View source for Polonium

{{Elementbox_header | number=84 | symbol=Po | name=polonium | left=[[bismuth]] | right=[[astatine]] | above=[[tellurium|Te]] | below=[[ununhexium|Uuh]] | color1=#cccc99 | color2=black }}
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{{Elementbox_density_gpcm3nrt | (beta) 9.398 }}
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{{Elementbox_heatcapacity_jpmolkat25 | 26.4 }}
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{{Elementbox_atomicradius_pm | [[1 E-10 m|190]] }}
{{Elementbox_atomicradiuscalc_pm | [[1 E-10 m|135]] }}
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{{Elementbox_cas_number | 7440-08-6 }}
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{{Elementbox_isotopes_decay | mn=210 | sym=Po
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'''Polonium''' is a [[chemical element]] in the [[periodic table]] that has the symbol '''Po''' and [[atomic number]] 84. A rare radioactive [[metalloid]], polonium is chemically similar to [[tellurium]] and [[bismuth]] and occurs in [[uranium]] ores. Polonium had been studied for possible use in heating [[spacecraft]].

== Notable characteristics ==
This radioactive substance dissolves readily in dilute [[acid]]s, but is only slightly [[solubility|soluble]] in [[alkali]]s.  It is closely related chemically to bismuth and tellurium. Polonium (in common with <sup>238</sup>Pu) has the ability to become airborne with ease. More than one hypothesis exists for how polonium does this;
one suggestion that that small clusters of polonium atoms are [[spallation|spalled off]] by the alpha decay. 

N. Momoshima, L.X. Song, S. Osaki and Y. Maeda, ''Environ Sci Technol''.  2001, '''35''', 2956-2960[http://www.medscape.com/medline/abstract/11478248?prt=true] report that [[microbe]]s can [[methylate]] polonium. They also claim that [[methylcobalamin]] can also methylate polonium.

Polonium has no stable isotopes and has over 50 potential isotopes. Polonium is extremely toxic and highly radioactive. Polonium has been found in [[tobacco smoke]] from tobacco leafs grown at some specific places, as a contaminant[http://www.webspawner.com/users/radioactivetobacco/index.html][http://kidslink.bo.cnr.it/besta/fumo/epolonio.html]and in uranium ores. All elements from polonium onward are significantly radioactive.

== Solid state form ==

[[Image:alpha po lattice.jpg|200px]]

The alpha form of the Po solid is cubic (Po-Po distance is 3.352 Å), it is a simple [[cubic (crystal system) | cubic]] solid which is not interpenetrated. A myth has grown up from a single sentence in one of the original papers on the crystal structure as determined by X-ray [[powder diffraction]]. Below is shown a diagram of a triple [[interpenetrate]]d cubic solid, while for Po this is not the structure a reasonable number of real examples of such an interlocking network have been found.

[[Image:interpenpomyth.jpg|400px]]

The beta form of polonium is hexagonal, it has been reported along with the alpha form several times in the chemical literature.

Two papers report X-ray [[diffraction]] experiments on Po metal.

R.J. Desando and R.C Lange, ''Journal of Inorganic and Nuclear Chemistry'', 1966, '''28''', 1837-1846.

W.H Beamer and C.R. Maxwell, ''Journal of Chemical Physics'', 1946, '''14''', 569-569 

The first report of the crystal strucutre of Po was done using [[electron diffraction]].

M.A. Rollier, S.B. Hendricks and L.R. Maxwell, ''Journal of Chemical Physics'', 1936, '''4''', 648-652.

== Applications ==
When it is mixed or [[alloy]]ed with [[beryllium]], polonium can be a [[neutron]] source.  Other uses;
*This element has also been used in devices that eliminate static charges in [[textile]] mills and other places. However, [[beta decay|beta]] sources are more commonly used and are less dangerous.
*Polonium is used on brushes that remove accumulated dust from [[photographic film]]s. The polonium in these brushes is sealed and controlled thus minimizing radiation hazards.

=== Polonium-210 === 

This isotope of polonium is an [[alpha decay|alpha emitter]] that has a half-life of 138.39 days. A milligram of polonium-210 emits as many alpha particles as 5 grams of [[radium]]. A great deal of energy is released by its decay with a half a gram quickly reaching a temperature above 750 K. A few [[curie]]s ([[Becquerel|gigabecquerels]]) of polonium-210 emit a blue glow which is caused by [[excitation]] of surrounding air. A single gram of polonium-210 generates 140 watts of heat energy. Since nearly all [[alpha radiation]] can be easily stopped by ordinary containers and upon hitting its surface releases its energy, polonium-210 has been used as a lightweight heat source to power thermoelectric cells in [[artificial satellite]]s. A polonium-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.
Because of its short halflife though polonium-210 cannot provide power for long-term space missions and has been phased out of use in this application.

== History ==
Also called Radium F, polonium was discovered by [[Maria Skłodowska-Curie]] and her husband [[Pierre Curie]] in [[1898]] and was later named after Marie's home land of [[Poland]] (Latin: ''Polonia''). Poland at the time was under Russian, Prussian and Austrian [[Partitions of Poland|domination]], and not recognized as an independent country. It was Marie's hope that naming the element after her home land would add notoriety to its plight.  Polonium may be the first element named to highlight a political controversy.

This element was the first one discovered by the Curies while they were investigating the cause of [[uraninite|pitchblende]] [[radioactivity]]. The pitchblende, after removal of uranium and radium, was more radioactive than both radium and uranium put together. This spurred them on to find the element. The electroscope showed it separating with bismuth.

== Occurrence ==
A very rare element in nature, polonium is found in [[uranium]] ores at about 100 [[microgram]]s per [[metric ton]] (1:10<sup>10</sup>). Its natural abundance is approximately 0.2% of radium's.

In [[1934]] an experiment showed that when natural [[bismuth]]-209 is bombarded with [[neutron]]s, bismuth-210, which is the parent of polonium, was created. Polonium may now be made in milligram amounts in this procedure which uses high neutron fluxes found in [[nuclear reactor]]s.

== Isotopes ==
Polonium has many [[isotope]]s all of which are [[radioactivity|radioactive]]. There are 25 known isotopes of polonium with [[atomic mass]]es that range from 194 u to 218 u. Polonium-210 is the most widely available. Polonium-209 ([[half-life]] 103 years) and polonium-208 (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of [[lead]] or [[bismuth]] in a [[cyclotron]]. However these isotopes are expensive to produce.

The great radioactivity of polonium and its immediate neighbors to the right on the periodic table, and its stark contrast with [[lead]] and [[bismuth]], is due to the great instability of nuclei containing 84 or more protons. Nuclei that contain 128 neutrons along with 84 or more protons are especially unstable. Curiously, [[thorium]]-232 and [[uranium]]-238 are in an "island of stability" which renders them stable enough to be found in large quantities in nature, but heavier nuclei are more and more affected by [[spontaneous fission]].

== Precautions ==
Polonium is a highly radioactive and toxic element and is dangerous to handle.
Even in [[milligram]] or [[microgram]] amounts, handling polonium-210 is very dangerous and requires special equipment used with strict procedures. Direct damage occurs from energy absorption into tissues from alpha particles.

The maximum allowable body burden for ingested polonium is only 1100 [[becquerels]] (0.03 microcurie), which is equivalent to a particle weighing only 6.8 &times; 10<sup>-12</sup> gram. Weight for weight polonium is approximately 2.5 &times; 10<sup>11</sup> times as toxic as [[hydrocyanic acid]]. The maximum permissible concentration for airborne soluble polonium compounds is about 7,500 Bq/m³ (2 &times; 10<sup>-11</sup> µCi/cm³).

== References ==
*[http://periodic.lanl.gov/elements/84.html Los Alamos National Laboratory &ndash; Polonium]

== External links ==
{{Commons|Polonium}}
{{wiktionary|polonium}}
*[http://www.webelements.com/webelements/elements/text/Po/index.html WebElements.com &ndash; Polonium]
*[http://www.globalsecurity.org/wmd/intro/polonium.htm History of Polonium]

[[Category:Chemical elements]]
[[Category:Metalloids]]
[[Category:Chalcogens]]
[[Category:Chemistry Workgroup]]

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