Polonium-210 Polonium is a radioactive substance that can be found throughout our natural environment. Polonium was discovered in the late 1800s when Marie and Pierre Cu-rie were trying to determine why something they were studying was still radioactive even after they had ex-tracted some of the radioactive contents. When it is purified, polonium melts at a low tempera-ture and can be volatile. There are different types of po-lonium due to a varying number of neutrons in the nu-cleus of the isotopes. We are aware of 25 isotopes of po-lonium; polonium-210 is one of them. The polonium isotopes that are known are radioactive, but most are very short-lived and decay rapidly. Of the 25 known isotopes, there are three that have longer half-lives. Those isotopes are polonium-208, polonium-209, and polonium-210. The most widely used and the one occurring most in nature is polonium-210. Polonium-210 has a half-life* of 138 days, and it decays to stable lead-206 by emitting an alpha particle (an alpha par-ticle has two protons and two neutrons). With a specific activity of 166 TBq/g, one microgram of ingested polo-nium would deliver a committed effective dose equivalent of approximately 40 Sv (4,000 rem). This value is based on human and animal studies conducted in the 1950s that showed that approximately 10 percent of ingested polo-nium is absorbed by blood (Harrison et al. 2007). Origins Polonium-210 exists naturally; there are tiny amounts in our bodies and small quantities in the soil and air. Al-though it can be produced by the chemical processing of uranium ores or minerals, uranium ores contain less than 0.1 milligram of polonium-210 per ton. Although it exists naturally, to generate useful quanti-ties polonium-210 needs to be made in a nuclear reactor by bombarding a stable product with neutrons. The sta-ble product becomes radioactive and decays according to a certain half-life, and polonium-210 is left. This method can produce gram amounts of polonium-210. Uses Polonium-210 has many uses, but is most well known for its use in static eliminators. These devices, which have a very small amount of the radioactive material mixed in a matrix and put on a foil, are used in manu-facturing environments to get rid of static that can be generated by routine processes like making tape, rolling paper, and smoothing metals. It can also be used to re-move dust particles in environments that need to be “clean,” like computer-chip manufacturing and photo-graphic-film processing. Static eliminators typically range from a few MBq (hundreds of microcuries) of radioactivity to tens of GBq (tenths of curies) for certain industrial applications. Polo-nium-210 can also be combined with beryllium to pro-duce neutron sources. Health Effects If a source of polonium-210 is outside of the body, it is not a health hazard. It can be a health hazard if it is taken inside the body. The alpha particles emitted by polonium-210 do not travel far and deposit their energy in a very small area. This is why they cannot penetrate the layer of skin on our bodies, but do damage internal structures by killing or injuring nearby cells. The most common ways to get radioactivity, including polonium-210, inside the body are by eating it, breath-ing it, or drinking it. If polonium is taken orally (by mouth), excretion is largely via the feces (Stannard 1988). What is left will travel throughout the body via the bloodstream, with much of it finally ending up in the spleen and kidneys. If polonium is inhaled, some of it will stay in the lungs. Almost half of the polonium that stays in the body can be found in the spleen, kidneys, and liver. A small por-tion will go to the bone marrow while the rest is distrib-uted throughout the body, mainly in the blood, in the lymph nodes, and on the mucous lining of the respira-tory tract. Alpha particles emitted from polonium-210 can disrupt cell structures, fragment nuclei, damage DNA, and cause cell death. The extent of biological damage caused from alpha emit-ters like polonium-210 in the gastrointestinal (GI) tract is not well known. Some data gathered from animal stud-ies during the 1960s indicated that alpha emitters actu-ally deliver less dose to the mucosal lining per Bq than beta or gamma emitters. This may be due to the short range of the alpha particle. As food traverses through the GI tract, it moves through by muscular contractions in clusters that are referred to as a bolus of food. As a bolus containing alpha emitters traverses the GI tract, only alphas that are on the edge of the bolus are close enough to the epithelial cells of the GI tract to result in radiation dose to the intestinal lining. Bone marrow depression will occur with 5 Gy (500 rad) whole-body single radiation dose and is likely to be the principal biological effect for acutely lethal intakes. Polonium-210 inside someone’s body is not detectable with standard radiation survey instruments used out-side that person’s body. Testing the individual’s urine or feces for alpha radiation would be the method of detec-tion. For someone to be poisoned with polonium-210, a large radiation dose would be needed—a dose not possi-ble with naturally occurring polonium-210, but possible with man made Po-210. Physical half-life of 210Po = 138 days Biological half-life of 210Po = 50 days Effective half-life of 210Po = 36.7 days Specific activity of 210Po = 1.66x1014 Bq/g Alpha energy = 5.3 MeV
Posted on: Fri, 08 Nov 2013 23:15:20 +0000
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