Polonium

Polonium is a chemical element with symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238. Though slightly longer-lived isotopes exist, they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.

Polonium was discovered in 1898 by Marie and Pierre Curie, when it was extracted from uranium ore and identified solely by its strong radioactivity: it was the first element to be so discovered. Polonium was named after Marie Curie's homeland of Poland. Polonium has few applications, and those are related to its radioactivity: heaters in space probes, antistatic devices, and sources of neutrons and alpha particles. Besides the radioactivity polonium is chemically extremely toxic.

Polonium,  84Po
Polonium
General properties
Pronunciation/pəˈloʊniəm/ (pə-LOH-nee-əm)
Allotropesα, β
Appearancesilvery
Mass number209 (most stable isotope)
Polonium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Te

Po

Lv
bismuthpoloniumastatine
Atomic number (Z)84
Groupgroup 16 (chalcogens)
Periodperiod 6
Blockp-block
Element category  post-transition metal, but this status is disputed
Electron configuration[Xe] 4f14 5d10 6s2 6p4
Electrons per shell
2, 8, 18, 32, 18, 6
Physical properties
Phase at STPsolid
Melting point527 K ​(254 °C, ​489 °F)
Boiling point1235 K ​(962 °C, ​1764 °F)
Density (near r.t.)alpha: 9.196 g/cm3
beta: 9.398 g/cm3
Heat of fusionca. 13 kJ/mol
Heat of vaporization102.91 kJ/mol
Molar heat capacity26.4 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) (846) 1003 1236
Atomic properties
Oxidation states−2, +2, +4, +5,[1] +6 (an amphoteric oxide)
ElectronegativityPauling scale: 2.0
Ionization energies
  • 1st: 812.1 kJ/mol
Atomic radiusempirical: 168 pm
Covalent radius140±4 pm
Van der Waals radius197 pm
Color lines in a spectral range
Spectral lines of polonium
Other properties
Crystal structurecubic
Cubic crystal structure for polonium

α-Po
Crystal structurerhombohedral
Rhombohedral crystal structure for polonium

β-Po
Thermal expansion23.5 µm/(m·K) (at 25 °C)
Thermal conductivity20 W/(m·K) (?)
Electrical resistivityα: 0.40 µΩ·m (at 0 °C)
Magnetic orderingnonmagnetic
CAS Number7440-08-6
History
Namingafter Polonia, Latin for Poland, homeland of Marie Curie
DiscoveryPierre and Marie Curie (1898)
First isolationWilly Marckwald (1902)
Main isotopes of polonium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
208Po syn 2.898 y α 204Pb
β+ 208Bi
209Po syn 125.2 y[2] α 205Pb
β+ 209Bi
210Po trace 138.376 d α 206Pb

Characteristics

210Po is an alpha emitter that has a half-life of 138.4 days; it decays directly to its stable daughter isotope, 206Pb. A milligram (5 curies) of 210Po emits about as many alpha particles per second as 5 grams of 226Ra.[3] A few curies (1 curie equals 37 gigabecquerels, 1 Ci = 37 GBq) of 210Po emit a blue glow which is caused by ionisation of the surrounding air.

About one in 100,000 alpha emissions causes an excitation in the nucleus which then results in the emission of a gamma ray with a maximum energy of 803 keV.[4][5]

Solid state form

Alpha po lattice
The alpha form of solid polonium.

Polonium is a radioactive element that exists in two metallic allotropes. The alpha form is the only known example of a simple cubic crystal structure in a single atom basis at STP, with an edge length of 335.2 picometers; the beta form is rhombohedral.[6][7][8] The structure of polonium has been characterized by X-ray diffraction[9][10] and electron diffraction.[11]

210Po (in common with 238Pu) has the ability to become airborne with ease: if a sample is heated in air to 55 °C (131 °F), 50% of it is vaporized in 45 hours to form diatomic Po2 molecules, even though the melting point of polonium is 254 °C (489 °F) and its boiling point is 962 °C (1,764 °F).[12][13][1] More than one hypothesis exists for how polonium does this; one suggestion is that small clusters of polonium atoms are spalled off by the alpha decay.

Chemistry

The chemistry of polonium is similar to that of tellurium, although it also shows some similarities to its neighbor bismuth due to its metallic character. Polonium dissolves readily in dilute acids but is only slightly soluble in alkalis. Polonium solutions are first colored in pink by the Po2+ ions, but then rapidly become yellow because alpha radiation from polonium ionizes the solvent and converts Po2+ into Po4+. This process is accompanied by bubbling and emission of heat and light by glassware due to the absorbed alpha particles; as a result, polonium solutions are volatile and will evaporate within days unless sealed.[14][15] At pH about 1, polonium ions are readily hydrolyzed and complexed by acids such as oxalic acid, citric acid, and tartaric acid.[16]

Compounds

Polonium has no common compounds, and almost all of its compounds are synthetically created; more than 50 of those are known.[17] The most stable class of polonium compounds are polonides, which are prepared by direct reaction of two elements. Na2Po has the antifluorite structure, the polonides of Ca, Ba, Hg, Pb and lanthanides form a NaCl lattice, BePo and CdPo have the wurtzite and MgPo the nickel arsenide structure. Most polonides decompose upon heating to about 600 °C, except for HgPo that decomposes at ~300 °C and the lanthanide polonides, which do not decompose but melt at temperatures above 1000 °C. For example, PrPo melts at 1250 °C and TmPo at 2200 °C.[18] PbPo is one of the very few naturally occurring polonium compounds, as polonium alpha decays to form lead.[19]

Polonium hydride (PoH
2
) is a volatile liquid at room temperature prone to dissociation; it is thermally unstable.[18] Water is the only other known hydrogen chalcogenide which is a liquid at room temperature; however, this is due to hydrogen bonding. The two oxides PoO2 and PoO3 are the products of oxidation of polonium.[20]

Halides of the structure PoX2, PoX4 and PoF6 are known. They are soluble in the corresponding hydrogen halides, i.e., PoClX in HCl, PoBrX in HBr and PoI4 in HI.[21] Polonium dihalides are formed by direct reaction of the elements or by reduction of PoCl4 with SO2 and with PoBr4 with H2S at room temperature. Tetrahalides can be obtained by reacting polonium dioxide with HCl, HBr or HI.[22]

Other polonium compounds include potassium polonite as a polonite, polonate, acetate, bromate, carbonate, citrate, chromate, cyanide, formate, (II) and (IV) hydroxides, nitrate, selenate, selenite, monosulfide, sulfate, disulfate and sulfite.[21][23]

Polonium compounds[22][24]
Formula Color m.p. (°C) Sublimation
temp. (°C)
Symmetry Pearson symbol Space group No a (pm) b(pm) c(pm) Z ρ (g/cm3) ref
PoO2 pale yellow 500 (dec.) 885 fcc cF12 Fm3m 225 563.7 563.7 563.7 4 8.94 [25]
PoCl2 dark ruby red 355 130 orthorhombic oP3 Pmmm 47 367 435 450 1 6.47 [26]
PoBr2 purple-brown 270 (dec.) [27]
PoCl4 yellow 300 200 monoclinic [26]
PoBr4 red 330 (dec.) fcc cF100 Fm3m 225 560 560 560 4 [27]
PoI4 black [28]

Oxides

Hydrides

Halides

  • PoX2 (except PoF2)
  • PoX4
  • PoF6
  • PoBr2Cl2 (salmon pink)

Isotopes

Polonium has 33 known isotopes, all of which are radioactive. They have atomic masses that range from 188 to 220 u. 210Po (half-life 138.376 days) is the most widely available and is made via neutron capture by natural bismuth. The longer-lived 209Po (half-life 125.2±3.3 years, longest-lived of all polonium isotopes)[2] and 208Po (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron.[29]

History

Tentatively called "radium F", polonium was discovered by Marie and Pierre Curie in 1898,[30][31] and was named after Marie Curie's native land of Poland (Latin: Polonia).[32][33] Poland at the time was under Russian, German, and Austro-Hungarian partition, and did not exist as an independent country. It was Curie's hope that naming the element after her native land would publicize its lack of independence.[34] Polonium may be the first element named to highlight a political controversy.[34]

This element was the first one discovered by the Curies while they were investigating the cause of pitchblende radioactivity. Pitchblende, after removal of the radioactive elements uranium and thorium, was more radioactive than the uranium and thorium combined. This spurred the Curies to search for additional radioactive elements. They first separated out polonium from pitchblende in July 1898, and five months later, also isolated radium.[14][30][35] German scientist Willy Marckwald successfully isolated 3 milligrams of polonium in 1902, though at the time he believed it was a new element, which he dubbed "radio-tellurium", and it was not until 1905 that it was demonstrated to be the same as polonium.[36][37]

In the United States, polonium was produced as part of the Manhattan Project's Dayton Project during World War II. It was a critical part of the implosion-type nuclear weapon design used in the Fat Man bomb on Nagasaki in 1945. Polonium and beryllium were the key ingredients of the 'urchin' detonator at the center of the bomb's spherical plutonium pit.[38] The urchin ignited the nuclear chain reaction at the moment of prompt-criticality to ensure the bomb did not fizzle.[38]

Much of the basic physics of polonium was classified until after the war. The fact that it was used as an initiator was classified until the 1960s.[39]

The Atomic Energy Commission and the Manhattan Project funded human experiments using polonium on five people at the University of Rochester between 1943 and 1947. The people were administered between 9 and 22 microcuries (330 and 810 kBq) of polonium to study its excretion.[40][41][42]

Occurrence and production

Polonium is a very rare element in nature because of the short half-life of all its isotopes. 210Po, 214Po, and 218Po appear in the decay chain of 238U; thus polonium can be found in uranium ores at about 0.1 mg per metric ton (1 part in 1010),[43][44] which is approximately 0.2% of the abundance of radium. The amounts in the Earth's crust are not harmful. Polonium has been found in tobacco smoke from tobacco leaves grown with phosphate fertilizers.[45][46][47]

Because it is present in small concentrations, isolation of polonium from natural sources is a tedious process. The largest batch of the element ever extracted, performed in the first half of the 20th century, contained only 40 Ci (1.5 TBq) (9 mg) of polonium-210 and was obtained by processing 37 tonnes of residues from radium production.[48] Polonium is now usually obtained by irradiating bismuth with high-energy neutrons or protons.[14][49]

In 1934, an experiment showed that when natural 209Bi is bombarded with neutrons, 210Bi is created, which then decays to 210Po via beta-minus decay. The final purification is done pyrochemically followed by liquid-liquid extraction techniques.[50] Polonium may now be made in milligram amounts in this procedure which uses high neutron fluxes found in nuclear reactors.[49] Only about 100 grams are produced each year, practically all of it in Russia, making polonium exceedingly rare.[51][52]

This process can cause problems in lead-bismuth based liquid metal cooled nuclear reactors such as those used in the Soviet Navy's K-27. Measures must be taken in these reactors to deal with the unwanted possibility of 210Po being released from the coolant.[53][54]

The longer-lived isotopes of polonium, 208Po and 209Po, can be formed by proton or deuteron bombardment of bismuth using a cyclotron. Other more neutron-rich and more unstable isotopes can be formed by the irradiation of platinum with carbon nuclei.[55]

Applications

Polonium-based sources of alpha particles were produced in the former Soviet Union.[56] Such sources were applied for measuring the thickness of industrial coatings via attenuation of alpha radiation.[57]

Because of intense alpha radiation, a one-gram sample of 210Po will spontaneously heat up to above 500 °C (932 °F) generating about 140 watts of power. Therefore, 210Po is used as an atomic heat source to power radioisotope thermoelectric generators via thermoelectric materials.[3][14][58][59] For example, 210Po heat sources were used in the Lunokhod 1 (1970) and Lunokhod 2 (1973) Moon rovers to keep their internal components warm during the lunar nights, as well as the Kosmos 84 and 90 satellites (1965).[56][60]

The alpha particles emitted by polonium can be converted to neutrons using beryllium oxide, at a rate of 93 neutrons per million alpha particles.[58] Thus Po-BeO mixtures or alloys are used as a neutron source, for example, in a neutron trigger or initiator for nuclear weapons[14][61] and for inspections of oil wells. About 1500 sources of this type, with an individual activity of 1,850 Ci (68 TBq), have been used annually in the Soviet Union.[62]

Polonium was also part of brushes or more complex tools that eliminate static charges in photographic plates, textile mills, paper rolls, sheet plastics, and on substrates (such as automotive) prior to the application of coatings.[63] Alpha particles emitted by polonium ionize air molecules that neutralize charges on the nearby surfaces.[64][65] Some anti-static brushes contain up to 500 microcuries (20 MBq) of 210Po as a source of charged particles for neutralizing static electricity.[66] In the US, the devices with no more than 500 μCi (19 MBq) of (sealed) 210Po per unit can be bought in any amount under a "general license",[67] which means that a buyer need not be registered by any authorities. Polonium needs to be replaced in these devices nearly every year because of its short half-life; it is also highly radioactive and therefore has been mostly replaced by less dangerous beta particle sources.[3]

Tiny amounts of 210Po are sometimes used in the laboratory and for teaching purposes—typically of the order of 4–40 kBq (0.11–1.08 μCi), in the form of sealed sources, with the polonium deposited on a substrate or in a resin or polymer matrix—are often exempt from licensing by the NRC and similar authorities as they are not considered hazardous. Small amounts of 210Po are manufactured for sale to the public in the United States as 'needle sources' for laboratory experimentation, and they are retailed by scientific supply companies. The polonium is a layer of plating which in turn is plated with a material such as gold, which allows the alpha radiation (used in experiments such as cloud chambers) to pass while preventing the polonium from being released and presenting a toxic hazard. According to United Nuclear, they typically sell between four and eight such sources per year.[68][69]

Polonium spark plugs were marketed by Firestone from 1940 to 1953. While the amount of radiation from the plugs was minuscule and not a threat to the consumer, the benefits of such plugs quickly diminished after approximately a month because of polonium's short half-life and because buildup on the conductors would block the radiation that improved engine performance. (The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard's prototype radium plug that preceded it, was that the radiation would improve ionization of the fuel in the cylinder and thus allow the motor to fire more quickly and efficiently.)[70][71]

Biology and toxicity

Overview

Polonium is highly dangerous and has no biological role.[14] By mass, polonium-210 is around 250,000 times more toxic than hydrogen cyanide (the LD50 for 210Po is less than 1 microgram for an average adult (see below) compared with about 250 milligrams for hydrogen cyanide[72]). The main hazard is its intense radioactivity (as an alpha emitter), which makes it difficult to handle safely. Even in microgram amounts, handling 210Po is extremely dangerous, requiring specialized equipment (a negative pressure alpha glove box 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 the body. 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.[73]

It has been reported that some microbes can methylate polonium by the action of methylcobalamin.[74][75] This is similar to the way in which mercury, selenium, and tellurium are methylated in living things to create organometallic compounds. Studies investigating the metabolism of polonium-210 in rats have shown that only 0.002 to 0.009% of polonium-210 ingested is excreted as volatile polonium-210.[76]

Acute effects

The median lethal dose (LD50) for acute radiation exposure is about 4.5 Sv.[77] The committed effective dose equivalent 210Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled.[78] So a fatal 4.5 Sv dose can be caused by ingesting 8.8 MBq (240 μCi), about 50 nanograms (ng), or inhaling 1.8 MBq (49 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[79]) is somewhat less damaging than an instantaneous dose. It has been estimated that a median lethal dose of 210Po is 15 megabecquerels (0.41 mCi), or 0.089 micrograms, still an extremely small amount.[80][81] For comparison, one grain of table salt is about 0.06 mg = 60 μg.[82]

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.[77] 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[83] of the estimated 15,000–22,000 lung cancer deaths in the US every year that have been attributed to indoor radon.[84] Tobacco smoking causes additional exposure to polonium.[85]

Regulatory exposure limits and handling

The maximum allowable body burden for ingested 210Po is only 1.1 kBq (30 nCi), which is equivalent to a particle massing only 6.8 picograms. The maximum permissible workplace concentration of airborne 210Po is about 10 Bq/m3 (3×10−10 µCi/cm3).[86] The target organs for polonium in humans are the spleen and liver.[87] As the spleen (150 g) and the liver (1.3 to 3 kg) are much smaller than the rest of the body, if the polonium is concentrated in these vital organs, it is a greater threat to life than the dose which would be suffered (on average) by the whole body if it were spread evenly throughout the body, in the same way as caesium or tritium (as T2O).

210Po is widely used in industry, and readily available with little regulation or restriction. In the US, a tracking system run by the Nuclear Regulatory Commission was implemented in 2007 to register purchases of more than 16 curies (590 GBq) of polonium-210 (enough to make up 5,000 lethal doses). The IAEA "is said to be considering tighter regulations ... There is talk that it might tighten the polonium reporting requirement by a factor of 10, to 1.6 curies (59 GBq)."[88] As of 2013, this is still the only alpha emitting byproduct material available, as a NRC Exempt Quantity, which may be held without a radioactive material license.

Polonium and its compounds must be handled in a glove box, which is further enclosed in another box, maintained at a slightly higher pressure than the glove box to prevent the radioactive materials from leaking out. Gloves made of natural rubber do not provide sufficient protection against the radiation from polonium; surgical gloves are necessary. Neoprene gloves shield radiation from polonium better than natural rubber.[89]

Well-known poisoning cases

20th century

Polonium was administered to humans for experimental purposes from 1943 to 1947; it was injected into four hospitalised patients, and orally given to a fifth. Studies such as this were funded by the Manhattan Project and the AEC and conducted at the University of Rochester. The objective was to obtain data on human excretion of polonium to correlate with more extensive data from rats. Patients selected as subjects were chosen because experimenters wanted persons who had not been exposed to polonium either through work or accident. All subjects had incurable diseases. Excretion of polonium was followed, and an autopsy was conducted at that time on the deceased patient to determine which organs absorbed the polonium. Patients' ages ranged from 'early thirties' to 'early forties'. The experiments were described in Chapter 3 of Biological Studies with Polonium, Radium, and Plutonium, National Nuclear Energy Series, Volume VI-3, McGraw-Hill, New York, 1950. Not specified is the isotope under study, but at the time polonium-210 was the most readily available polonium isotope. The DoE factsheet submitted for this experiment reported no follow up on these subjects.[90]

It has also been suggested that Irène Joliot-Curie was the first person to die from the radiation effects of polonium. She was accidentally exposed to polonium in 1946 when a sealed capsule of the element exploded on her laboratory bench. In 1956, she died from leukemia.[91]

According to the 2008 book The Bomb in the Basement, several deaths in Israel during 1957–1969 were caused by 210Po.[92] A leak was discovered at a Weizmann Institute laboratory in 1957. Traces of 210Po were found on the hands of Professor Dror Sadeh, a physicist who researched radioactive materials. Medical tests indicated no harm, but the tests did not include bone marrow. Sadeh died from cancer. One of his students died of leukemia, and two colleagues died after a few years, both from cancer. The issue was investigated secretly, and there was never any formal admission that a connection between the leak and the deaths had existed.[93]

21st century

The cause of death in the 2006 homicide of Alexander Litvinenko, a Russian KGB agent who had defected to the British MI6 intelligence agency, was determined to be 210Po poisoning.[94][95] According to Prof. Nick Priest of Middlesex University, an environmental toxicologist and radiation expert, speaking on Sky News on December 3, 2006, Litvinenko was probably the first person to die of the acute α-radiation effects of 210Po.[96]

Abnormally high concentrations of 210Po were detected in July 2012 in clothes and personal belongings of the Palestinian leader Yasser Arafat, a heavy smoker, who died on 11 November 2004 of uncertain causes. The spokesman for the Institut de Radiophysique in Lausanne, Switzerland, where those items were analyzed, stressed that the "clinical symptoms described in Arafat's medical reports were not consistent with polonium-210 and that conclusions could not be drawn as to whether the Palestinian leader was poisoned or not", and that "the only way to confirm the findings would be to exhume Arafat's body to test it for polonium-210."[97] On 27 November 2012 Arafat's body was exhumed, and samples were taken for separate analysis by experts from France, Switzerland and Russia.[98] On 12 October 2013, The Lancet published the group's finding that high levels of the element were found in Arafat's blood, urine, and in saliva stains on his clothes and toothbrush.[99] The French tests later found some polonium but stated it was from "natural environmental origin".[100] Following later Russian tests, Vladimir Uiba, the head of the Russian Federal Medical and Biological Agency, stated in December 2013 that Arafat died of natural causes, and they had no plans to conduct further tests.[100]

Treatment

It has been suggested that chelation agents, such as British Anti-Lewisite (dimercaprol), can be used to decontaminate humans.[101] In one experiment, rats were given a fatal dose of 1.45 MBq/kg (8.7 ng/kg) of 210Po; all untreated rats were dead after 44 days, but 90% of the rats treated with the chelation agent HOEtTTC remained alive for 5 months.[102]

Detection in biological specimens

Polonium-210 may be quantified in biological specimens by alpha particle spectrometry to confirm a diagnosis of poisoning in hospitalized patients or to provide evidence in a medicolegal death investigation. The baseline urinary excretion of polonium-210 in healthy persons due to routine exposure to environmental sources is normally in a range of 5–15 mBq/day. Levels in excess of 30 mBq/day are suggestive of excessive exposure to the radionuclide.[103]

Occurrence in humans and the biosphere

Polonium-210 is widespread in the biosphere, including in human tissues, because of its position in the uranium-238 decay chain. Natural uranium-238 in the Earth's crust decays through a series of solid radioactive intermediates including radium-226 to the radioactive noble gas radon-222, some of which, during its 3.8-day half-life, diffuses into the atmosphere. There it decays through several more steps to polonium-210, much of which, during its 138-day half-life, is washed back down to the Earth's surface, thus entering the biosphere, before finally decaying to stable lead-206.[104][105][106]

As early as the 1920s Antoine Lacassagne, using polonium provided by his colleague Marie Curie, showed that the element has a specific pattern of uptake in rabbit tissues, with high concentrations, particularly in liver, kidney, and testes.[107] More recent evidence suggests that this behavior results from polonium substituting for its congener sulfur, also in group 16 of the periodic table, in sulfur-containing amino-acids or related molecules[108] and that similar patterns of distribution occur in human tissues.[109] Polonium is indeed an element naturally present in all humans, contributing appreciably to natural background dose, with wide geographical and cultural variations, and particularly high levels in arctic residents, for example.[110]

Tobacco

Polonium-210 in tobacco contributes to many of the cases of lung cancer worldwide. Most of this polonium is derived from lead-210 deposited on tobacco leaves from the atmosphere; the lead-210 is a product of radon-222 gas, much of which appears to originate from the decay of radium-226 from fertilizers applied to the tobacco soils.[47][111][112][113][114]

The presence of polonium in tobacco smoke has been known since the early 1960s.[115][116] Some of the world's biggest tobacco firms researched ways to remove the substance—to no avail—over a 40-year period. The results were never published.[47]

Food

Polonium is found in the food chain, especially in seafood.[117][118]

See also

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Bibliography

External links

Chalcogen

The chalcogens () are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive element polonium (Po). The chemically uncharacterized synthetic element livermorium (Lv) is predicted to be a chalcogen as well. Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally meaning copper (the term was also used for bronze/brass, any metal in the poetic sense, ore or coin), and the Latinised Greek word genēs, meaning born or produced.Sulfur has been known since antiquity, and oxygen was recognized as an element in the 18th century. Selenium, tellurium and polonium were discovered in the 19th century, and livermorium in 2000. All of the chalcogens have six valence electrons, leaving them two electrons short of a full outer shell. Their most common oxidation states are −2, +2, +4, and +6. They have relatively low atomic radii, especially the lighter ones.Lighter chalcogens are typically nontoxic in their elemental form, and are often critical to life, while the heavier chalcogens are typically toxic. All of the chalcogens have some role in biological functions, either as a nutrient or a toxin. The lighter chalcogens, such as oxygen and sulfur, are rarely toxic and usually helpful in their pure form. Selenium is an important nutrient but is also commonly toxic. Tellurium often has unpleasant effects (although some organisms can use it), and polonium is always extremely harmful, both in its chemical toxicity and its radioactivity.

Sulfur has more than 20 allotropes, oxygen has nine, selenium has at least five, polonium has two, and only one crystal structure of tellurium has so far been discovered. There are numerous organic chalcogen compounds. Not counting oxygen, organic sulfur compounds are generally the most common, followed by organic selenium compounds and organic tellurium compounds. This trend also occurs with chalcogen pnictides and compounds containing chalcogens and carbon group elements.

Oxygen is generally extracted from air and sulfur is extracted from oil and natural gas. Selenium and tellurium are produced as byproducts of copper refining. Polonium and livermorium are most available in particle accelerators. The primary use of elemental oxygen is in steelmaking. Sulfur is mostly converted into sulfuric acid, which is heavily used in the chemical industry. Selenium's most common application is glassmaking. Tellurium compounds are mostly used in optical disks, electronic devices, and solar cells. Some of polonium's applications are due to its radioactivity.

Dayton Project

The Dayton Project was a research and development project to produce polonium during World War II, as part of the larger Manhattan Project to build the first atomic bombs. Work took place at several sites in and around Dayton, Ohio. Those working on the project were ultimately responsible for creating the polonium-based modulated neutron initiators which were used to begin the chain reactions in the atomic bombs.

The Dayton Project began in 1943 when Monsanto's Charles Allen Thomas was recruited by the Manhattan Project to coordinate the plutonium purification and production work being carried out at various sites. Scientists at the Los Alamos Laboratory calculated that a plutonium bomb would require a neutron initiator. The best-known neutron sources used radioactive polonium and beryllium, so Thomas undertook to produce polonium at Monsanto's laboratories in Dayton. While most Manhattan Project activity took place at remote locations, the Dayton Project was located in a populated, urban area. It ran from 1943 to 1949, when the Mound Laboratories were completed in nearby Miamisburg, Ohio, and the work moved there.

The Dayton Project developed techniques for extracting polonium from the lead dioxide ore in which it occurs naturally, and from bismuth targets that had been bombarded by neutrons in a nuclear reactor. Ultimately, polonium-based neutron initiators were used in both the gun-type Little Boy and the implosion-type Fat Man used in the atomic bombings of Hiroshima and Nagasaki respectively. The fact that polonium was used as an initiator was classified until the 1960s, but George Koval, a technician with the Manhattan Project's Special Engineer Detachment, penetrated the Dayton Project as a spy for the Soviet Union.

Hydrogen chalcogenide

Hydrogen chalcogenides (also chalcogen hydrides or hydrogen chalcides) are binary compounds of hydrogen with chalcogen atoms (elements of group 16: oxygen, sulfur, selenium, tellurium, and polonium). Water, the first chemical compound in this series, contains one oxygen atom and two hydrogen atoms, and is the most common compound on the Earth's surface.

Isotopes of polonium

Polonium (84Po) has 33 isotopes, all of which are radioactive, with between 186 and 227 nucleons. 210Po with a half-life of 138.376 days has the longest half-life of naturally occurring polonium. 209Po with a half-life of 125 years has the longest half-life of all isotopes of polonium. 209Po and 208Po (half-life 2.9 years) can be made through proton bombardment of bismuth in a cyclotron.

Lithium polonide

Lithium polonide is a chemical compound with the formula Li2Po. It is a polonide, a set of very chemically stable compounds of polonium.

Livermorium

Livermorium is a synthetic chemical element with symbol Lv and has an atomic number of 116. It is an extremely radioactive element that has only been created in the laboratory and has not been observed in nature. The element is named after the Lawrence Livermore National Laboratory in the United States, which collaborated with the Joint Institute for Nuclear Research (JINR) in Dubna, Russia to discover livermorium during experiments made between 2000 and 2006. The name of the laboratory refers to the city of Livermore, California where it is located, which in turn was named after the rancher and landowner Robert Livermore. The name was adopted by IUPAC on May 30, 2012. 4 isotopes of livermorium are known, with mass numbers between 290 and 293 inclusive; the longest-lived among them is livermorium-293 with a half-life of about 60 milliseconds. A fifth possible isotope with mass number 294 has been reported but not yet confirmed.

In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 16 as the heaviest chalcogen, although it has not been confirmed to behave as the heavier homologue to the chalcogen polonium. Livermorium is calculated to have some similar properties to its lighter homologues (oxygen, sulfur, selenium, tellurium, and polonium), and be a post-transition metal, although it should also show several major differences from them.

Magnesium polonide

Magnesium polonide (MgPo) is a salt of magnesium and polonium. It is a polonide, a set of very chemically stable compounds of polonium.

Marie Curie

Marie Skłodowska Curie (; French: [kyʁi]; Polish: [kʲiˈri]; born Maria Salomea Skłodowska; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first woman to win a Nobel Prize, the first person and only woman to win twice, and the only person to win a Nobel Prize in two different sciences. She was part of the Curie family legacy of five Nobel Prizes. She was also the first woman to become a professor at the University of Paris, and in 1995 became the first woman to be entombed on her own merits in the Panthéon in Paris.

She was born in Warsaw, in what was then the Kingdom of Poland, part of the Russian Empire. She studied at Warsaw's clandestine Flying University and began her practical scientific training in Warsaw. In 1891, aged 24, she followed her older sister Bronisława to study in Paris, where she earned her higher degrees and conducted her subsequent scientific work. She shared the 1903 Nobel Prize in Physics with her husband Pierre Curie and physicist Henri Becquerel. She won the 1911 Nobel Prize in Chemistry.

Her achievements included the development of the theory of radioactivity (a term that she coined), techniques for isolating radioactive isotopes, and the discovery of two elements, polonium and radium. Under her direction, the world's first studies into the treatment of neoplasms were conducted using radioactive isotopes. She founded the Curie Institutes in Paris and in Warsaw, which remain major centres of medical research today. During World War I she developed mobile radiography units to provide X-ray services to field hospitals.

While a French citizen, Marie Skłodowska Curie, who used both surnames, never lost her sense of Polish identity. She taught her daughters the Polish language and took them on visits to Poland. She named the first chemical element she discovered polonium, after her native country.Marie Curie died in 1934, aged 66, at a sanatorium in Sancellemoz (Haute-Savoie), France, of aplastic anemia from exposure to radiation in the course of her scientific research and in the course of her radiological work at field hospitals during World War I.

Modulated neutron initiator

A modulated neutron initiator is a neutron source capable of producing a burst of neutrons on activation. It is a crucial part of some nuclear weapons, as its role is to "kick-start" the chain reaction at the optimal moment when the configuration is prompt critical. It is also known as an internal neutron initiator. The initiator is typically placed in the center of the plutonium pit, and is activated by impact of the converging shock wave.

One of the key elements in the proper operation of a nuclear weapon is initiation of the fission chain reaction at the proper time. To obtain a significant nuclear yield, sufficient neutrons must be present within the supercritical core at the right time. If the chain reaction starts too soon ("predetonation"), the result will be only a 'fizzle yield', well below the design specification, therefore low spontaneous neutron emission of the pit material is crucial. If it occurs too late, the core will have begun to expand and disassemble into a less-dense state, leading to a lowered yield (less of the core material undergoes fission) or no yield at all (the core is no longer a critical mass).

As a general rule, 80 generations of neutron multiplication, in a nuclear (e.g. heavy water) fission reactor, are required in order to achieve explosion-yield equivalent; it must be achieved cca. yield of first 40 neutron generations, in order for a nuclear weapon to be "properly activated."

For boosted fission weapons, the size of the centrally placed initiator is critical and has to be as small as possible. The use of an external neutron source allows more flexibility, such as variable yields.

Poisoning of Alexander Litvinenko

Alexander Litvinenko was a former officer of the Russian Federal Security Service (FSB) and KGB, who fled from court prosecution in Russia and received political asylum in the United Kingdom.

On 1 November 2006, Litvinenko suddenly fell ill and was hospitalized. He died three weeks later, becoming the first confirmed victim of lethal polonium-210-induced acute radiation syndrome. Litvinenko's allegations about the misdeeds of the FSB and his public deathbed accusations that Russian president Vladimir Putin was behind his unusual malady resulted in worldwide media coverage.

Subsequent investigations by British authorities into the circumstances of Litvinenko's death led to serious diplomatic difficulties between the British and Russian governments. No charges were ever laid but a non-judicial public hearing was put on in 2014–2015, during which the Scotland Yard representative witnessed that "the evidence suggests that the only credible explanation is in one way or another the Russian state is involved in Litvinenko's murder". Another witness stated that Dmitry Kovtun had been speaking openly about the plan to kill Litvinenko that was intended to "set an example" as a punishment for a "traitor". The main suspect in the case, a former officer of the Russian Federal Protective Service (FSO), Andrey Lugovoy, remains in Russia.

Polonide

A polonide is a chemical compound of the radioactive element polonium with any element less electronegative than polonium. Polonides are usually prepared by a direct reaction between the elements at temperatures of around 300–400 °C. They are amongst the most chemically stable compounds of polonium, and can be divided into two broad groups:

ionic polonides, which appear to contain the Po2− anion;

intermetallic polonides, in which the bonding is more complex.Some polonides are intermediate between these two cases and others are non-stoichiometric compounds. Alloys containing polonium are also classed as polonides. As polonium is immediately below tellurium in the periodic table, there are many chemical and structural similarities between polonides and tellurides.

Polonium dichloride

Polonium dichloride is a chemical compound of the radioactive metalloid polonium and chlorine. Its chemical formula is PoCl2.

Polonium hexafluoride

Polonium hexafluoride (PoF6) is a possible chemical compound of polonium and fluorine and one of the seventeen known binary hexafluorides.

Polonium hydride

Polonium hydride (also known as polonium dihydride, hydrogen polonide, or polane) is a chemical compound with the formula PoH2. It is a liquid at room temperature, the second hydrogen chalcogenide with this property after water. It is very unstable chemically and tends to decompose into elemental polonium and hydrogen; like all polonium compounds, it is highly radioactive. It is a volatile and very labile compound, from which many polonides can be derived.

Polonium monoxide

Polonium monoxide (also known as polonium(II) oxide) is a chemical compound with the formula PoO. It is one of three oxides of polonium, the other two being polonium dioxide (PoO2) and polonium trioxide (PoO3). It is an interchalcogen.

Polonium tetrachloride

Polonium tetrachloride (also known as polonium(IV) chloride) is a chemical compound with the formula PoCl4. It is a hygroscopic bright yellow crystalline solid at room temperature. Above 200 °C, it tends to decompose into polonium dichloride and excess chlorine, similar to selenium tetrachloride and tellurium tetrachloride.

Potassium polonide

Potassium polonide is a chemical compound with the formula K2Po. It is a polonide, a set of very chemically stable compounds of polonium.

Radiohalo

Radiohalos or pleochroic halos are microscopic, spherical shells of discolouration (pleochroism) within minerals such as biotite that occur in granite and other igneous rocks. The shells are zones of radiation damage caused by the inclusion of minute radioactive crystals within the host crystal structure. The inclusions are typically zircon, apatite, or titanite which can accommodate uranium or thorium within their crystal structures (Faure 1986). One explanation is that the discolouration is caused by alpha particles emitted by the nuclei; the radius of the concentric shells are proportional to the particle's energy (Henderson & Bateson 1934).

Sodium polonide

Sodium polonide is a chemical compound with the formula Na2Po. It is a polonide, a set of very chemically stable compounds of polonium. Due to the difference in electronegativity (ΔEN) between sodium and polonium (≈ 1.1 under the Pauling system) and the slight non-metallic character of polonium, it is intermediate between intermetallic phases and ionic compounds.

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