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= Polonium =
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Introduction
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Polonium is a chemical element; it has symbol Po and atomic number 84.
A rare and highly radioactive metal (although sometimes classified as
a metalloid) with no stable isotopes, polonium is a chalcogen and
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 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 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 on 18 July 1898 by Marie Skłodowska-Curie and
Pierre Curie, when it was extracted from the uranium ore pitchblende
and identified solely by its strong radioactivity: it was the first
element to be discovered in this way. Polonium was named after Marie
Skłodowska-Curie's homeland of Poland, which at the time was
partitioned between three countries. Polonium has few applications,
and those are related to its radioactivity: heaters in space probes,
antistatic devices, sources of neutrons and alpha particles, and
poison (e.g., poisoning of Alexander Litvinenko). It is extremely
dangerous to humans.
Characteristics
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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, which means it is 5,000 times more radioactive than
radium. 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.
Solid state form
==================
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 (space group Pmm, no.
221). The unit cell has an edge length of 335.2 picometers; the beta
form is rhombohedral. The structure of polonium has been characterized
by X-ray diffraction and electron diffraction.
210Po has the ability to become airborne with ease: if a sample is
heated in air to 55 C, 50% of it is vaporized in 45 hours to form
diatomic Po2 molecules, even though the melting point of polonium is
254 C and its boiling point is 962 C.
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+. As polonium also emits alpha-particles after disintegration,
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. At pH about 1, polonium ions are readily hydrolyzed and
complexed by acids such as oxalic acid, citric acid, and tartaric
acid.
Compounds
===========
Polonium has no common compounds, and almost all of its compounds are
synthetically created; more than 50 of those are known. 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, the polonide of praseodymium (PrPo) melts at 1250 °C,
and that of thulium (TmPo) melts at 2200 °C. PbPo is one of the very
few naturally occurring polonium compounds, as polonium alpha decays
to form lead.
Polonium hydride () is a volatile liquid at room temperature prone to
dissociation; it is thermally unstable. Water is the only other known
hydrogen chalcogenide which is a liquid at room temperature; however,
this is due to hydrogen bonding. The three oxides, PoO, PoO2 and PoO3,
are the products of oxidation of polonium.
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. 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.
Other polonium compounds include the polonite, potassium polonite;
various polonate solutions; and the acetate, bromate, carbonate,
citrate, chromate, cyanide, formate, (II) or (IV) hydroxide, nitrate,
selenate, selenite, monosulfide, sulfate, disulfate or sulfite salts.
A limited organopolonium chemistry is known, mostly restricted to
dialkyl and diaryl polonides (R2Po), triarylpolonium halides (Ar3PoX),
and diarylpolonium dihalides (Ar2PoX2). Polonium also forms soluble
compounds with some ligands, such as 2,3-butanediol and thiourea.
Polonium compounds
!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
|PoO black
|PoO2 pale yellow 500 (dec.) 885 fcc cF12 Fmm 225 563.7 563.7
563.7 4 8.94
|PoH2 -35.5
|PoCl2 dark ruby red 355 130 orthorhombic oP3 Pmmm 47 367 435
450 1 6.47
|PoBr2 purple-brown 270 (dec.)
|PoCl4 yellow 300 200 monoclinic
|PoBr4 red 330 (dec.) fcc cF100 Fmm 225 560 560 560 4
|PoI4 black
Oxides
* PoO
* PoO2
* PoO3
Hydrides
* PoH2
Halides
* PoX2 (except PoF2)
* PoX4
* PoF6
* PoBr2Cl2 (salmon pink)
Isotopes
==========
Polonium has 42 known isotopes, all of which are radioactive. They
have atomic masses that range from . 210Po (half-life 138.376 days) is
the most widely available and is manufactured via neutron capture by
natural bismuth. It also naturally occurs as a trace in uranium ores,
as it is the penultimate member of the decay chain of 238U. The
longer-lived 209Po (half-life 124 years, longest-lived of all polonium
isotopes) and 208Po (half-life 2.9 years) can be manufactured through
the alpha, proton, or deuteron bombardment of lead or bismuth in a
cyclotron.
History
======================================================================
Tentatively called "radium F", polonium was discovered by Marie and
Pierre Curie in July 1898, and was named after Marie Curie's native
land of Poland ().
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. 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 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. 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.
In the United States, polonium was produced as part of the Manhattan
Project's Dayton Project during World War II. Polonium and beryllium
were the key ingredients of the 'Urchin' initiator at the center of
the bomb's spherical pit. 'Urchin' initiated the nuclear chain
reaction at the moment of prompt-criticality to ensure that the weapon
did not fizzle. 'Urchin' was used in early U.S. weapons; subsequent
U.S. weapons utilized a pulse neutron generator for the same purpose.
Much of the basic physics of polonium was classified 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.
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 of polonium to study its excretion.
Occurrence and production
======================================================================
Polonium is a very rare element in nature because of the short
half-lives of all its isotopes. Nine isotopes, from 210 to 218
inclusive, occur in traces as decay products: 210Po, 214Po, and 218Po
occur in the decay chain of 238U; 211Po and 215Po occur in the decay
chain of 235U; 212Po and 216Po occur in the decay chain of 232Th; and
213Po and 217Po occur in the decay chain of 237Np. (No primordial
237Np survives, but traces of it are continuously regenerated through
(n,2n) knockout reactions in natural 238U.) Of these, 210Po is the
only isotope with a half-life longer than 3 minutes.
Polonium can be found in uranium ores at about 0.1 mg per metric ton
(1 part in 1010), 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.
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 (9 mg) of polonium-210 and was obtained
by processing 37 tonnes of residues from radium production. Polonium
is now usually obtained by irradiating bismuth with high-energy
neutrons or protons.
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. By irradiating certain bismuth salts containing
light element nuclei such as beryllium, a cascading (α,n) reaction can
also be induced to produce 210Po in large quantities. The final
purification is done pyrochemically followed by liquid-liquid
extraction techniques. 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, practically all
of it in Russia, making polonium exceedingly rare.
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.
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-deficient and more unstable isotopes can be formed by the
irradiation of platinum with carbon nuclei.
Applications
======================================================================
Polonium-based sources of alpha particles were produced in the former
Soviet Union. Such sources were applied for measuring the thickness of
industrial coatings via attenuation of alpha radiation.
Because of intense alpha radiation, a one-gram sample of 210Po will
spontaneously heat up to above 500 C generating about 140 watts of
power. Therefore, 210Po is used as an atomic heat source to power
radioisotope thermoelectric generators via thermoelectric materials.
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).
The alpha particles emitted by polonium can be converted to neutrons
using beryllium oxide, at a rate of 93 neutrons per million alpha
particles. Po-BeO mixtures are used as passive neutron sources with a
gamma-ray-to-neutron production ratio of 1.13 ± 0.05, lower than for
nuclear fission-based neutron sources. Examples of Po-BeO mixtures or
alloys used as neutron sources are a neutron trigger or initiator for
nuclear weapons and for inspections of oil wells. About 1500 sources
of this type, with an individual activity of 1850 Ci, had been used
annually in the Soviet Union.
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. Alpha particles emitted by polonium ionize
air molecules that neutralize charges on the nearby surfaces. Some
anti-static brushes contain up to 500 uCi of 210Po as a source of
charged particles for neutralizing static electricity. In the US,
devices with no more than 500 μCi of (sealed) 210Po per unit can be
bought in any amount under a "general license", 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.
Tiny amounts of 210Po are sometimes used in the laboratory and for
teaching purposes--typically of the order of 4 -, 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.
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.)
Overview
==========
Polonium can be hazardous and has no biological role. By mass,
polonium-210 is around 250,000 times more toxic than hydrogen cyanide
(the 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 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 and
do not come near the eyes, which are living tissue. 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.
Polonium does not have toxic chemical properties.
It has been reported that some microbes can methylate polonium by the
action of methylcobalamin.
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.
Acute effects
===============
The median lethal dose (LD50) for acute radiation exposure is about
4.5 Sv. The committed effective dose equivalent 210Po is 0.51 μSv/Bq
if ingested, and 2.5 μSv/Bq if inhaled. A fatal 4.5 Sv dose can be
caused by ingesting 8.8 MBq, about 50 nanograms (ng), or inhaling 1.8
MBq, 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) is somewhat less damaging than an
instantaneous dose. It has been estimated that a median lethal dose of
210Po is 15 MBq, or 0.089 micrograms (μg), still an extremely small
amount. For comparison, one grain of table salt is about 0.06 mg = 60
μg.
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 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.
Regulatory exposure limits and handling
=========================================
The maximum allowable body burden for ingested 210Po is only 1.1 kBq,
which is equivalent to a particle massing only 6.8 picograms. The
maximum permissible workplace concentration of airborne 210Po is about
10 Bq/m3 ( μCi/cm3). The target organs for polonium in humans are the
spleen and liver. 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 Ci 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 Ci." 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 with caution inside special
alpha glove boxes, equipped with HEPA filters and continuously
maintained under depression to prevent the radioactive materials from
leaking out. Gloves made of natural rubber (latex) do not properly
withstand chemical attacks, a.o. by concentrated nitric acid commonly
used to keep polonium in solution while minimizing its sorption onto
glass. They do not provide sufficient protection against the
contamination from polonium (diffusion of 210Po 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
against 210Po 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. The use of natural rubber gloves is not
recommended for handling 210Po solutions.
Cases of poisoning
====================
Despite the element's highly hazardous properties, circumstances in
which polonium poisoning can occur are rare. Its extreme scarcity in
nature, 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.
20th century
==============
In response to concerns about the risks of occupational polonium
exposure, quantities of 210Po 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 the
Manhattan 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. 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.
The first documented death directly resulting from polonium poisoning
occurred in the Soviet Union, on 10 July 1954. 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 containing
210Po had depressurised and begun to disperse in aerosol form. Over
this period, his total intake of airborne 210Po 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.
From 1955 to 1957 the Windscale Piles had been releasing polonium-210.
The Windscale 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 that Irène 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.
As well, several deaths in Israel during 1957-1969 have been alleged
to have resulted from 210Po exposure. 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, one of his students, and two
colleagues died from various cancers 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.
The Church Rock uranium mill spill 16 July 1979 is reported to have
released polonium-210. The report states animals had higher
concentrations of lead-210, polonium-210 and radium-226 than the
tissues from control animals.
21st century
==============
The cause of the 2006 death of Alexander Litvinenko, a former Russian
FSB agent who had defected to the United Kingdom in 2001, was
identified to be poisoning with a lethal dose of 210Po; it was
subsequently determined that the 210Po had probably been deliberately
administered to him by two Russian ex-security agents, Andrey Lugovoy
and Dmitry Kovtun. 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.
In 2011, an allegation surfaced that the death of Palestinian leader
Yasser Arafat, who died on 11 November 2004 of uncertain causes, also
resulted from deliberate polonium poisoning, and in July 2012,
concentrations of 210Po many times more than normal were detected in
Arafat's clothes and personal belongings by the Institut de
Radiophysique in Lausanne, Switzerland. Even though Arafat's symptoms
were acute gastroenteritis with diarrhoea and vomiting, the
institute's spokesman said that despite the tests the symptoms
described in Arafat's medical reports were not consistent with 210Po
poisoning, and conclusions could not be drawn. In 2013 the team found
levels of polonium in Arafat's ribs and pelvis 18 to 36 times the
average, even though by this point in time the amount had diminished
by a factor of 2 million. 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."
Subsequently, French and Russian teams claimed that the elevated 210Po
levels were not the result of deliberate poisoning, and did not cause
Arafat's death.
It has also been suspected that Russian businessman Roman Tsepov was
killed with polonium. He had symptoms similar to Aleksander
Litvinenko.
Treatment
===========
It has been suggested that chelation agents, such as British
anti-Lewisite (dimercaprol), can be used to decontaminate humans. 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 five months.
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.
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.
As early as the 1920s, French biologist 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. 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 and that
similar patterns of distribution occur in human tissues. 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.
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.
The presence of polonium in tobacco smoke has been known since the
early 1960s. 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.
Food
======
Polonium is found in the food chain, especially in seafood.
In popular culture
====================
Polonium poisoning has been used as a plot point on the American
daytime television show General Hospital for many years.
See also
======================================================================
* Polonium halo
* Poisoning of Alexander Litvinenko
External links
======================================================================
* [
http://www.periodicvideos.com/videos/084.htm Polonium] at 'The
Periodic Table of Videos' (University of Nottingham)
License
=========
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License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Polonium
