Polonium-210#210Po

File:Decay chain(4n+2, Uranium series).svg, known as the uranium series or radium series, of which polonium-210 is a member]]

File:S-R-processes-atomic-mass-201-to-210.svg. The red path represents the sequence of neutron captures; blue and cyan arrows represent beta decay, and the green arrow represents the alpha decay of ²¹⁰Po. It is the short half-lives of ²¹⁰Bi and ²¹⁰Po that prevent the formation of heavier elements, instead resulting in a cycle of four neutron captures, two beta decays, and an alpha decay.]]

In 1898, Marie and Pierre Curie discovered a strongly radioactive substance in pitchblende and determined that it was a new element; it was one of the first radioactive elements discovered. Having identified it as such, they named the element polonium after Marie's home country, Poland. Willy Marckwald discovered a similar radioactive activity in 1902 and named it radio-tellurium, and at roughly the same time, Ernest Rutherford identified the same activity in his analysis of the uranium decay chain and named it radium F (originally radium E). By 1905, Rutherford concluded that all these observations were due to the same substance, ²¹⁰Po. Further discoveries and the concept of isotopes, first proposed in 1913 by Frederick Soddy, firmly placed ²¹⁰Po as the penultimate step in the uranium series.{{Thoennessen2016|pages=6–8}}

In 1943, ²¹⁰Po was studied as a possible neutron initiator in nuclear weapons, as part of the Dayton Project. In subsequent decades, concerns for the safety of workers handling ²¹⁰Po led to extensive studies on its health effects.{{cite magazine |last=Roessler |first=G. |title=Why ²¹⁰Po? |url=https://hps.org/documents/polonium_210_story.pdf |magazine=Health Physics News |publisher=Health Physics Society |date=2007 |volume=35 |issue=2 |access-date=2019-06-20 |archive-url=https://web.archive.org/web/20140403100938/http://hps.org/documents/polonium_210_story.pdf |archive-date=2014-04-03 |url-status=live }}

In the 1950s, scientists of the United States Atomic Energy Commission at Mound Laboratories, Ohio explored the possibility of using ²¹⁰Po in radioisotope thermoelectric generators (RTGs) as a heat source to power satellites. A 2.5-watt atomic battery using ²¹⁰Po was developed by 1958. However, the isotope plutonium-238 was chosen instead, as it has a longer half-life of 87.7 years.{{cite book |chapter-url=https://inl.gov/wp-content/uploads/2014/10/AtomicPowerInSpaceII-AHistory_2015_chapters1-2.pdf |chapter=The Early Years: Space Nuclear Power Systems Take Flight |title=Atomic power in space II: a history of space nuclear power and propulsion in the United States. |oclc=931595589 |author=Idaho National Laboratory |date=2015 |pages=2–5|author-link=Idaho National Laboratory }}

Polonium-210 was used to kill Russian dissident and ex-FSB officer Alexander V. Litvinenko in 2006,{{cite journal |last1=McFee |first1=R. B. |last2=Leikin |first2=J. B. |date=2009 |title=Death by polonium-210: lessons learned from the murder of former Soviet spy Alexander Litvinenko |url=https://www.researchgate.net/publication/24206298 |journal=Seminars in Diagnostic Pathology |volume=26 |issue=1 |pages=61–67 |doi=10.1053/j.semdp.2008.12.003 |pmid=19292030}}{{cite news |first=A. |last=Cowell |date=November 24, 2006 |title=Radiation Poisoning Killed Ex-Russian Spy |url=https://www.nytimes.com/2006/11/24/world/europe/25spycnd.html |work=The New York Times |access-date=June 19, 2019 |archive-url=https://web.archive.org/web/20190619142636/https://www.nytimes.com/2006/11/24/world/europe/25spycnd.html |archive-date=June 19, 2019 |url-status=live }} and was suspected as a possible cause of Yasser Arafat's death, following exhumation and analysis of his corpse in 2012–2013.{{cite web|title=Arafat's death: what is Polonium-210?|url=http://www.aljazeera.com/video/asia-pacific/2012/07/2012746748407858.html|work=Al Jazeera|date=July 10, 2012|access-date=June 19, 2019|archive-url=https://web.archive.org/web/20190619142649/https://www.aljazeera.com/video/asia-pacific/2012/07/2012746748407858.html|archive-date=June 19, 2019|url-status=live}} The radioisotope may also have been used to kill Yuri Shchekochikhin, Lecha Islamov and Roman Tsepov.{{cite book | last1=Sweeney | first1=J. | title=Killer in the Kremlin | page=120 | year=2022 | isbn=9781804991206 | publisher=Penguin }}

²¹⁰Po is an alpha emitter that has a half-life of 138.376 days; it decays directly to stable ²⁰⁶Pb. The majority of the time, ²¹⁰Po decays by emission of an alpha particle only, not by emission of an alpha particle and a gamma ray; about one in 100,000 decays results in the emission of a gamma ray.{{cite web |work=Korea Atomic Energy Research Institute |url=http://atom.kaeri.re.kr/cgi-bin/decay?Po-210%20A |title=210Po A Decay|archive-url=https://web.archive.org/web/20150224043744/http://atom.kaeri.re.kr/cgi-bin/decay?Po-210+A |archive-date=February 24, 2015 }}

:$\backslash mathrm\{$

^{210}_{\ 84}Po\ \xrightarrow [138.376 \ d]{}\ ^{206}_{\ 82}Pb\ + ^{\ 4}_{\ 2}He

}

This low gamma ray production rate makes it more difficult to find and identify this isotope. Rather than gamma ray spectroscopy, alpha spectroscopy is the best method of measuring this isotope.

Owing to its much shorter half-life, a milligram of ²¹⁰Po emits as many alpha particles per second as 5 grams of ²²⁶Ra.{{cite web |title=The Elements |author=C. R. Hammond |publisher=Fermi National Accelerator Laboratory |pages=4–22 |url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elements.pdf |access-date=2019-06-19 |archive-url=https://web.archive.org/web/20080626181434/http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elements.pdf |archive-date=2008-06-26 |url-status=live }} A few curies of ²¹⁰Po emit a blue glow caused by excitation of surrounding air.

²¹⁰Po occurs in minute amounts in nature, where it is the penultimate isotope in the uranium series decay chain. It is generated via beta decay from ²¹⁰Pb and ²¹⁰Bi.

The astrophysical s-process is terminated by the decay of ²¹⁰Po, as the neutron flux is insufficient to lead to further neutron captures in the short lifetime of ²¹⁰Po. Instead, ²¹⁰Po alpha decays to ²⁰⁶Pb, which then captures more neutrons to become ²¹⁰Po and repeats the cycle, thus consuming the remaining neutrons. This results in a buildup of lead and bismuth, and ensures that heavier elements such as thorium and uranium are only produced in the much faster r-process.{{cite journal |last1=Burbidge |first1=E. M. |last2=Burbidge |first2=G. R. |last3=Fowler |first3=W. A. |last4=Hoyle |first4=F. |date=1957 |title=Synthesis of the Elements in Stars |journal=Reviews of Modern Physics |volume=29 |issue=4 |pages=547–650 |bibcode=1957RvMP...29..547B |doi=10.1103/RevModPhys.29.547 |doi-access=free}}

Although ²¹⁰Po occurs in trace amounts in nature, it is not abundant enough (0.1 ppb) for extraction from uranium ore to be feasible. Instead, most ²¹⁰Po is produced synthetically, through neutron bombardment of ²⁰⁹Bi in a nuclear reactor. This process converts ²⁰⁹Bi to ²¹⁰Bi, which beta decays to ²¹⁰Po with a five-day half-life.https://doh.wa.gov/sites/default/files/legacy/Documents/Pubs//320-091_po210_fs.pdf Through this method, approximately {{Convert|8|g}} of ²¹⁰Po are produced in Russia and shipped to the United States every month for commercial applications. 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.{{cite journal |title =Neutronic Chain Reactions for Polonium-210 Production |first =Solomon |last = Lim |journal = SSRN |date = 2023 |doi = 10.2139/ssrn.4469519|url =https://hal.science/hal-04196973/file/Report%20210.pdf }}

The production of polonium-210 is a downside to reactors cooled with lead-bismuth eutectic rather than pure lead. However, given the eutectic properties of this alloy, some proposed Generation IV reactor designs still rely on lead-bismuth.

A single gram of ²¹⁰Po generates 140 watts of power.{{Cite web|url = http://www.ead.anl.gov/pub/doc/polonium.pdf|title = Polonium|publisher = Argonne National Laboratory|archive-url = https://web.archive.org/web/20120310145431/http://www.ead.anl.gov/pub/doc/polonium.pdf|archive-date = 2012-03-10}} Because it emits many alpha particles, which are stopped within a very short distance in dense media and release their energy, ²¹⁰Po has been used as a lightweight heat source to power thermoelectric cells in artificial satellites. A ²¹⁰Po heat source was also in each of the Lunokhod rovers deployed on the surface of the Moon, to keep their internal components warm during the lunar nights.A. Wilson, Solar System Log, (London: Jane's Publishing Company Ltd, 1987), p. 64.{{ISBN?}} Some anti-static brushes, used for neutralizing static electricity on materials like photographic film, contain a few microcuries of ²¹⁰Po as a source of charged particles.{{cite web |publisher=Company 7 |title=Staticmaster Alpha Ionizing Brush |url=http://www.company7.com/staticmaster/products/staticmaster.html |access-date=2019-06-19 |archive-url=https://web.archive.org/web/20180927235206/http://www.company7.com/staticmaster/products/staticmaster.html |archive-date=2018-09-27 |url-status=live }} ²¹⁰Po was also used in initiators for atomic bombs through the (α,n) reaction with beryllium.{{cite book |first1=L. |last1=Hoddeson |first2=P. W. |last2=Henriksen |first3=R. A. |last3=Meade|title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945|url=https://books.google.com/books?id=KoTve97yYB8C|year=2004|publisher=Cambridge University Press|isbn=978-0-521-54117-6}} Small neutron sources reliant on the (α,n) reaction also usually use polonium as a convenient source of alpha particles due to its comparatively low gamma emissions (allowing easy shielding) and high specific activity.

{{main|Polonium#Biology and toxicity}}

²¹⁰Po is extremely toxic; it and other polonium isotopes are some of the most radiotoxic substances to humans.{{cite journal |last1=Skwarzec |first1=B. |last2=Strumińska |first2=D. I. |last3=Boryło |first3=A. |title=Radionuclides of iron (⁵⁵Fe), nickel (⁶³Ni), polonium (²¹⁰Po), uranium (²³⁴U, ²³⁵U, ²³⁸U), and plutonium (²³⁸Pu, ^239+240Pu, ²⁴¹Pu) in Poland and Baltic Sea environment |journal=Nukleonika |year=2006 |volume=51 |pages=S45–S51 |url=http://www.nukleonika.pl/www/back/full/vol51_2006/v51s2p45f.pdf |access-date=2019-06-19 |archive-url=https://web.archive.org/web/20190619142638/http://www.nukleonika.pl/www/back/full/vol51_2006/v51s2p45f.pdf |archive-date=2019-06-19 |url-status=live }} With one microgram of ²¹⁰Po being more than enough to kill the average adult, it is 250,000 times more toxic than hydrogen cyanide by weight.{{cite journal |last1=Ahmed |first1=M. F. |last2=Alam |first2=L. |last3=Mohamed |first3=C. A. R. |last4=Mokhtar |first4=M. B. |last5=Ta |first5=G. C. |title=Health risk of polonium-210 ingestion via drinking water: An experience of Malaysia |journal=International Journal of Environmental Research and Public Health |date=2018 |volume=15 |issue=10 |pages=2056–1–2056–19 |doi=10.3390/ijerph15102056 |pmid=30241360 |pmc=6210456 |doi-access=free }} One gram of ²¹⁰Po would hypothetically be enough to kill 50 million people and sicken another 50 million. This is a consequence of its ionizing alpha radiation, as alpha particles are especially damaging to organic tissues inside the body. However, ²¹⁰Po does not pose a radiation hazard when contained outside the body.{{Cite web |date=2019-02-11 |title=Radiation Studies: CDC - Radiation: Polonium-210 {{!}} CDC RSB |url=https://www.cdc.gov/nceh/radiation/polonium-210.htm |access-date=2022-11-14 |website=www.cdc.gov |language=en-us}} The alpha particles it produces cannot penetrate the outer layer of dead skin cells.{{Cite web |title=Penetration Abilities of Different Types of Radiation |url=https://www.cdc.gov/training/products/RN/page4976.html |access-date=2022-11-14 |website=www.cdc.gov}}

The toxicity of ²¹⁰Po stems entirely from its radioactivity. It is not chemically toxic in itself, but its solubility in aqueous solution as well as that of its salts poses a hazard because its spread throughout the body is facilitated in solution. Intake of ²¹⁰Po occurs primarily through contaminated air, food, or water, as well as through open wounds. Once inside the body, ²¹⁰Po concentrates in soft tissues (especially in the reticuloendothelial system) and the bloodstream. Its biological half-life is approximately 50 days.{{cite report |url=https://www.cdc.gov/nceh/radiation/fallon/Polonium_factsheet.pdf |title=Frequently asked questions about polonium-210. |publisher=Centers for Disease Control and Prevention |access-date=19 June 2019 |archive-url=https://web.archive.org/web/20170607100124/https://www.cdc.gov/nceh/radiation/fallon/polonium_factsheet.pdf |archive-date=7 June 2017 |url-status=live }}

In the environment, ²¹⁰Po can accumulate in seafood.{{cite journal |last1=Richter |first1=F. |last2=Wagmann |first2=M. |last3=Zehringer |first3=M. |title=Polonium – on the Trace of a Powerful Alpha Nuclide in the Environment |journal=CHIMIA International Journal for Chemistry |date=2012 |volume=66 |issue=3 |pages=131 |doi=10.2533/chimia.2012.131 |url=https://www.researchgate.net/publication/224869922 |access-date=2019-06-19 |archive-url=https://web.archive.org/web/20190217142359/https://www.researchgate.net/publication/224869922_Polonium_-_on_the_Trace_of_a_Powerful_Alpha_Nuclide_in_the_Environment |archive-date=2019-02-17 |url-status=live |doi-access=free }} It has been detected in various organisms in the Baltic Sea, where it can propagate in, and thus contaminate, the food chain. ²¹⁰Po is also known to contaminate vegetation, primarily originating from the decay of atmospheric radon-222 and absorption from soil.

In particular, ²¹⁰Po attaches to, and concentrates in, tobacco leaves. Elevated concentrations of ²¹⁰Po in tobacco were documented as early as 1964, and cigarette smokers were thus found to be exposed to considerably greater doses of radiation from ²¹⁰Po and its parent ²¹⁰Pb.{{cite conference |date=2009 |last1=Persson |first1=B. R. R. |last2=Holm |first2=E. |title=Polonium-210 and Lead-210 in the Terrestrial environment: A historical review |conference=International Topical Conference on Po and Radioactive Pb Isotopes |location=Seville, Spain |url=https://www.researchgate.net/publication/256456252}} Heavy smokers may be exposed to the same amount of radiation (estimates vary from 100 µSv to 160 mSv{{Cite web|archive-url=https://web.archive.org/web/20130613131654/http://www.ors.od.nih.gov/sr/drs/training/GRS/Pages/sectionf.aspx|title=F. Typical Sources of Radiation Exposure |archive-date=2013-06-13 |access-date=2019-06-20 |publisher=National Institute of Health |url-status=dead |url=http://www.ors.od.nih.gov/sr/drs/training/GRS/Pages/sectionf.aspx}} per year) as individuals in Poland were from Chernobyl fallout traveling from Ukraine. As a result, ²¹⁰Po is most dangerous when inhaled from cigarette smoke.{{cite journal|jstor=1712451|title=Polonium-210: A Volatile Radioelement in Cigarettes|journal=Science|volume=143|issue=3603|pages=247–249|last1=Radford|first1=E. P.|last2=Hunt|first2=V. R.|year=1964|doi=10.1126/science.143.3603.247|pmid=14078362|bibcode=1964Sci...143..247R|s2cid=23455633}}

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