Polonium is achemical element; it hassymbolPo andatomic number 84. A rare and highlyradioactivemetal (although sometimes classified as ametalloid) with no stableisotopes, polonium is achalcogen and chemically similar toselenium andtellurium, though its metallic character resembles that of itshorizontal neighbors in theperiodic table:thallium,lead, andbismuth. Due to the shorthalf-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleetingpolonium-210 (with a half-life of 138 days) inuraniumores, as it is thepenultimate daughter of naturaluranium-238. Though two longer-lived isotopes exist (polonium-209 with a half-life of 124 years and polonium-208 with a half-life of 2.898 years), they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by theneutron irradiation ofbismuth. Due to its intense radioactivity, which results in theradiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.
Polonium was discovered on 18 July 1898 byMarie Skłodowska-Curie andPierre Curie, when it was extracted from the uranium orepitchblende[4] and identified solely by its strong radioactivity: it was the first element to be discovered in this way.[5] Polonium was named after Marie Skłodowska-Curie's homeland of Poland, which at the time waspartitioned between three countries. Polonium has few applications, and those are related to its radioactivity: heaters inspace probes,antistatic devices, sources ofneutrons andalpha particles, andpoison (e.g.,poisoning of Alexander Litvinenko). It is extremely dangerous to humans.
210Po is analpha emitter that has a half-life of 138.4 days; it decays directly to its stabledaughter isotope,206Pb. A milligram (5 curies) of210Po emits about as many alpha particles per second as 5 grams of226Ra,[6] which means it is 5,000 times more radioactive than radium. A fewcuries (1 curie equals 37 gigabecquerels, 1 Ci = 37 GBq) of210Po emit a blue glow which is caused byionisation of the surrounding air.
About one in 100,000 alpha emissions causes an excitation in the nucleus which then results in the emission of agamma ray with a maximum energy of 803 keV.[7][8]
210Po has the abilityto 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 formdiatomic Po2 molecules, even though the melting point of polonium is 254 °C (489 °F) and its boiling point is 962 °C (1,764 °F).[15][16][1]More than one hypothesis exists for how polonium does this; one suggestion is that small clusters of polonium atoms arespalled off by the alpha decay.[17]
The chemistry of polonium is similar to that oftellurium, although it also shows some similarities to its neighborbismuth due to its metallic character. Polonium dissolves readily in diluteacids but is only slightlysoluble inalkalis. Poloniumsolutions 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+. As polonium also emits alpha-particles after disintegration so this process is accompanied by bubbling and emission of heat and light byglassware due to the absorbed alpha particles; as a result, polonium solutions are volatile and will evaporate within days unless sealed.[18][19] At pH about 1, polonium ions are readily hydrolyzed and complexed by acids such asoxalic acid,citric acid, andtartaric acid.[20]
Polonium has no common compounds, and almost all of its compounds are synthetically created; more than 50 of those are known.[21] The most stable class of polonium compounds arepolonides, which are prepared by direct reaction of two elements.Na2Po has theantifluorite structure, the polonides ofCa,Ba,Hg, Pb and lanthanides form a NaCl lattice,BePo andCdPo have thewurtzite andMgPo thenickel arsenide structure. Most polonides decompose upon heating to about 600 °C, except for HgPo that decomposes at ~300 °C and thelanthanide polonides, which do not decompose but melt at temperatures above 1000 °C. For example, the polonide ofpraseodymium (PrPo) melts at 1250 °C, and that ofthulium (TmPo) melts at 2200 °C.[22]PbPo is one of the very few naturally occurring polonium compounds, as poloniumalpha decays to formlead.[23]
Polonium hydride (PoH 2) is a volatile liquid at room temperature prone to dissociation; it is thermally unstable.[22]Water is the only other knownhydrogen chalcogenide which is a liquid at room temperature; however, this is due to hydrogen bonding. The three oxides,PoO,PoO2 andPoO3, are the products of oxidation of polonium.[24]
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.[25] 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.[26]
A limitedorganopolonium chemistry is known, mostly restricted to dialkyl and diaryl polonides (R2Po), triarylpolonium halides (Ar3PoX), and diarylpolonium dihalides (Ar2PoX2).[28][29] Polonium also forms soluble compounds with someligands, such as2,3-butanediol andthiourea.[28]
Polonium has 42 known isotopes, all of which areradioactive. They haveatomic masses that range from 186 to 227u.210Po (half-life 138.376 days) is the most widely available and is manufactured via neutron capture by naturalbismuth. It also naturally occurs as a trace in uranium ores, as it is the penultimate member of the decay chain of238U. The longer-lived209Po (half-life 124 years, longest-lived of all polonium isotopes)[3] and208Po (half-life 2.9 years) can be manufactured through the alpha, proton, or deuteron bombardment oflead or bismuth in acyclotron.[35]
Tentatively called "radium F", polonium was discovered byMarie and Pierre Curie in July 1898,[36][37] and was named after Marie Curie's native land ofPoland (Latin:Polonia).[38][39] Poland at the time was underRussian,German, andAustro-Hungarianpartition, 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. Polonium may be the first element named to highlight a political controversy.[40]
This element was the first one discovered by the Curies while they were investigating the cause ofpitchblenderadioactivity. Pitchblende, after removal of the radioactive elementsuranium andthorium, 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 isolatedradium.[18][36][41] German scientistWilly 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.[42][43]
In the United States, polonium was produced as part of theManhattan Project'sDayton Project duringWorld War II. Polonium andberyllium were the key ingredients of the 'Urchin' initiator at the center of the bomb's sphericalpit.[44] 'Urchin' initiated thenuclear chain reaction at the moment ofprompt-criticality to ensure that the weapon did notfizzle. 'Urchin' was used in early U.S. weapons; subsequent U.S. weapons utilized a pulse neutron generator for the same purpose.[44]
Much of the basic physics of polonium wasclassified until after the war. The fact that a polonium-beryllium (Po-Be) initiator was used in the gun-type nuclear weapons was classified until the 1960s.[45]
Polonium is a very rare element in nature because of the shorthalf-lives of all its isotopes. Nine isotopes, from 210 to 218 inclusive, occur intraces asdecay products:210Po,214Po, and218Po occur in thedecay chain of238U;211Po and215Po occur in the decay chain of235U;212Po and216Po occur in the decay chain of232Th; and213Po and217Po occur in the decay chain of237Np. (No primordial237Np survives, but traces of it are continuously regenerated through (n,2n) knockout reactions in natural238U.)[49] Of these,210Po is the only isotope with a half-life longer than 3 minutes.[50]
Polonium can be found inuranium ores at about 0.1 mg permetric ton (1 part in 1010),[51][52] which is approximately 0.2% of the abundance of radium. The amounts in the Earth's crust are not harmful. Polonium has been found intobacco smoke from tobacco leaves grown withphosphate fertilizers.[53][54][55]
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) ofpolonium-210 and was obtained by processing 37 tonnes of residues from radium production.[56] Polonium is now usually obtained by irradiating bismuth with high-energy neutrons or protons.[18][57]
In 1934, an experiment showed that when natural209Bi is bombarded withneutrons,210Bi is created, which then decays to210Po via beta-minus decay. By irradiating certain bismuth salts containing light element nuclei such as beryllium, a cascading (α,n) reaction can also be induced to produce210Po in large quantities.[58] The final purification is done pyrochemically followed by liquid-liquid extraction techniques.[59] Polonium may now be made in milligram amounts in this procedure which uses high neutron fluxes found innuclear reactors.[57] Only about 100 grams are produced each year, practically all of it in Russia, making polonium exceedingly rare.[60][61]
The longer-lived isotopes of polonium,208Po and209Po, can be formed byproton ordeuteron bombardment of bismuth using acyclotron. Other more neutron-deficient and more unstable isotopes can be formed by the irradiation of platinum withcarbon nuclei.[64]
Polonium-based sources of alpha particles were produced in the formerSoviet Union.[65] Such sources were applied for measuring the thickness of industrial coatings via attenuation of alpha radiation.[66]
Because of intense alpha radiation, a one-gram sample of210Po 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 powerradioisotope thermoelectric generators viathermoelectric materials.[6][18][67][68] For example,210Po heat sources were used in theLunokhod 1 (1970) and Lunokhod 2 (1973)Moon rovers to keep their internal components warm during the lunar nights, as well as theKosmos 84 and 90 satellites (1965).[65][69]
The alpha particles emitted by polonium can be converted to neutrons using beryllium oxide, at a rate of 93 neutrons per million alpha particles.[67] Po-BeO mixtures are used as passiveneutron sources with agamma-ray-to-neutron production ratio of 1.13 ± 0.05, lower than fornuclear fission-based neutron sources.[70] Examples of Po-BeO mixtures oralloys used as neutron sources are aneutron trigger or initiator fornuclear weapons[18][71] and for inspections of oil wells. About 1500 sources of this type, with an individual activity of 1,850 Ci (68 TBq), had been used annually in the Soviet Union.[72]
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.[73] Alpha particles emitted by polonium ionize air molecules that neutralize charges on the nearby surfaces.[74][75] Some anti-static brushes contain up to 500 microcuries (20 MBq) of210Po as a source of charged particles for neutralizing static electricity.[76] In the US, devices with no more than 500 μCi (19 MBq) of (sealed)210Po per unit can be bought in any amount under a "general license",[77] 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 dangerousbeta particle sources.[6]
Tiny amounts of210Po 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 of210Po 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 thealpha radiation (used in experiments such as cloud chambers) to pass while preventing the polonium from being released and presenting a toxic hazard.[citation needed]
Poloniumspark plugs were marketed byFirestone 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 asAlfred Matthew Hubbard's prototyperadium 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.)[78][79]
Polonium can be hazardous and has no biological role.[18] By mass, polonium-210 is around 250,000 times more toxic thanhydrogen cyanide (theLD50 for210Po is less than 1microgram for an average adult (see below) compared with about 250milligrams for hydrogen cyanide[80]). The main hazard is its intense radioactivity (as an alpha emitter), which makes it difficult to handle safely. Even inmicrogram amounts, handling210Po is extremely dangerous, requiring specialized equipment (a negative pressure alphaglove 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 theepidermis and hence are not hazardous as long as the alpha particles remain outside the body and do not come near the eyes, which are living tissue. Wearing chemically resistant and intact gloves is a mandatory precaution to avoid transcutaneousdiffusion of polonium directly through theskin. Polonium delivered in concentratednitric acid can easily diffuse through inadequate gloves (e.g.,latex gloves) or the acid may damage the gloves.[81]
Polonium does not have toxic chemical properties.[82]
It has been reported that somemicrobes canmethylate polonium by the action ofmethylcobalamin.[83][84] This is similar to the way in whichmercury,selenium, andtellurium are methylated in living things to createorganometallic 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.[85]
Themedian lethal dose (LD50) for acute radiation exposure is about 4.5 Sv.[86] Thecommitted effective dose equivalent210Po is 0.51 μSv/Bq if ingested, and 2.5 μSv/Bq if inhaled.[87] 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 of210Po could thus in theory poison 20 million people, of whom 10 million would die. The actual toxicity of210Po is lower than these estimates because radiation exposure that is spread out over several weeks (thebiological half-life of polonium in humans is 30 to 50 days[88]) is somewhat less damaging than an instantaneous dose. It has been estimated that amedian lethal dose of210Po is 15 megabecquerels (0.41 mCi), or 0.089 micrograms (μg), still an extremely small amount.[89][90] For comparison, one grain oftable salt is about 0.06 mg = 60 μg.[91]
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.[86] The general population is exposed to small amounts of polonium as aradon daughter in indoor air; the isotopes214Po and218Po are thought to cause the majority[92] of the estimated 15,000–22,000 lung cancer deaths in the US every year that have been attributed to indoor radon.[93]Tobacco smoking causes additional exposure to polonium.[94]
The maximum allowable body burden for ingested210Po is only 1.1 kBq (30 nCi), which is equivalent to a particle massing only 6.8 picograms.[95] The maximum permissible workplace concentration of airborne210Po is about 10 Bq/m3 (3×10−10 μCi/cm3).[96] The target organs for polonium in humans are thespleen andliver.[97] 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 ascaesium ortritium (as T2O).[98][99]
210Po is widely used in industry, and readily available with little regulation or restriction.[100][101] 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)."[100] 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.[citation needed]
Polonium and its compounds must be handled with caution inside special alphaglove boxes, equipped withHEPA filters and continuously maintained under depression to prevent the radioactive materials from leaking out. Gloves made ofnatural rubber (latex) do not properly withstand chemical attacks, a.o. by concentratednitric acid(e.g., 6 MHNO3) commonly used to keep polonium insolution while minimizing itssorption onto glass. They do not provide sufficient protection against the contamination from polonium (diffusion of210Po solution through the intact latex membrane, or worse, direct contact through tiny holes and cracks produced when the latex begins to suffer degradation by acids or UV from ambient light); additional surgical gloves are necessary (inside the glovebox to protect the main gloves when handling strong acids and bases, and also from outside to protect the operator hands against210Po contamination from diffusion, or direct contact through glove defects). Chemically more resistant, and also denser,neoprene and butyl gloves shield alpha particles emitted by polonium better than natural rubber.[102] The use of natural rubber gloves is not recommended for handling210Po solutions.
Despite the element's highly hazardous properties, circumstances in which polonium poisoning can occur are rare. Its extreme scarcity in nature,[103] the short half-lives of all its isotopes, the specialised facilities and equipment needed to obtain any significant quantity, and safety precautions against laboratory accidents all make harmful exposure events unlikely. As such, only a handful of cases of radiation poisoning specifically attributable to polonium exposure have been confirmed.[104]
In response to concerns about the risks of occupational polonium exposure, quantities of210Po were administered to five human volunteers at the University of Rochester from 1944 to 1947, in order to study its biological behaviour. These studies were funded by theManhattan Project and the AEC. Four men and a woman participated, all suffering from terminal cancers, and ranged in age from their early thirties to early forties; all were chosen because experimenters wanted subjects who had not been exposed to polonium either through work or accident.[105]210Po was injected into four hospitalised patients, and orally given to a fifth. None of the administered doses (all ranging from 0.17 to 0.30 μCi kg−1) approached fatal quantities.[106][105]
The first documented death directly resulting from polonium poisoning occurred in theSoviet Union, on 10 July 1954.[107][108] An unidentified 41-year-old man presented for medical treatment on 29 June, with severe vomiting and fever; the previous day, he had been working for five hours in an area in which, unknown to him, a capsule containing210Po had depressurised and begun to disperse in aerosol form. Over this period, his total intake of airborne210Po was estimated at 0.11 GBq (almost 25 times the estimated LD50 by inhalation of 4.5 MBq). Despite treatment, his condition continued to worsen and he died 13 days after the exposure event.[107]
From 1955 to 1957 theWindscale Piles had been releasing polonium-210. TheWindscale fire brought the need for testing of the land downwind for radioactive material contamination, and this is how it was found. An estimate of 8.8 terabecquerels (240 Ci) of polonium-210 has been made.
It has also been suggested thatIrène Joliot-Curie's 1956 death from leukaemia was owed to the radiation effects of polonium. She was accidentally exposed in 1946 when a sealed capsule of the element exploded on her laboratory bench.[109]
As well, several deaths in Israel during 1957–1969 have been alleged to have resulted from210Po exposure.[110] A leak was discovered at aWeizmann Institute laboratory in 1957. Traces of210Po 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, one of his students, and two colleagues died from variouscancers over the subsequent few years. The issue was investigated secretly, but there was never any formal admission of a connection between the leak and the deaths.[111]
TheChurch Rock uranium mill spill 16 July 1979 is reported to have releasedpolonium-210. The report states animals had higher concentrations of lead-210, polonium-210 and radium-226 than the tissues from control animals.[112]
The cause of the2006 death ofAlexander Litvinenko, a former RussianFSB agent who had defected to the United Kingdom in 2001, was identified to be poisoning with a lethal dose of210Po;[113][114] it was subsequently determined that the210Po had probably been deliberately administered to him by two Russian ex-security agents,Andrey Lugovoy andDmitry Kovtun.[115][116] As such, Litvinenko's death was the first (and, to date, only) confirmed instance in which polonium's extreme toxicity has been used with malicious intent.[117][118][119]
In 2011, an allegation surfaced that the death ofPalestinian leaderYasser Arafat, who died on 11 November 2004 of uncertain causes, also resulted from deliberate polonium poisoning,[120][121] and in July 2012, concentrations of210Po many times more than normal were detected in Arafat's clothes and personal belongings by the Institut de Radiophysique in Lausanne, Switzerland.[122][123] Even though Arafat's symptoms were acute gastroenteritis with diarrhoea and vomiting,[124] the institute's spokesman said that despite the tests the symptoms described in Arafat's medical reports were not consistent with210Po poisoning, and conclusions could not be drawn.[123] In 2013 the team found levels of polonium in Arafat's ribs and pelvis 18 to 36 times the average,[125][126] even though by this point in time the amount had diminished by a factor of 2 million.[127] Forensic scientist Dave Barclay stated, "In my opinion, it is absolutely certain that the cause of his illness was polonium poisoning. ... What we have got is the smoking gun - the thing that caused his illness and was given to him with malice."[124][125] Subsequently, French and Russian teams claimed that the elevated210Po levels were not the result of deliberate poisoning, and did not cause Arafat's death.[128][129]
It has also been suspected that Russian businessmanRoman Tsepov was killed with polonium. He had symptoms similar to Aleksander Litvinenko.[130]
It has been suggested thatchelation agents, such as British anti-Lewisite (dimercaprol), can be used to decontaminate humans.[131] In one experiment, rats were given a fatal dose of 1.45 MBq/kg (8.7 ng/kg) of210Po;all untreated rats were dead after 44 days, but 90% of the rats treated with the chelation agentHOEtTTC remained alive for five months.[132]
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.[133]
Polonium-210 is widespread in thebiosphere, including in human tissues, because of its position in theuranium-238 decay chain. Naturaluranium-238 in theEarth's crust decays through a series of solid radioactive intermediates includingradium-226 to the radioactive noble gasradon-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 stablelead-206.[134][135][136]
As early as the 1920s, French biologistAntoine Lacassagne, using polonium provided by his colleagueMarie Curie, showed that the element has a specific pattern of uptake in rabbit tissues, with high concentrations, particularly inliver,kidney, andtestes.[137] 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[138] and that similar patterns of distribution occur in human tissues.[139] 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.[140]
Polonium-210 in tobacco contributes to many of the cases oflung cancer worldwide. Most of this polonium is derived fromlead-210 deposited on tobacco leaves from the atmosphere; the lead-210 is a product ofradon-222 gas, much of which appears to originate from the decay ofradium-226 from fertilizers applied to the tobacco soils.[55][141][142][143][144]
The presence of polonium in tobacco smoke has been known since the early 1960s.[145][146] 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.[55]
^abThayer, John S. (2010). "Relativistic Effects and the Chemistry of the Heavier Main Group Elements".Relativistic Methods for Chemists. Challenges and Advances in Computational Chemistry and Physics.10: 78.doi:10.1007/978-1-4020-9975-5_2.ISBN978-1-4020-9974-8.
^Desando, R. J.; Lange, R. C. (1966). "The structures of polonium and its compounds—I α and β polonium metal".Journal of Inorganic and Nuclear Chemistry.28 (9):1837–1846.doi:10.1016/0022-1902(66)80270-1.
^abBagnall, K. W.; d'Eye, R. W. M.; Freeman, J. H. (1955). "The polonium halides. Part I. Polonium chlorides".Journal of the Chemical Society (Resumed):2320–2326.doi:10.1039/JR9550002320.
^abBagnall, K. W.; d'Eye, R. W. M.; Freeman, J. H. (1955). "The polonium halides. Part II. Bromides".Journal of the Chemical Society (Resumed):3959–3963.doi:10.1039/JR9550003959.
^Bagnall, K. W.; d'Eye, R. W. M.; Freeman, J. H. (1956). "657. The polonium halides. Part III. Polonium tetraiodide".Journal of the Chemical Society (Resumed):3385–3389.doi:10.1039/JR9560003385.
^Emsley, John (2011).Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. p. 415.ISBN978-0-19-960563-7.
^Pfützner, M. (1999). "Borders of the Nuclear World – 100 Years After Discovery of Polonium".Acta Physica Polonica B.30 (5): 1197.Bibcode:1999AcPPB..30.1197P.
^"Studies of polonium metabolism in human subjects", Chapter 3 inBiological Studies with Polonium, Radium, and Plutonium, National, Nuclear Energy Series, Volume VI-3, McGraw-Hill, New York, 1950, cited in "American Nuclear Guinea Pigs ...", 1986 House Energy and Commerce committee report
^Schulz, Wallace W.; Schiefelbein, Gary F.; Bruns, Lester E. (1969). "Pyrochemical Extraction of Polonium from Irradiated Bismuth Metal".Ind. Eng. Chem. Process Des. Dev.8 (4):508–515.doi:10.1021/i260032a013.
^"Q&A: Polonium-210". RSC Chemistry World. 27 November 2006. Retrieved12 January 2009.
^Usanov, V. I.; Pankratov, D. V.; Popov, É. P.; Markelov, P. I.; Ryabaya, L. D.; Zabrodskaya, S. V. (1999). "Long-lived radionuclides of sodium, lead-bismuth, and lead coolants in fast-neutron reactors".Atomic Energy.87 (3):658–662.doi:10.1007/BF02673579.S2CID94738113.
^Momoshima, N.; Song, L. X.; Osaki, S.; Maeda, Y. (2001). "Formation and emission of volatile polonium compound by microbial activity and polonium methylation with methylcobalamin".Environ Sci Technol.35 (15):2956–2960.Bibcode:2001EnST...35.2956M.doi:10.1021/es001730.PMID11478248.
^Harrison, J.; Leggett, Rich; Lloyd, David; Phipps, Alan; et al. (2007). "Polonium-210 as a poison".J. Radiol. Prot.27 (1):17–40.Bibcode:2007JRP....27...17H.doi:10.1088/0952-4746/27/1/001.PMID17341802.S2CID27764788.The conclusion is reached that 0.1–0.3 GBq or more absorbed to blood of an adult male is likely to be fatal within 1 month. This corresponds to ingestion of 1–3 GBq or more, assuming 10% absorption to blood
^Fink, Robert (1950).Biological studies with polonium, radium, and plutonium. National Nuclear Energy Series (in Russian). Vol. VI-3. McGraw-Hill.ISBN5-86656-114-X.
^abGasteva, G. N. (2001). "Ostraja lučevaja boleznʹ ot postuplenija v organizm polonija" [Acute radiation sickness by ingestion of polonium into the body]. In Ilʹin, L. A. (ed.).Radiacionnaja medicina: rukovodstvo dlja vračej-issledovatelej i organizatorov zdravooxranenija, Tom 2 (Radiacionnye poraženija čeloveka) [Radiation medicine: a guide for medical researchers and healthcare managers, Volume 2 (Radiation damage to humans)] (in Russian). IzdAT. pp. 99–107.ISBN5-86656-114-X.
^Froidevaux, P.; Baechler, S. B.; Bailat, C. J.; Castella, V.; Augsburger, M.; Michaud, K.; Mangin, P.; Bochud, F. O. O. (2013). "Improving forensic investigation for polonium poisoning".The Lancet.382 (9900): 1308.doi:10.1016/S0140-6736(13)61834-6.PMID24120205.S2CID32134286.
^Rencováa J.; Svoboda V.; Holuša R.; Volf V.; et al. (1997). "Reduction of subacute lethal radiotoxicity of polonium-210 in rats by chelating agents".International Journal of Radiation Biology.72 (3):341–8.doi:10.1080/095530097143338.PMID9298114.
^Martell, E. A. (1975). "Tobacco Radioactivity and Cancer in Smokers: Alpha interactions with chromosomes of cells surrounding insoluble radioactive smoke particles may cause cancer and contribute to early atherosclerosis development in cigarette smokers".American Scientist.63 (4):404–412.Bibcode:1975AmSci..63..404M.JSTOR27845575.PMID1137236.
_NIST_ASD_emission_spectrum.png)
