms, still an extremely small amount.

    Long term (chronic) effects

    In addition to the acute effects, radiation exposure (both internal and external) carries a long-term risk of death from cancer of 5–10% per Sv. The general population is exposed to small amounts of polonium as a radon daughter in indoor air; the isotopes 214Po and 218Po are thought to cause the majority[41] of the estimated 15,000-22,000 lung cancer deaths in the US every year that have been attributed to indoor radon.Tobacco smoking causes additional exposure to polonium

    SOURCE.http://en.wikipedia.org/wiki/Polonium,
    www.iaea.org/Publications/Factsheets/English/polonium210.html
     
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