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{{About|the chemical element}}
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'''Plutonium''' is a [[chemical element]]; it has [[Chemical symbol|symbol]] '''Pu''' and [[atomic number]] 94. It is a silvery-gray [[actinide]] [[metal]] that [[tarnish]]es when exposed to air, and forms a dull coating [[plutonium(IV) oxide|when oxidized]]. The element normally exhibits six [[allotrope]]s and four [[oxidation state]]s. It reacts with [[carbon]], [[halogen]]s, [[nitrogen]], [[silicon]], and [[hydrogen]]. When exposed to moist air, it forms [[oxide]]s and [[hydride]]s that can expand the sample up to 70% in volume, which in turn flake off as a powder that is [[pyrophoricity|pyrophoric]]. It is [[radioactive]] and can accumulate in [[bone]]s, which makes the handling of plutonium dangerous.

Plutonium was first synthesized and isolated in late 1940 and early 1941, by [[deuteron]] bombardment of [[uranium-238]] in the {{convert|1.5|m|in|-1|adj=on}} [[cyclotron]] at the [[University of California, Berkeley]]. First, [[neptunium-238]] ([[half-life]] 2.1 days) was synthesized, which then [[beta-decay]]ed to form the new element with atomic number 94 and atomic weight 238 (half-life 88 years). Since [[uranium]] had been named after the planet [[Uranus]] and [[neptunium]] after the planet [[Neptune]], element 94 was named after [[Pluto]], which at the time was also considered a planet. Wartime secrecy prevented the University of California team from publishing its discovery until 1948.

Plutonium is the element with the highest atomic number known to occur in nature. Trace quantities arise in natural uranium deposits when uranium-238 captures neutrons emitted by decay of other uranium-238 atoms. The heavy isotope [[plutonium-244]] has a half-life long enough that extreme [[trace element|trace quantities]] should have survived [[primordial nuclide|primordially]] (from the Earth's formation) to the present, but so far experiments have not yet been sensitive enough to detect it.

Both [[plutonium-239]] and [[plutonium-241]] are [[fissile]], meaning they can sustain a [[nuclear chain reaction]], leading to applications in [[nuclear weapon]]s and [[nuclear reactor]]s. [[Plutonium-240]] has a high rate of [[spontaneous fission]], raising the [[neutron flux]] of any sample containing it. The presence of plutonium-240 limits a plutonium sample's usability for weapons or its quality as reactor fuel, and the percentage of plutonium-240 determines its [[reactor-grade plutonium|grade]] ([[weapons-grade]], fuel-grade, or reactor-grade). [[Plutonium-238]] has a half-life of 87.7 years and emits [[alpha particle]]s. It is a heat source in [[radioisotope thermoelectric generator]]s, which are used to power some [[spacecraft]]. Plutonium isotopes are expensive and inconvenient to separate, so particular isotopes are usually manufactured in specialized reactors.

Producing plutonium in useful quantities for the first time was a major part of the [[Manhattan Project]] during [[World War II]] that developed the first atomic bombs. The [[Fat Man]] bombs used in the [[Trinity (nuclear test)|Trinity]] [[nuclear test]] in July 1945, and in the [[bombing of Nagasaki]] in August 1945, had plutonium [[pit (nuclear weapon)|cores]]. [[Human radiation experiments]] studying plutonium were conducted without [[informed consent]], and several [[criticality accident]]s, some lethal, occurred after the war. Disposal of [[nuclear waste|plutonium waste]] from [[nuclear power plant]]s and [[nuclear disarmament|dismantled nuclear weapons]] built during the [[Cold War]] is a [[nuclear proliferation|nuclear-proliferation]] and environmental concern. Other sources of [[plutonium in the environment]] are [[nuclear fallout|fallout]] from many above-ground nuclear tests, which are now [[Partial Test Ban Treaty|banned]].

==Characteristics==
===Physical properties===
Plutonium, like most metals, has a bright silvery appearance at first, much like [[nickel]], but it [[plutonium(IV) oxide|oxidizes]] very quickly to a dull gray, though yellow and olive green are also reported.<ref name="WISER">{{Cite web |title=Plutonium, Radioactive |url=http://webwiser.nlm.nih.gov/getSubstanceData.do;jsessionid=89B673C34252C77B4C276F2B2D0E4260?substanceID=419&displaySubstanceName=Plutonium,%20Radioactive&UNNAID=&STCCID=&selectedDataMenuItemID=44 |url-status=dead |archive-url=https://web.archive.org/web/20110813103852/http://webwiser.nlm.nih.gov/getSubstanceData.do;jsessionid=89B673C34252C77B4C276F2B2D0E4260?substanceID=419&displaySubstanceName=Plutonium,%20Radioactive&UNNAID=&STCCID=&selectedDataMenuItemID=44 |archive-date=August 13, 2011 |access-date=November 23, 2008 |website=Wireless Information System for Emergency Responders (WISER) |publisher=U.S. National Library of Medicine, National Institutes of Health |location=Bethesda (MD)}} (public domain text)</ref><ref>{{Cite journal |date=2008 |title=Nitric acid processing |url=http://www.lanl.gov/discover/publications/actinide-research-quarterly/ |url-status=live |journal=Actinide Research Quarterly |location=Los Alamos (NM) |publisher=Los Alamos National Laboratory |issue=3rd quarter |archive-url=https://web.archive.org/web/20160918212329/http://www.lanl.gov/discover/publications/actinide-research-quarterly/ |archive-date=September 18, 2016 |access-date=February 9, 2010 |quote=While plutonium dioxide is normally olive green, samples can be various colors. It is generally believed that the color is a function of chemical purity, stoichiometry, particle size, and method of preparation, although the color resulting from a given preparation method is not always reproducible.}}</ref> At [[room temperature]] plutonium is in its [[allotropes of plutonium|α (''alpha'') form]].<ref>visualisation of the crystal structure at [https://log-web.de/chemie/Start.htm?name=Pu_alpha&lang=en log-web.de]</ref>  This [[allotrope]] is about as hard and brittle as [[cast iron#Grey cast iron|gray cast iron]]. When plutonium is [[alloy]]ed with other metals, the high-temperature δ [[allotrope]] is stabilized at room temperature,<ref>Babak Sadigh, Per Söderlind, and Wilhelm G. Wolfer (2003): Geometry and electronic structure of δ-Pu: A theoretical study. Physical Review B 68, 241101(R) </ref><ref>K. T. Moore, P. Söderlind, A. J. Schwartz, and D. E. Laughlin (2006): Symmetry and Stability of δ Plutonium: The Influence of Electronic Structure. Physical Review Letters 96, 206402.</ref> making it soft and ductile. Unlike most metals, it is not a good conductor of [[thermal conductivity|heat]] or [[electrical conductivity|electricity]]. It has a low [[melting point]] ({{convert|640|°C|disp=comma}}) and an unusually high [[boiling point]] ({{convert|3228|°C|disp=comma}}).<ref name="WISER" /> This gives a large range of temperatures (over 2,500 kelvin wide) at which plutonium is liquid, but this range is neither the greatest among all actinides nor among all metals,<ref>{{Cite web |title=Liquid Range |url=https://www.webelements.com/periodicity/liquid_range/ |url-status=live |archive-url=https://web.archive.org/web/20220227135806/https://www.webelements.com/periodicity/liquid_range/ |archive-date=February 27, 2022 |access-date=28 February 2022 |website=webelements.com}}</ref> with neptunium theorized to have the greatest range in both instances. The low melting point as well as the reactivity of the native metal compared to the oxide leads to [[plutonium oxide]]s being a preferred form for applications such as nuclear fission reactor fuel ([[MOX-fuel]]).

[[Alpha decay]], the release of a high-energy [[helium]] nucleus, is the most common form of [[radioactive decay]] for plutonium.<ref name="NNDC" /> A 5&nbsp;kg mass of {{sup|239}}Pu contains about {{val|12.5|e=24}} atoms. With a half-life of 24,100 years, about {{val|11.5|e=12}} of its atoms decay each second by emitting a 5.157&nbsp;[[MeV]] alpha particle. This amounts to 9.68 watts of power. Heat produced by the deceleration of these alpha particles makes it warm to the touch.<ref name="Heiserman1992">{{harvnb|Heiserman|1992|p=338}}</ref><ref>{{harvnb|Rhodes|1986|pp=659–660}} [[Leona Marshall]]: "When you hold a lump of it in your hand, it feels warm, like a live rabbit"</ref> {{chem|238|Pu}} due to its much shorter [[half life]] heats up to much higher temperatures and glows red hot with [[blackbody radiation]] if left without external heating or cooling. This heat has been used in [[radioisotope thermoelectric generator]]s (see below).

The [[Electrical resistivity and conductivity|resistivity]] of plutonium at room temperature is very high for a metal, and it gets even higher with lower temperatures, which is unusual for metals.<ref name="Miner1968p544" /> This trend continues down to 100&nbsp;[[Kelvin|K]], below which resistivity rapidly decreases for fresh samples.<ref name="Miner1968p544" /> Resistivity then begins to increase with time at around 20&nbsp;K due to radiation damage, with the rate dictated by the isotopic composition of the sample.<ref name="Miner1968p544" />

Because of self-irradiation, a sample of plutonium [[Fatigue (material)|fatigue]]s throughout its crystal structure, meaning the ordered arrangement of its atoms becomes disrupted by radiation with time.<ref name="HeckerPlutonium" /> Self-irradiation can also lead to [[annealing (metallurgy)|annealing]] which counteracts some of the fatigue effects as temperature increases above 100&nbsp;K.<ref>{{Cite journal |last1=Hecker |first1=Siegfried S. |last2=Martz, Joseph C. |date=2000 |title=Aging of Plutonium and Its Alloys |url=http://library.lanl.gov/cgi-bin/getfile?00818029.pdf |url-status=live |journal=[[Los Alamos Science]] |location=Los Alamos, New Mexico |publisher=Los Alamos National Laboratory |issue=26 |page=242 |archive-url=https://web.archive.org/web/20210428114802/https://library.lanl.gov/cgi-bin/getfile?00818029.pdf |archive-date=April 28, 2021 |access-date=February 15, 2009}}</ref>

Unlike most materials, plutonium increases in density when it melts, by 2.5%, but the liquid metal exhibits a linear decrease in density with temperature.<ref name="Miner1968p544">{{harvnb|Miner|1968|p = 544}}</ref> Near the melting point, the liquid plutonium has very high [[viscosity]] and [[surface tension]] compared to other metals.<ref name="HeckerPlutonium" />

===Allotropes===
{{Main|Allotropes of plutonium}}
[[File:Plutonium density-eng.svg|thumb|upright=1.2|Plutonium has six allotropes at ambient pressure: '''alpha'''&nbsp;(α), '''beta'''&nbsp;(β), '''gamma'''&nbsp;(γ), '''delta'''&nbsp;(δ), '''delta&nbsp;prime'''&nbsp;(δ'), and '''epsilon'''&nbsp;(ε).<ref name="Baker1983" />|alt=A graph showing change in density with increasing temperature upon sequential phase transitions between alpha, beta, gamma, delta, delta' and epsilon phases]]
Plutonium normally has six [[allotrope]]s and forms a seventh (zeta, ζ) at high temperature within a limited pressure range.<ref name="Baker1983">{{Cite journal |last1=Baker |first1=Richard D. |last2=Hecker |first2=Siegfried S. |last3=Harbur |first3=Delbert R. |date=1983 |title=Plutonium: A Wartime Nightmare but a Metallurgist's Dream |url=http://library.lanl.gov/cgi-bin/getfile?07-16.pdf |url-status=live |journal=Los Alamos Science |publisher=Los Alamos National Laboratory |pages=148, 150–151 |archive-url=https://web.archive.org/web/20111017034523/http://library.lanl.gov/cgi-bin/getfile?07-16.pdf |archive-date=October 17, 2011 |access-date=February 15, 2009}}</ref><!-- Note: page 148 --> These allotropes, which are different structural modifications or forms of an element, have very similar [[internal energy|internal energies]] but significantly varying [[density|densities]] and [[crystal structure]]s. This makes plutonium very sensitive to changes in temperature, pressure, or chemistry, and allows for dramatic volume changes following [[phase transition]]s from one allotropic form to another.<ref name="HeckerPlutonium">{{Cite journal |last=Hecker |first=Siegfried S. |date=2000 |title=Plutonium and its alloys: from atoms to microstructure |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00818035.pdf |url-status=live |journal=Los Alamos Science |volume=26 |pages=290–335 |archive-url=https://web.archive.org/web/20090224204042/http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818035.pdf |archive-date=February 24, 2009 |access-date=February 15, 2009}}</ref> The densities of the different allotropes vary from 16.00&nbsp;g/cm{{sup|3}} to 19.86&nbsp;g/cm{{sup|3}}.<ref name="CRC2006p4-27" />

The presence of these many allotropes makes machining plutonium very difficult, as it changes state very readily. For example, the α form exists at room temperature in unalloyed plutonium. It has machining characteristics similar to [[cast iron]] but changes to the plastic and malleable β (''beta'') form at slightly higher temperatures.<ref name="Miner1968p542" /> The reasons for the complicated phase diagram are not entirely understood. The α form has a low-symmetry [[monoclinic crystal system|monoclinic]] structure, hence its brittleness, strength, compressibility, and poor thermal conductivity.<ref name="Baker1983" />

Plutonium in the δ (''delta'') form normally exists in the 310&nbsp;°C to 452&nbsp;°C range but is stable at room temperature when alloyed with a small percentage of [[gallium]], [[aluminium]], or [[cerium]], enhancing workability and allowing it to be [[welding|welded]].<ref name="Miner1968p542" /> The δ form has more typical metallic character, and is roughly as strong and malleable as aluminium.<ref name="Baker1983" /> In fission weapons, the explosive [[shock wave]]s used to compress a plutonium core will also cause a transition from the usual δ phase plutonium to the denser α form, significantly helping to achieve [[supercriticality]].{{citation needed|date=February 2023}} The ε phase, the highest temperature solid allotrope, exhibits anomalously high atomic [[self-diffusion]] compared to other elements.<ref name="HeckerPlutonium" />

===Nuclear fission===
Plutonium is a radioactive [[actinide]] metal whose [[isotope]], [[plutonium-239]], is one of the three primary [[fissile]] isotopes ([[uranium-233]] and [[uranium-235]] are the other two); [[plutonium-241]] is also highly fissile. To be considered fissile, an isotope's [[atomic nucleus]] must be able to break apart or [[nuclear fission|fission]] when struck by a [[neutron temperature|slow moving neutron]] and to release enough additional neutrons to sustain the [[nuclear chain reaction]] by splitting further nuclei.<ref>{{Cite web |date=November 20, 2014 |title=Glossary – Fissile material |url=https://www.nrc.gov/reading-rm/basic-ref/glossary/fissile-material.html |url-status=live |archive-url=https://web.archive.org/web/20150204223452/http://www.nrc.gov/reading-rm/basic-ref/glossary/fissile-material.html |archive-date=February 4, 2015 |access-date=February 5, 2015 |publisher=[[United States Nuclear Regulatory Commission]]}}</ref>

Pure plutonium-239 may have a [[four factor formula|multiplication factor]] (k<sub>eff</sub>) larger than one, which means that if the metal is present in sufficient quantity and with an appropriate geometry (e.g., a sphere of sufficient size), it can form a [[critical mass]].<ref>{{harvnb|Asimov|1988|p=905}}</ref> During fission, a fraction of the [[nuclear binding energy]], which holds a nucleus together, is released as a large amount of [[Electromagnetism|electromagnetic]] and [[kinetic energy]] (much of the latter being quickly converted to thermal energy). Fission of a kilogram of plutonium-239 can produce an explosion equivalent to {{convert|21,000|tonTNT|lk=on}}. It is this energy that makes plutonium-239 useful in [[nuclear weapon]]s and [[nuclear reactor|reactors]].<ref name="Heiserman1992" />

The presence of the isotope [[plutonium-240]] in a sample limits its nuclear bomb potential, as {{sup|240}}Pu has a relatively high [[spontaneous fission]] rate (~440 fissions per second per gram; over 1,000 neutrons per second per gram),<ref>{{Cite web |last1=Glasstone |first1=Samuel |last2=Redman |first2=Leslie M. |date=June 1972 |title=An Introduction to Nuclear Weapons |url=http://www.doeal.gov/opa/docs/RR00171.pdf |archive-url=https://web.archive.org/web/20090827082245/http://www.doeal.gov/opa/docs/RR00171.pdf |archive-date=August 27, 2009 |publisher=Atomic Energy Commission Division of Military Applications |page=12 |id=WASH-1038}}</ref> raising the background neutron levels and thus increasing the risk of [[fizzle (nuclear test)|predetonation]].<ref>{{harvnb|Gosling|1999|p=40}}</ref> Plutonium is identified as either [[weapons-grade]], fuel-grade, or reactor-grade based on the percentage of {{sup|240}}Pu that it contains. Weapons-grade plutonium contains less than 7% {{sup|240}}Pu. [[reactor-grade plutonium|Fuel-grade plutonium]] contains 7%–19%, and power reactor-grade contains 19% or more {{sup|240}}Pu. [[plutonium-239#Supergrade plutonium|Supergrade plutonium]], with less than 4% of {{sup|240}}Pu, is used in [[U.S. Navy]] weapons stored near ship and submarine crews, due to its lower radioactivity.<ref>{{Cite web |date=1996 |title=Plutonium: The First 50 Years |url=http://www.doeal.gov/SWEIS/DOEDocuments/004%20DOE-DP-0137%20Plutonium%2050%20Years.pdf |archive-url=https://web.archive.org/web/20130218162928/http://www.doeal.gov/SWEIS/DOEDocuments/004%20DOE-DP-0137%20Plutonium%2050%20Years.pdf |archive-date=February 18, 2013 |publisher=U.S. Department of Energy |id=DOE/DP-1037}}</ref> [[Plutonium-238]] is not [[fissile#Fissile vs fissionable|fissile but can undergo nuclear fission]] easily with [[fast neutrons]] as well as alpha decay.<ref name="Heiserman1992" /> All plutonium isotopes can be "bred" into fissile material with one or more [[neutron absorption]]s, whether followed by [[beta decay]] or not. This makes non-fissile isotopes of plutonium a [[fertile material]].

===Isotopes and nucleosynthesis===
[[File:PuIsotopes.svg|thumb|upright=1.5|Uranium-plutonium and thorium-uranium chains|alt=A diagram illustrating the interconversions between various isotopes of uranium, thorium, protactinium and plutonium]]
{{Main|Isotopes of plutonium}}
Twenty-two [[radioisotope]]s of plutonium have been characterized, from <sup>226</sup>Pu to <sup>247</sup>Pu. The longest-lived are {{sup|244}}Pu, with a half-life of 80.8&nbsp;million years; {{sup|242}}Pu, with a half-life of 373,300&nbsp;years; and {{sup|239}}Pu, with a half-life of 24,110&nbsp;years. All other isotopes have half-lives of less than 7,000&nbsp;years. This element also has eight [[meta state|metastable states]], though all have half-lives less than a second.<ref name="NNDC">{{Cite web |last=Sonzogni |first=Alejandro A. |date=2008 |title=Chart of Nuclides |url=http://www.nndc.bnl.gov/chart/ |url-status=dead |archive-url=https://web.archive.org/web/20110721051025/http://www.nndc.bnl.gov/chart/ |archive-date=July 21, 2011 |access-date=September 13, 2008 |publisher=National Nuclear Data Center, [[Brookhaven National Laboratory]] |location=Upton}}</ref> {{sup|244}}Pu has been found in interstellar space<ref name="WallnerFaestermann2015">{{Cite journal |last1=Wallner |first1=A. |last2=Faestermann |first2=T. |last3=Feige |first3=J. |last4=Feldstein |first4=C. |last5=Knie |first5=K. |last6=Korschinek |first6=G. |last7=Kutschera |first7=W. |last8=Ofan |first8=A. |last9=Paul |first9=M. |last10=Quinto |first10=F. |last11=Rugel |first11=G. |last12=Steier |first12=P. |year=2015 |title=Abundance of live 244Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis |journal=Nature Communications |volume=6 |pages=5956 |arxiv=1509.08054 |bibcode=2015NatCo...6.5956W |doi=10.1038/ncomms6956 |issn=2041-1723 |pmc=4309418 |pmid=25601158}}</ref> and it has the longest half-life of any non-primordial radioisotope. The main decay modes of isotopes with mass numbers lower than the most stable isotope, {{sup|244}}Pu, are spontaneous fission and [[alpha emission]], mostly forming uranium (92 [[proton]]s) and [[neptunium]] (93 protons) isotopes as [[decay product]]s (neglecting the wide range of daughter nuclei created by fission processes). The main decay mode for isotopes heavier than {{sup|244}}Pu, along with {{sup|241}}Pu and {{sup|243}}Pu, is [[beta emission]], forming [[americium]] isotopes (95 protons). Plutonium-241 is the [[parent isotope]] of the [[neptunium series]], decaying to americium-241 via beta emission.<ref name="NNDC" /><ref name="p340">{{harvnb|Heiserman|1992|p=340}}</ref>

Plutonium-238 and 239 are the most widely synthesized isotopes.<ref name="Heiserman1992" /> {{sup|239}}Pu is synthesized via the following reaction using uranium (U) and neutrons (n) via beta decay (β{{sup|−}}) with neptunium (Np) as an intermediate:<ref>{{Cite journal |last1=Kennedy |first1=J. W. |last2=Seaborg, G. T. |last3=Segrè, E. |last4=Wahl, A. C. |date=1946 |title=Properties of Element 94 |journal=Physical Review |volume=70 |issue=7–8 |pages=555–556 |bibcode=1946PhRv...70..555K |doi=10.1103/PhysRev.70.555 |doi-access=free}}</ref>

:<chem>
{^{238}_{92}U} + {^{1}_{0}n} -> {^{239}_{92}U} ->[\beta^-] [23.5 \ \ce{min}] {^{239}_{93}Np} ->[\beta^-] [2.3565 \ \ce d] {^{239}_{94}Pu}
</chem>

Neutrons from the fission of uranium-235 are [[neutron capture|captured]] by uranium-238 nuclei to form uranium-239; a [[beta decay]] converts a neutron into a proton to form neptunium-239 (half-life 2.36&nbsp;days) and another beta decay forms plutonium-239.<ref name="Greenwood1997p1259">{{harvnb|Greenwood|1997|p = 1259}}</ref> [[Egon Bretscher]] working on the British [[Tube Alloys]] project predicted this reaction theoretically in 1940.{{sfn|Clark|1961|pp=124–125}}

Plutonium-238 is synthesized by bombarding uranium-238 with [[deuteron]]s (D or {{sup|2}}H, the nuclei of heavy [[hydrogen]]) in the following reaction:<ref>{{Cite journal |last1=Seaborg |first1=Glenn T. |last2=McMillan, E. |last3=Kennedy, J. W. |last4=Wahl, A. C. |date=1946 |title=Radioactive Element 94 from Deuterons on Uranium |journal=Physical Review |volume=69 |issue=7–8 |pages=366 |bibcode=1946PhRv...69..366S |doi=10.1103/PhysRev.69.366}}</ref>

:<math chem>\begin{align}
\ce{ {^{238}_{92}U} + {^{2}_{1}H} ->} &\ce{ {^{238}_{93}Np} + 2^{1}_{0}n} \\
&\ce{^{238}_{93}Np ->[\beta^-] [2.117 \ \ce d] {^{238}_{94}Pu} }
\end{align}</math>

where a deuteron hitting uranium-238 produces two neutrons and neptunium-238, which decays by emitting negative beta particles to form plutonium-238.{{sfn|Bernstein|2007|pp=76–77}} Plutonium-238 can also be produced by [[neutron irradiation]] of [[neptunium-237]].<ref>{{Cite web |last=Miotla |first=Dennis |date=21 April 2008 |title=Assessment of Plutonium-238 Production of Alternatives: Briefing for Nuclear Energy Advisory Committee |url=https://www.energy.gov/sites/prod/files/NEGTN0NEAC_PU-238_042108.pdf |url-status=live |archive-url=https://web.archive.org/web/20220316130014/https://www.energy.gov/sites/prod/files/NEGTN0NEAC_PU-238_042108.pdf |archive-date=March 16, 2022 |access-date=28 February 2022 |publisher=Energy.gov}}</ref>

===Decay heat and fission properties===
Plutonium isotopes undergo radioactive decay, which produces [[decay heat]]. Different isotopes produce different amounts of heat per mass. The decay heat is usually listed as watt/kilogram, or milliwatt/gram. In larger pieces of plutonium (e.g. a weapon pit) and inadequate heat removal the resulting self-heating may be significant.

{| class="wikitable"
|+ Decay heat of plutonium isotopes<ref>{{Cite web |date=May 2001 |title=Can Reactor Grade Plutonium Produce Nuclear Fission Weapons? |url=http://www.cnfc.or.jp/e/proposal/reports/index.html |url-status=live |archive-url=https://web.archive.org/web/20210224141047/http://www.cnfc.or.jp/e/proposal/reports/index.html |archive-date=February 24, 2021 |access-date=January 30, 2010 |publisher=Council for Nuclear Fuel Cycle Institute for Energy Economics, Japan}}</ref>
! Isotope !! [[Decay mode]] !! [[Half-life]] (years) !! [[Decay heat]] (W/kg) !! [[Spontaneous fission]] (SF) neutrons (1/(g·s)) !! Comment
|-
! [[plutonium-238|{{sup|238}}Pu]]
| alpha (α) to [[uranium-234|{{sup|234}}U]]
| 87.74
| 560
| 2600
| Very high decay heat. Even small amounts can cause significant self-heating. Used on its own in [[radioisotope thermoelectric generator]]s.
|-
! [[plutonium-239|{{sup|239}}Pu]]
| α to [[uranium-235|{{sup|235}}U]]
| 24100
| 1.9
| 0.022
| The main fissile isotope in use.
|-
! [[plutonium-240|{{sup|240}}Pu]]
| α to [[uranium-236|{{sup|236}}U]], SF
| 6560
| 6.8
| 910
| The main impurity in samples of {{sup|239}}Pu. The plutonium grade is usually listed as percentage of {{sup|240}}Pu. High rate of SF hinders use in nuclear weapons.
|-
! [[plutonium-241|{{sup|241}}Pu]]
| beta-minus, to [[Americium-241|{{sup|241}}Am]]
| 14.4
| 4.2
| 0.049
| Decays to americium-241; its buildup presents a radiation hazard in older samples.
|-
! [[plutonium-242|{{sup|242}}Pu]]
| α to [[uranium-238|{{sup|238}}U]]
| 376000
| 0.1
| 1700
| {{sup|242}}Pu α-decays to {{sup|238}}U; also decays by SF. 
|}

===Compounds and chemistry===
{{Main|Plutonium compounds}}
[[File:Plutonium in solution.jpg|thumb|Various oxidation states of plutonium in solution|alt=Five fluids in glass test tubes: violet, Pu(III); dark brown, Pu(IV)HClO4; light purple, Pu(V); light brown, Pu(VI); dark green, Pu(VII)]]
At room temperature, pure plutonium is silvery in color but gains a tarnish when oxidized.<ref>{{harvnb|Heiserman|1992|p=339}}</ref> The element displays four common ionic [[oxidation state]]s in [[aqueous solution]] and one rare one:<ref name="CRC2006p4-27" />
* Pu(III), as Pu<sup>3+</sup> (blue lavender)
* Pu(IV), as Pu<sup>4+</sup> (yellow brown)
* Pu(V), as {{chem|PuO|2|+}} (light pink){{efn|group = note|The {{chem|PuO|2|+}} ion is unstable in solution and will disproportionate into Pu<sup>4+</sup> and {{chem|PuO|2|2+}}; the Pu<sup>4+</sup> will then oxidize the remaining {{chem|PuO|2|+}} to {{chem|PuO|2|2+}}, being reduced in turn to Pu<sup>3+</sup>. Thus, aqueous solutions of {{chem|PuO|2|+}} tend over time towards a mixture of Pu<sup>3+</sup> and {{chem|PuO|2|2+}}. [[Uranium#Aqueous chemistry|{{chem|UO|2|+}}]] is unstable for the same reason.<ref>{{Cite web |last=Crooks |first=William J. |date=2002 |title=Nuclear Criticality Safety Engineering Training Module 10 – Criticality Safety in Material Processing Operations, Part 1 |url=http://ncsp.llnl.gov/ncset/Module10.pdf |url-status=dead |archive-url=https://web.archive.org/web/20060320153404/http://ncsp.llnl.gov/ncset/Module10.pdf |archive-date=March 20, 2006 |access-date=February 15, 2006}}</ref>}}
* Pu(VI), as {{chem|PuO|2|2+}} (pink orange)
* Pu(VII), as {{chem|PuO|5|3-}} (green)—the heptavalent ion is rare.

The color shown by plutonium solutions depends on both the oxidation state and the nature of the acid [[anion]].<ref>{{Cite book |last=Matlack |first=George |title=A Plutonium Primer: An Introduction to Plutonium Chemistry and its Radioactivity |date=2002 |publisher=Los Alamos National Laboratory |id=LA-UR-02-6594}}</ref> It is the acid anion that influences the degree of [[complex (chemistry)|complexing]]—how atoms connect to a central atom—of the plutonium species. Additionally, the formal +2 oxidation state of plutonium is known in the complex [K(2.2.2-cryptand)] [Pu<sup>II</sup>Cp″<sub>3</sub>], Cp″ = C<sub>5</sub>H<sub>3</sub>(SiMe<sub>3</sub>)<sub>2</sub>.<ref>{{Cite journal |last1=Windorff |first1=Cory J. |last2=Chen |first2=Guo P |last3=Cross |first3=Justin N |last4=Evans |first4=William J. |last5=Furche |first5=Filipp |last6=Gaunt |first6=Andrew J. |last7=Janicke |first7=Michael T. |last8=Kozimor |first8=Stosh A. |last9=Scott |first9=Brian L. |year=2017 |title=Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of <nowiki>{</nowiki>Pu<sup>II</sup><nowiki>[</nowiki>C<sub>5</sub>H<sub>3</sub>(SiMe<sub>3</sub>)<sub>2</sub><nowiki>]</nowiki><sub>3</sub><nowiki>}</nowiki><sup>−</sup> |journal=J. Am. Chem. Soc. |volume=139 |issue=11 |pages=3970–3973 |doi=10.1021/jacs.7b00706 |pmid=28235179}}</ref>

A +8 oxidation state is possible as well in the volatile tetroxide {{chem|Pu|O|4}}.<ref name="zaitsevskii">{{Cite journal |last1=Zaitsevskii |first1=Andréi |last2=Mosyagin |first2=Nikolai S. |last3=Titov |first3=Anatoly V. |last4=Kiselev |first4=Yuri M. |date=21 July 2013 |title=Relativistic density functional theory modeling of plutonium and americium higher oxide molecules |journal=The Journal of Chemical Physics |volume=139 |issue=3 |pages=034307 |bibcode=2013JChPh.139c4307Z |doi=10.1063/1.4813284 |pmid=23883027}}</ref> Though it readily decomposes via a reduction mechanism similar to {{chem|Fe|O|4}}, {{chem|Pu|O|4}} can be stabilized in alkaline solutions and [[chloroform]].<ref>{{Cite journal |last1=Kiselev |first1=Yu. M. |last2=Nikonov |first2=M. V. |last3=Dolzhenko |first3=V. D. |last4=Ermilov |first4=A. Yu. |last5=Tananaev |first5=I. G. |last6=Myasoedov |first6=B. F. |date=17 January 2014 |title=On existence and properties of plutonium(VIII) derivatives |journal=Radiochimica Acta |volume=102 |issue=3 |pages=227–237 |doi=10.1515/ract-2014-2146 |s2cid=100915090}}</ref><ref name="zaitsevskii" />

Metallic plutonium is produced by reacting [[plutonium tetrafluoride]] with [[barium]], [[calcium]] or [[lithium]] at 1200&nbsp;°C.<ref>{{harvnb|Eagleson|1994|p=840}}</ref> Metallic plutonium is attacked by [[acid]]s, [[oxygen]], and steam but not by [[alkalis]] and dissolves easily in concentrated [[hydrochloric acid|hydrochloric]], [[hydroiodic acid|hydroiodic]] and [[perchloric acid]]s.<ref name="Miner1968p545">{{harvnb|Miner|1968|p = 545}}</ref> Molten metal must be kept in a [[vacuum]] or an [[inert atmosphere]] to avoid reaction with air.<ref name="Miner1968p542">{{harvnb|Miner|1968|p = 542}}</ref> At 135&nbsp;°C the metal will ignite in air and will explode if placed in [[carbon tetrachloride]].<ref name="Emsley2001" />

[[File:Plutonium pyrophoricity.jpg|thumb|Plutonium [[pyrophoricity]] can cause it to look like a glowing ember under certain conditions.|alt=Black block of Pu with red spots on top and yellow powder around it]]
[[File:96602765.lowres.jpeg|thumb|upright|alt=Glass vial of brownish-white snow-like precipitation of plutonium hydroxide|Twenty micrograms of pure plutonium hydroxide]]
Plutonium is a reactive metal. In moist air or moist [[argon]], the metal oxidizes rapidly, producing a mixture of [[oxide]]s and [[hydride]]s.<ref name="WISER" /> If the metal is exposed long enough to a limited amount of water vapor, a powdery surface coating of [[Plutonium(IV) oxide|PuO<sub>2</sub>]] is formed.<ref name="WISER" /> Also formed is [[plutonium hydride]] but an excess of water vapor forms only PuO<sub>2</sub>.<ref name="Miner1968p545" />

Plutonium shows enormous, and reversible, reaction rates with pure hydrogen, forming [[plutonium hydride]].<ref name="HeckerPlutonium" /> It also reacts readily with oxygen, forming PuO and PuO<sub>2</sub> as well as intermediate oxides; plutonium oxide fills 40% more volume than plutonium metal. The metal reacts with the [[halogen]]s, giving rise to [[chemical compound|compounds]] with the general formula PuX<sub>3</sub> where X can be [[plutonium(III) fluoride|F]], [[plutonium(III) chloride|Cl]], [[plutonium(III) bromide|Br]] or I and [[Plutonium tetrafluoride|PuF<sub>4</sub>]] is also seen. The following oxyhalides are observed: PuOCl, PuOBr and PuOI. It will react with carbon to form [[Plutonium carbide|PuC]], nitrogen to form [[Plutonium nitride|PuN]] and [[silicon]] to form PuSi<sub>2</sub>.<ref name="CRC2006p4-27" /><ref name="Emsley2001" />

The [[Organometallic chemistry|organometallic]] chemistry of plutonium complexes is typical for [[Organoactinide chemistry|organoactinide]] species; a characteristic example of an organoplutonium compound is [[plutonocene]].<ref name="Greenwood1997p1259" /><ref name="Apostolidis-2017">{{Cite journal |last1=Apostolidis |first1=Christos |last2=Walter |first2=Olaf |last3=Vogt |first3=Jochen |last4=Liebing |first4=Phil |last5=Maron |first5=Laurent |last6=Edelmann |first6=Frank T. |date=2017 |title=A Structurally Characterized Organometallic Plutonium(IV) Complex |journal=Angewandte Chemie International Edition |language=en |volume=56 |issue=18 |pages=5066–5070 |doi=10.1002/anie.201701858 |issn=1521-3773 |pmc=5485009 |pmid=28371148}}</ref> Computational chemistry methods indicate an enhanced [[Covalent bond|covalent]] character in the plutonium-ligand bonding.<ref name="HeckerPlutonium" /><ref name="Apostolidis-2017" />

Powders of plutonium, its hydrides and certain oxides like Pu<sub>2</sub>O<sub>3</sub>
are [[pyrophoricity|pyrophoric]], meaning they can ignite spontaneously at ambient temperature and are therefore handled in an inert, dry atmosphere of nitrogen or argon. Bulk plutonium ignites only when heated above 400&nbsp;°C. Pu<sub>2</sub>O<sub>3</sub> spontaneously heats up and transforms into PuO<sub>2</sub>, which is stable in dry air, but reacts with water vapor when heated.<ref name="NucSafety" />

[[Crucible]]s used to contain plutonium need to be able to withstand its strongly [[redox|reducing]] properties. [[Refractory metals]] such as [[tantalum]] and [[tungsten]] along with the more stable oxides, [[boride]]s, [[carbide]]s, [[nitride]]s and [[silicide]]s can tolerate this. Melting in an [[electric arc furnace]] can be used to produce small ingots of the metal without the need for a crucible.<ref name="Miner1968p542" />

[[Cerium]] is used as a chemical simulant of plutonium for development of containment, extraction, and other technologies.<ref>{{Cite journal |last=Crooks, W. J. |display-authors=etal |date=2002 |title=Low Temperature Reaction of ReillexTM HPQ and Nitric Acid |url=http://sti.srs.gov/fulltext/ms2000068/ms2000068.html |url-status=live |journal=Solvent Extraction and Ion Exchange |volume=20 |issue=4–5 |pages=543–559 |doi=10.1081/SEI-120014371 |s2cid=95081082 |archive-url=https://web.archive.org/web/20110614053034/http://sti.srs.gov/fulltext/ms2000068/ms2000068.html |archive-date=June 14, 2011 |access-date=January 24, 2010}}</ref>

====Electronic structure====
Plutonium is an element in which the [[f shell|5f electrons]] are the transition border between delocalized and localized; it is therefore considered one of the most complex elements.<ref name="physicsworld.com">{{Cite news |last=Dumé, Belle |date=November 20, 2002 |title=Plutonium is also a superconductor |publisher=PhysicsWeb.org |url=http://physicsworld.com/cws/article/news/16443 |url-status=live |access-date=January 24, 2010 |archive-url=https://web.archive.org/web/20120112184014/http://physicsworld.com/cws/article/news/16443 |archive-date=January 12, 2012}}</ref> The anomalous behavior of plutonium is caused by its electronic structure. The energy difference between the 6d and 5f subshells is very low. The size of the 5f shell is just enough to allow the electrons to form bonds within the lattice, on the very boundary between localized and bonding behavior. The proximity of energy levels leads to multiple low-energy electron configurations with near equal energy levels. This leads to competing 5f<sup>n</sup>7s<sup>2</sup> and 5f<sup>n−1</sup>6d<sup>1</sup>7s<sup>2</sup> configurations, which causes the complexity of its chemical behavior. The highly directional nature of 5f orbitals is responsible for directional covalent bonds in molecules and complexes of plutonium.<ref name="HeckerPlutonium" />

===Alloys===
Plutonium can form alloys and intermediate compounds with most other metals. Exceptions include lithium, [[sodium]], [[potassium]], [[rubidium]] and [[caesium]] of the [[alkali metal]]s; and [[magnesium]], calcium, [[strontium]], and barium of the [[alkaline earth metal]]s; and [[europium]] and [[ytterbium]] of the [[rare earth metal]]s.<ref name="Miner1968p545" /> Partial exceptions include the refractory metals [[chromium]], [[molybdenum]], [[niobium]], tantalum, and tungsten, which are soluble in liquid plutonium, but insoluble or only slightly soluble in solid plutonium.<ref name="Miner1968p545" /> Gallium, aluminium, americium, [[scandium]] and cerium can stabilize δ-phase plutonium for room temperature. [[Silicon]], [[indium]], [[zinc]] and [[zirconium]] allow formation of metastable δ state when rapidly cooled. High amounts of [[hafnium]], [[holmium]] and [[thallium]] also allows some retention of the δ phase at room temperature. Neptunium is the only element that can stabilize the α phase at higher temperatures.<ref name="HeckerPlutonium" />

Plutonium alloys can be produced by adding a metal to molten plutonium. If the alloying metal is reductive enough, plutonium can be added in the form of oxides or halides. The δ phase [[plutonium–gallium alloy]] (PGA) and plutonium–aluminium alloy are produced by adding Pu(III) fluoride to molten gallium or aluminium, which has the advantage of avoiding dealing directly with the highly reactive plutonium metal.<ref>{{harvnb|Moody| Hutcheon|Grant|2005|p=169}}</ref>
* '''PGA''' is used for stabilizing the δ phase of plutonium, avoiding the α-phase and α–δ related issues. Its main use is in [[pit (nuclear weapon)|pits]] of [[nuclear weapons design|implosion bombs]].<ref>{{Cite journal |last1=Kolman, D. G. |last2=Colletti, L. P. |name-list-style=amp |date=2009 |title=The aqueous corrosion behavior of plutonium metal and plutonium–gallium alloys exposed to aqueous nitrate and chloride solutions |url=https://books.google.com/books?id=0o4DnYptWdgC&pg=PA71 |url-status=live |journal=ECS Transactions |publisher=Electrochemical Society |volume=16 |issue=52 |page=71 |bibcode=2009ECSTr..16Z..71K |doi=10.1149/1.3229956 |isbn=978-1-56677-751-3 |s2cid=96567022 |archive-url=https://web.archive.org/web/20220316125950/https://books.google.com/books?id=0o4DnYptWdgC&pg=PA71 |archive-date=March 16, 2022 |access-date=December 2, 2020}}</ref>
* '''Plutonium–aluminium''' is an alternative to PGA. It was the original element considered for δ phase stabilization, but its tendency to react with the alpha particles and release neutrons reduces its usability for nuclear weapons. Plutonium–aluminium alloy can be also used as a component of [[nuclear fuel]].<ref>{{harvnb|Hurst|Ward|1956}}</ref>
* '''Plutonium–gallium–cobalt''' alloy (PuCoGa{{sub|5}}) is an [[unconventional superconductor]], showing superconductivity below 18.5&nbsp;K, an order of magnitude higher than the highest between [[heavy fermion]] systems, and has large critical current.<ref name="physicsworld.com" /><ref>{{cite web<!--Citation bot -->|url=http://www.lanl.gov/orgs/mpa/files/mrhighlights/LALP-06-072.pdf|author=Curro, N. J.|title=Unconventional superconductivity in PuCoGa<sub>5</sub>|date=Spring 2006|publisher=Los Alamos National Laboratory|access-date=January 24, 2010|archive-url=https://web.archive.org/web/20110722062226/http://www.lanl.gov/orgs/mpa/files/mrhighlights/LALP-06-072.pdf|archive-date=July 22, 2011|url-status=dead}}</ref>
* '''Plutonium–zirconium''' alloy can be used as [[nuclear fuel]].<ref>McCuaig, Franklin D. "Pu–Zr alloy for high-temperature foil-type fuel" {{US patent|4059439}}, Issued on November 22, 1977</ref>
* '''Plutonium–cerium''' and '''plutonium–cerium–cobalt''' alloys are used as nuclear fuels.<ref>{{harvnb|Jha|2004|p=73}}</ref>
* '''Plutonium–uranium''', with about 15–30&nbsp;mol.% plutonium, can be used as a nuclear fuel for fast breeder reactors. Its [[pyrophoric]] nature and high susceptibility to corrosion to the point of self-igniting or disintegrating after exposure to air require alloying with other components. Addition of aluminium, carbon or copper does not improve disintegration rates markedly, zirconium and iron alloys have better corrosion resistance but they disintegrate in several months in air as well. Addition of titanium and/or zirconium significantly increases the melting point of the alloy.<ref name="Pu1965">{{harvnb|Kay|1965|p=456}}</ref>
* '''Plutonium–uranium–titanium''' and '''plutonium–uranium–zirconium''' were investigated for use as nuclear fuels. The addition of the third element increases corrosion resistance, reduces flammability, and improves ductility, fabricability, strength, and thermal expansion. '''Plutonium–uranium–molybdenum''' has the best corrosion resistance, forming a protective film of oxides, but titanium and zirconium are preferred for physics reasons.<ref name="Pu1965" />
* '''Thorium–uranium–plutonium''' was investigated as a nuclear fuel for fast breeder reactors.<ref name="Pu1965" />

==Occurrence==
Trace amounts of plutonium-238, plutonium-239, plutonium-240, and plutonium-244 can be found in nature. Small traces of plutonium-239, a few [[parts per notation|parts per trillion]], and its decay products are naturally found in some concentrated ores of uranium,<ref name="Miner1968p541" /> such as the [[natural nuclear fission reactor]] in [[Oklo]], [[Gabon]].<ref>{{Cite web |date=2004 |title=Oklo: Natural Nuclear Reactors |url=http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml |archive-url=https://web.archive.org/web/20081020201724/http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml |archive-date=October 20, 2008 |access-date=November 16, 2008 |publisher=U.S. Department of Energy, Office of Civilian Radioactive Waste Management}}</ref> The ratio of plutonium-239 to uranium at the [[Cigar Lake Mine]] uranium deposit ranges from {{val|2.4|e=-12}} to {{val|44|e=-12}}.<ref name="Cigar">{{Cite journal |last1=Curtis |first1=David |last2=Fabryka-Martin |first2=June |last3=Paul |first3=Dixon |last4=Cramer |first4=Jan |date=1999 |title=Nature's uncommon elements: plutonium and technetium |url=https://digital.library.unt.edu/ark:/67531/metadc704244/ |url-status=live |journal=Geochimica et Cosmochimica Acta |volume=63 |issue=2 |pages=275–285 |bibcode=1999GeCoA..63..275C |doi=10.1016/S0016-7037(98)00282-8 |archive-url=https://web.archive.org/web/20210627232349/https://digital.library.unt.edu/ark:/67531/metadc704244/ |archive-date=June 27, 2021 |access-date=June 29, 2019}}</ref> These trace amounts of <sup>239</sup>Pu originate in the following fashion: on rare occasions, <sup>238</sup>U undergoes spontaneous fission, and in the process, the nucleus emits one or two free neutrons with some kinetic energy. When one of these neutrons strikes the nucleus of another <sup>238</sup>U atom, it is absorbed by the atom, which becomes <sup>239</sup>U. With a relatively short half-life, <sup>239</sup>U decays to <sup>239</sup>Np, which decays into <sup>239</sup>Pu.{{sfn|Bernstein|2007|pp=75–77}}<ref>{{Cite journal |last1=Hoffman |first1=D. C. |last2=Lawrence |first2=F. O. |last3=Mewherter |first3=J. L. |last4=Rourke |first4=F. M. |date=1971 |title=Detection of Plutonium-244 in Nature |journal=Nature |volume=234 |issue=5325 |pages=132–134 |bibcode=1971Natur.234..132H |doi=10.1038/234132a0 |s2cid=4283169}}</ref> Finally, exceedingly small amounts of plutonium-238, attributed to the extremely rare [[double beta decay]] of uranium-238, have been found in natural uranium samples.<ref>{{Cite journal |last=Peterson |first=Ivars |date=December 7, 1991 |title=Uranium displays rare type of radioactivity |journal=[[Science News]] |publisher=[[Wiley-Blackwell]] |volume=140 |issue=23 |page=373 |doi=10.2307/3976137 |jstor=3976137}}</ref>

Due to its relatively long half-life of about 80&nbsp;million years, it was suggested that [[plutonium-244]] occurs naturally as a [[primordial nuclide]], but early reports of its detection could not be confirmed.<ref>{{Cite journal |last1=Hoffman |first1=D. C. |last2=Lawrence |first2=F. O. |last3=Mewherter |first3=J. L. |last4=Rourke |first4=F. M. |date=1971 |title=Detection of Plutonium-244 in Nature |journal=Nature |volume=234 |issue=5325 |pages=132–134 |bibcode=1971Natur.234..132H |doi=10.1038/234132a0 |s2cid=4283169 |id=Nr. 34}}</ref> Based on its likely initial abundance in the Solar System, present experiments as of 2022 are likely about an order of magnitude away from detecting live primordial <sup>244</sup>Pu.<ref>{{cite journal |last1=Wu |first1=Yang |last2=Dai |first2=Xiongxin |first3=Shan |last3=Xing |first4=Maoyi |last4=Luo |first5=Marcus |last5=Christl |first6=Hans-Arno |last6=Synal |first7=Shaochun |last7=Hou |date=2022 |title=Direct search for primordial <sup>244</sup>Pu in Bayan Obo bastnaesite |url=http://www.ccspublishing.org.cn/article/doi/10.1016/j.cclet.2022.03.036?pageType=en |journal=Chinese Chemical Letters |volume=33 |issue=7 |pages=3522–3526 |doi=10.1016/j.cclet.2022.03.036 |access-date=29 January 2024 |archive-date=January 29, 2024 |archive-url=https://web.archive.org/web/20240129143208/http://www.ccspublishing.org.cn/article/doi/10.1016/j.cclet.2022.03.036?pageType=en |url-status=dead }}</ref> However, its long half-life ensured its circulation across the solar system before its [[extinct radionuclide|extinction]],<ref name="Turner-2004">{{Cite journal |last1=Turner |first1=Grenville |last2=Harrison |first2=T. Mark |last3=Holland |first3=Greg |last4=Mojzsis |first4=Stephen J. |last5=Gilmour |first5=Jamie |date=2004-01-01 |title=Extinct <sup>244</sup>Pu in Ancient Zircons |url=https://pdfs.semanticscholar.org/3cda/5d558ee8b37160d83d66d7ce0fdb47b3ef75.pdf |url-status=dead |journal=Science |volume=306 |issue=5693 |pages=89–91 |bibcode=2004Sci...306...89T |doi=10.1126/science.1101014 |jstor=3839259 |pmid=15459384 |s2cid=11625563 |archive-url=https://web.archive.org/web/20200211020817/https://pdfs.semanticscholar.org/3cda/5d558ee8b37160d83d66d7ce0fdb47b3ef75.pdf |archive-date=2020-02-11}}</ref> and indeed, evidence of the spontaneous fission of extinct <sup>244</sup>Pu has been found in meteorites.<ref name="Hutcheon-1972">{{Cite journal |last1=Hutcheon |first1=I. D. |last2=Price |first2=P. B. |date=1972-01-01 |title=Plutonium-244 Fission Tracks: Evidence in a Lunar Rock 3.95 Billion Years Old |journal=Science |volume=176 |issue=4037 |pages=909–911 |bibcode=1972Sci...176..909H |doi=10.1126/science.176.4037.909 |jstor=1733798 |pmid=17829301 |s2cid=25831210}}</ref> The former presence of <sup>244</sup>Pu in the early Solar System has been confirmed, since it manifests itself today as an excess of its daughters, either <sup>232</sup>[[thorium|Th]] (from the alpha decay pathway) or [[xenon]] isotopes (from its [[spontaneous fission]]). The latter are generally more useful, because the chemistries of thorium and plutonium are rather similar (both are predominantly tetravalent) and hence an excess of thorium would not be strong evidence that some of it was formed as a plutonium daughter.<ref>{{Cite journal |last1=Kunz |first1=Joachim |last2=Staudacher |first2=Thomas |last3=Allègre |first3=Claude J. |date=1998-01-01 |title=Plutonium-Fission Xenon Found in Earth's Mantle |journal=Science |volume=280 |issue=5365 |pages=877–880 |bibcode=1998Sci...280..877K |doi=10.1126/science.280.5365.877 |jstor=2896480 |pmid=9572726}}</ref> <sup>244</sup>Pu has the longest half-life of all transuranic nuclides and is produced only in the [[r-process]] in [[supernova]]e and colliding [[neutron star]]s; when nuclei are ejected from these events at high speed to reach Earth, <sup>244</sup>Pu alone among transuranic nuclides has a long enough half-life to survive the journey, and hence tiny traces of live interstellar <sup>244</sup>Pu have been found in the deep sea floor. Because <sup>240</sup>Pu also occurs in the [[decay chain]] of <sup>244</sup>Pu, it must thus also be present in [[secular equilibrium]], albeit in even tinier quantities.<ref>{{Cite journal |last1=Wallner |first1=A. |last2=Faestermann |first2=T. |last3=Feige |first3=J. |last4=Feldstein |first4=C. |last5=Knie |first5=K. |last6=Korschinek |first6=G. |last7=Kutschera |first7=W. |last8=Ofan |first8=A. |last9=Paul |first9=M. |last10=Quinto |first10=F. |last11=Rugel |first11=G. |last12=Steiner |first12=P. |date=30 March 2014 |title=Abundance of live <sup>244</sup>Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis |journal=Nature Communications |volume=6 |page=5956 |arxiv=1509.08054 |bibcode=2015NatCo...6.5956W |doi=10.1038/ncomms6956 |pmc=4309418 |pmid=25601158 |s2cid=119286045}}</ref>

Minute traces of plutonium are usually found in the human body due to the 550 atmospheric and underwater [[nuclear testing|nuclear tests]] that have been carried out, and to a small number of major [[list of civilian nuclear accidents|nuclear accidents]].<ref name="Emsley2001">{{harvnb|Emsley|2001|pp=324–329}}</ref> Most atmospheric and underwater nuclear testing was stopped by the [[Limited Test Ban Treaty]] in 1963, which of the nuclear powers was signed and ratified by the United States, United Kingdom and [[Soviet Union]]. France would continue atmospheric nuclear testing until 1974 and China would continue atmospheric nuclear testing until 1980. All subsequent nuclear testing was conducted underground.<ref name=ctbto>{{Cite web |last=<!--Not stated--> |title=Nuclear Testing 1945 - today |url=https://www.ctbto.org/nuclear-testing/history-of-nuclear-testing/nuclear-testing-1945-today/ |url-status=live |archive-url=https://web.archive.org/web/20220207010817/https://www.ctbto.org/nuclear-testing/history-of-nuclear-testing/nuclear-testing-1945-today/ |archive-date=February 7, 2022 |access-date=7 February 2022 |publisher=Comprehensive Test Ban Treaty Organization}}</ref>

==History==
===Discovery===
[[Enrico Fermi]] and a team of scientists at the [[University of Rome La Sapienza|University of Rome]] reported that they had discovered element 94 in 1934.<ref>{{Cite web |last=Holden |first=Norman E. |date=2001 |title=A Short History of Nuclear Data and Its Evaluation |url=http://www.nndc.bnl.gov/content/evaluation.html |url-status=live |archive-url=https://archive.today/20120805065840/http://www.nndc.bnl.gov/content/evaluation.html |archive-date=August 5, 2012 |access-date=January 3, 2009 |website=51st Meeting of the USDOE Cross Section Evaluation Working Group |publisher=National Nuclear Data Center, Brookhaven National Laboratory |location=Upton (NY)}}</ref> Fermi called the element ''[[hesperium]]'' and mentioned it in his Nobel Lecture in 1938.<ref>{{Cite web |last=Fermi |first=Enrico |date=December 12, 1938 |title=Artificial radioactivity produced by neutron bombardment: Nobel Lecture |url=http://www.nobel.se/physics/laureates/1938/fermi-lecture.pdf |url-status=live |archive-url=https://web.archive.org/web/20110805023848/http://nobelprize.org/nobel_prizes/physics/laureates/1938/fermi-lecture.pdf |archive-date=August 5, 2011 |access-date=January 4, 2009 |publisher=Royal Swedish Academy of Sciences}}</ref> The sample actually contained products of [[nuclear fission]], primarily [[barium]] and [[krypton]].<ref>{{Cite web |last=Darden |first=Lindley |date=1998 |title=The Nature of Scientific Inquiry |url=http://www.philosophy.umd.edu/Faculty/LDarden/sciinq/ |url-status=live |archive-url=https://web.archive.org/web/20120817040843/http://www.philosophy.umd.edu/Faculty/LDarden/sciinq/ |archive-date=August 17, 2012 |access-date=January 3, 2008 |publisher=Department of Philosophy, University of Maryland |location=College Park}}</ref> Nuclear fission, discovered in Germany in 1938 by [[Otto Hahn]] and [[Fritz Strassmann]], was unknown at the time.{{sfn|Bernstein|2007|pp=44–52}}

[[File:Glenn Seaborg - 1964.jpg|thumb|upright|[[Glenn T. Seaborg]] and his team at Berkeley were the first to produce plutonium.|alt=Elderly Seaborg in a suit]]
Plutonium (specifically, plutonium-238) was first produced, isolated and then chemically identified between December 1940 and February 1941 by [[Glenn T. Seaborg]], [[Edwin McMillan]], [[Emilio Segrè]], [[Joseph W. Kennedy]], and [[Arthur Wahl]] by deuteron bombardment of uranium in the {{convert|60|in|cm|adj=on|sp=us}} [[cyclotron]] at the [[Berkeley Radiation Laboratory]] at the [[University of California, Berkeley]].<ref>{{Cite web |last=Seaborg, Glenn T. |title=An Early History of LBNL: Elements 93 and 94 |url=http://www.lbl.gov/LBL-PID/Nobelists/Seaborg/65th-anniv/14.html |url-status=live |archive-url=https://web.archive.org/web/20141105083122/http://www2.lbl.gov/LBL-PID/Nobelists/Seaborg/65th-anniv/14.html |archive-date=November 5, 2014 |access-date=September 17, 2008 |publisher=Advanced Computing for Science Department, Lawrence Berkeley National Laboratory}}</ref><ref name="SeaborgStory">{{Cite web |last=Glenn T. Seaborg |date=September 1981 |title=The plutonium story |url=http://www.osti.gov/bridge/purl.cover.jsp?purl=/5808140-l5UMe1/ |url-status=live |archive-url=https://web.archive.org/web/20130516093638/http://www.osti.gov/bridge/purl.cover.jsp?purl=%2F5808140-l5UMe1%2F |archive-date=May 16, 2013 |access-date=March 16, 2022 |publisher=Lawrence Berkeley Laboratory, University of California |id=LBL-13492, DE82 004551}}</ref><ref>E. Segrè, A Mind Always in Motion, University of California Press, 1993, pp 162-169</ref>
Neptunium-238 was created directly by the bombardment but decayed by beta emission with a half-life of a little over two days, which indicated the formation of element 94.<ref name="Emsley2001" /> The first bombardment took place on December 14, 1940, and the new element was first identified through oxidation on the night of February 23–24, 1941.<ref name="SeaborgStory" />

A paper documenting the discovery was prepared by the team and sent to the journal ''[[Physical Review]]'' in March 1941,<ref name="Emsley2001" /> but publication was delayed until a year after the end of [[World War II]] due to security concerns.{{sfn|Seaborg|Seaborg|2001|pp=71–72}} At the [[Cavendish Laboratory]] in [[Cambridge]], Egon Bretscher and [[Norman Feather]] realized that a slow neutron reactor fuelled with uranium would theoretically produce substantial amounts of plutonium-239 as a by-product. They calculated that element 94 would be fissile, and had the added advantage of being chemically different from uranium, and could easily be separated from it.{{sfn|Clark|1961|pp=124–125}}

McMillan had recently named the first transuranic element neptunium after the planet [[Neptune]], and suggested that element 94, being the next element in the series, be named for what was then considered the next planet, [[Pluto]].<ref name="Heiserman1992" />{{efn|group = note|This was not the first time somebody suggested that an element be named "plutonium". A decade after [[barium]] was discovered, a Cambridge University professor suggested it be renamed to "plutonium" because the element was not (as suggested by the [[Greek language|Greek]] root, ''barys'', it was named for) heavy. He reasoned that, since it was produced by the relatively new technique of [[electrolysis]], its name should refer to [[fire]]. Thus he suggested it be named for the Roman god of the underworld, [[Pluto (god)|Pluto]].{{sfn|Heiserman|1992|p=338}} }} [[Nicholas Kemmer]] of the Cambridge team independently proposed the same name, based on the same reasoning as the Berkeley team.{{sfn|Clark|1961|pp=124–125}} Seaborg originally considered the name "plutium", but later thought that it did not sound as good as "plutonium".<ref name="Clark57">{{Cite journal |last1=Clark |first1=David L. |last2=Hobart, David E. |date=2000 |title=Reflections on the Legacy of a Legend: Glenn T. Seaborg, 1912–1999 |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00818011.pdf |url-status=live |journal=Los Alamos Science |volume=26 |pages=56–61, on 57 |archive-url=https://web.archive.org/web/20160603195310/http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818011.pdf |archive-date=June 3, 2016 |access-date=February 15, 2009}}</ref> He chose the letters "Pu" as a joke, in reference to the interjection "P U" to indicate an especially disgusting smell, which passed without notice into the periodic table.{{efn|group = note|As one article puts it, referring to information Seaborg gave in a talk: "The obvious choice for the symbol would have been Pl, but facetiously, Seaborg suggested Pu, like the words a child would exclaim, 'Pee-yoo!' when smelling something bad. Seaborg thought that he would receive a great deal of flak over that suggestion, but the naming committee accepted the symbol without a word."<ref>{{Cite journal |last1=Clark |first1=David L. |last2=Hobart, David E. |date=2000 |title=Reflections on the Legacy of a Legend: Glenn T. Seaborg, 1912–1999 |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00818011.pdf |url-status=live |journal=Los Alamos Science |volume=26 |pages=56–61, on 57 |archive-url=https://web.archive.org/web/20160603195310/http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818011.pdf |archive-date=June 3, 2016 |access-date=February 15, 2009}}</ref>}} Alternative names considered by Seaborg and others were "ultimium" or "extremium" because of the erroneous belief that they had found the last possible [[chemical element|element]] on the [[periodic table]].<ref>{{Cite web |date=1997 |title=Frontline interview with Seaborg |url=https://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/seaborg.html |url-status=live |archive-url=https://web.archive.org/web/20180629155338/https://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/seaborg.html |archive-date=June 29, 2018 |access-date=December 7, 2008 |website=Frontline |publisher=Public Broadcasting Service}}</ref>

Hahn and Strassmann, and independently [[Kurt Starke]], were at this point also working on transuranic elements in Berlin. It is likely that Hahn and Strassmann were aware that plutonium-239 should be fissile. However, they did not have a strong neutron source. Element 93 was reported by Hahn and Strassmann, as well as Starke, in 1942. Hahn's group did not pursue element 94, likely because they were discouraged by McMillan and Abelson's lack of success in isolating it when they had first found element 93. However, since Hahn's group had access to the stronger cyclotron at Paris at this point, they would likely have been able to detect plutonium had they tried, albeit in tiny quantities (a few [[becquerel]]s).<ref name="Germans">{{Cite journal |last1=Winterberg |first1=Friedwardt |last2=Herrmann |first2=Günter |last3=Fodor |first3=Igor |last4=Wolfenstein |first4=Lincoln |last5=Singer |first5=Mark E. |date=1996 |title=More on How Nazi Germany Failed to Develop the Atomic Bomb |journal=Physics Today |volume=49 |issue=1 |pages=11–15, 83 |bibcode=1996PhT....49a..11W |doi=10.1063/1.2807455}}</ref>

===Early research===
[[File:Nh-pluto-in-true-color_2x_JPEG-edit-frame.jpg|thumb|right|The [[dwarf planet]] [[Pluto]], after which plutonium is named]]
The chemistry of plutonium was found to resemble uranium after a few months of initial study.<ref name="Emsley2001" /> Early research was continued at the secret [[Metallurgical Laboratory]] of the [[University of Chicago]]. On August 20, 1942, a trace quantity of this element was isolated and measured for the first time. About 50&nbsp;micrograms of plutonium-239 combined with uranium and fission products was produced and only about 1&nbsp;microgram was isolated.<ref name="Miner1968p541">{{harvnb|Miner|1968|p = 541}}</ref><ref name="seaborg">{{Cite journal |last=Glenn T. Seaborg |year=1977 |title=History of MET Lab Section C-I, April 1942 – April 1943 |url=https://digital.library.unt.edu/ark:/67531/metadc1414500/ |url-status=live |journal=Office of Scientific & Technical Information Technical Reports |publisher=California Univ., Berkeley (USA). Lawrence Berkeley Lab. |doi=10.2172/7110621 |archive-url=https://web.archive.org/web/20200315144213/https://digital.library.unt.edu/ark:/67531/metadc1414500/ |archive-date=March 15, 2020 |access-date=June 29, 2019|doi-access=free }}</ref> This procedure enabled chemists to determine the new element's atomic weight.<ref name="uchicago">{{Cite web |title=Room 405, George Herbert Jones Laboratory |url=http://tps.cr.nps.gov/nhl/detail.cfm?ResourceId=735&ResourceType=Building |url-status=dead |archive-url=https://web.archive.org/web/20080208100011/http://tps.cr.nps.gov/nhl/detail.cfm?ResourceId=735&ResourceType=Building |archive-date=February 8, 2008 |access-date=December 14, 2008 |publisher=National Park Service}}</ref>{{efn|group = note|Room 405 of the [[George Herbert Jones Laboratory]], where the first isolation of plutonium took place, was named a [[National Historic Landmark]] in May 1967.}} On December 2, 1942, on a racket court under the west grandstand at the University of Chicago's Stagg Field, researchers headed by [[Enrico Fermi]] achieved the first self-sustaining chain reaction in a graphite and uranium pile known as [[Chicago Pile-1|CP-1]]. Using theoretical information garnered from the operation of CP-1, DuPont constructed an air-cooled experimental production reactor, known as [[X-10 Graphite Reactor|X-10]], and a pilot chemical separation facility at Oak Ridge. The separation facility, using methods developed by Glenn T. Seaborg and a team of researchers at the Met Lab, removed plutonium from uranium irradiated in the X-10 reactor. Information from CP-1 was also useful to Met Lab scientists designing the water-cooled plutonium production reactors for Hanford. Construction at the site began in mid-1943.<ref name="FAP">{{Cite web |title=Periodic Table of Elements |url=http://periodic.lanl.gov/94.shtml |url-status=live |archive-url=https://web.archive.org/web/20190212165622/https://periodic.lanl.gov/94.shtml |archive-date=February 12, 2019 |access-date=September 15, 2015 |publisher=Los Alamos National Laboratory}}</ref>

In November 1943 some [[plutonium trifluoride]] was reduced to create the first sample of plutonium metal: a few micrograms of metallic beads.<ref name="Miner1968p541" /> Enough plutonium was produced to make it the first synthetically made element to be visible with the unaided eye.<ref name="Miner1968p540">{{harvnb|Miner|1968|p = 540}}</ref>

The nuclear properties of plutonium-239 were also studied; researchers found that when it is hit by a neutron it breaks apart (fissions) by releasing more neutrons and energy. These neutrons can hit other atoms of plutonium-239 and so on in an exponentially fast chain reaction. This can result in an explosion large enough to destroy a city if enough of the isotope is concentrated to form a [[critical mass]].<ref name="Emsley2001" />

During the early stages of research, animals were used to study the effects of radioactive substances on health. These studies began in 1944 at the University of California at Berkeley's Radiation Laboratory and were conducted by Joseph G. Hamilton. Hamilton was looking to answer questions about how plutonium would vary in the body depending on exposure mode (oral ingestion, inhalation, absorption through skin), retention rates, and how plutonium would be fixed in tissues and distributed among the various organs. Hamilton started administering soluble microgram portions of plutonium-239 compounds to rats using different valence states and different methods of introducing the plutonium (oral, intravenous, etc.). Eventually, the lab at Chicago also conducted its own plutonium injection experiments using different animals such as mice, rabbits, fish, and even dogs. The results of the studies at Berkeley and Chicago showed that plutonium's physiological behavior differed significantly from that of radium. The most alarming result was that there was significant deposition of plutonium in the liver and in the "actively metabolizing" portion of bone. Furthermore, the rate of plutonium elimination in the excreta differed between species of animals by as much as a factor of five. Such variation made it extremely difficult to estimate what the rate would be for human beings.<ref name="FAY">{{Cite web |title=Plutonium |url=http://www.atomicheritage.org/history/plutonium |url-status=live |archive-url=https://web.archive.org/web/20190506105952/https://www.atomicheritage.org/history/plutonium |archive-date=May 6, 2019 |access-date=September 15, 2015 |publisher=Atomic Heritage Foundation}}</ref>

===Production during the Manhattan Project===
During World War II the U.S. government established the [[Manhattan Project]], for developing an atomic bomb. The three primary research and production sites of the project were the plutonium production facility at what is now the [[Hanford Site]]; the [[uranium enrichment]] facilities at [[Oak Ridge, Tennessee]]; and the weapons research and design lab, now known as [[Los Alamos National Laboratory]], LANL.<ref>{{Cite web |title=Site Selection |url=http://www.lanl.gov/history/road/siteselection.shtml |url-status=live |archive-url=https://web.archive.org/web/20110913013719/http://www.lanl.gov/history/road/siteselection.shtml |archive-date=September 13, 2011 |access-date=December 23, 2008 |website=LANL History |publisher=Los Alamos National Laboratory |location=Los Alamos, New Mexico}}</ref>

[[File:Hanford B Reactor.jpg|thumb|The Hanford [[B Reactor]] face under construction—the first plutonium-production reactor|alt=Tall square industrial room seen from above. Its cement walls have metal ladders and meshes, and a dozen people work on the floor.]]
[[Image:Hanford N Reactor adjusted.jpg|thumb|right|The [[Hanford site]] represents two-thirds of U.S. high-level [[radioactive waste]] by volume. Nuclear reactors line the riverbank at the Hanford Site along the [[Columbia River]] in January 1960.|alt=Aerial shot of Hanford]]

The first production reactor that made {{sup|239}}Pu was the [[X-10 Graphite Reactor]]. It went online in 1943 and was built at a facility in Oak Ridge that later became the [[Oak Ridge National Laboratory]].<ref name="Emsley2001" />{{efn|group = note|During the Manhattan Project, plutonium was also often referred to as simply "49": the number 4 was for the last digit in 94 (atomic number of plutonium), and 9 was for the last digit in plutonium-239, the weapons-grade fissile isotope used in nuclear bombs.<ref>{{Cite journal |last=Hammel |first=E. F. |date=2000 |title=The taming of "49"&nbsp; – Big Science in little time. Recollections of Edward F. Hammel, In: Cooper N.G. Ed. Challenges in Plutonium Science |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00818010.pdf |url-status=live |journal=Los Alamos Science |volume=26 |issue=1 |pages=2–9 |archive-url=https://web.archive.org/web/20170120125028/https://fas.org/sgp/othergov/doe/lanl/pubs/00818010.pdf |archive-date=January 20, 2017 |access-date=February 15, 2009}}
:{{Cite journal
|last = Hecker
|first = S. S.
|date = 2000
|title = Plutonium: an historical overview. In: Challenges in Plutonium Science
|journal = Los Alamos Science
|volume = 26
|issue = 1
|pages = 1–2
|url = https://fas.org/sgp/othergov/doe/lanl/pubs/number26.htm
|access-date = February 15, 2009
|archive-date = January 18, 2017
|archive-url = https://web.archive.org/web/20170118083808/https://fas.org/sgp/othergov/doe/lanl/pubs/number26.htm
|url-status = live
}}</ref>}}

In January 1944, workers laid the foundations for the first chemical separation building, T Plant located in 200-West. Both the T Plant and its sister facility in 200-West, the U Plant, were completed by October. (U Plant was used only for training during the Manhattan Project.) The separation building in 200-East, B Plant, was completed in February 1945. The second facility planned for 200-East was canceled. Nicknamed Queen Marys by the workers who built them, the separation buildings were awesome canyon-like structures 800 feet long, 65 feet wide, and 80 feet high containing forty process pools. The interior had an eerie quality as operators behind seven feet of concrete shielding manipulated remote control equipment by looking through television monitors and periscopes from an upper gallery. Even with massive concrete lids on the process pools, precautions against radiation exposure were necessary and influenced all aspects of plant design.<ref name="FAP" />

On April 5, 1944, [[Emilio Segrè]] at Los Alamos received the first sample of reactor-produced plutonium from Oak Ridge.<ref name="AtomicTimeline">{{Cite web |last=Sublette |first=Carey |title=Atomic History Timeline 1942–1944 |url=http://www.atomicheritage.org/index.php?option=com_content&task=view&id=288&Itemid=202 |url-status=live |archive-url=https://web.archive.org/web/20090104020055/http://www.atomicheritage.org/index.php?option=com_content&task=view&id=288&Itemid=202 |archive-date=January 4, 2009 |access-date=December 22, 2008 |publisher=Atomic Heritage Foundation |location=Washington (DC)}}</ref> Within ten days, he discovered that reactor-bred plutonium had a higher concentration of {{sup|240}}Pu than cyclotron-produced plutonium. {{sup|240}}Pu has a high spontaneous fission rate, raising the overall background neutron level of the plutonium sample.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp = 235–239}} The original [[gun-type bomb|gun-type]] plutonium weapon, code-named "[[Thin Man nuclear bomb|Thin Man]]", had to be abandoned as a result—the increased number of spontaneous neutrons meant that nuclear pre-detonation ([[fizzle (nuclear test)|fizzle]]) was likely.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240–242}}

The entire plutonium weapon design effort at Los Alamos was soon changed to the more complicated implosion device, code-named "[[Fat Man]]". In an implosion bomb, plutonium is compressed to high density with [[explosive lens]]es—a technically more daunting task than the simple gun-type bomb, but necessary for a plutonium bomb. Uranium, by contrast, can be used with either method.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240–242}}

Construction of the Hanford [[B Reactor]], the first industrial-sized nuclear reactor for the purposes of material production, was completed in March 1945. B Reactor produced the fissile material for the plutonium weapons used during World War II.{{efn|group=note|The American Society of Mechanical Engineers (ASME) established B Reactor as a National Historic Mechanical Engineering Landmark in September 1976.{{sfn|Wahlen|1989|p=1}} In August 2008, B Reactor was designated a U.S. [[National Historic Landmark]].<ref>{{Cite web |date=August 29, 2008 |title=Weekly List Actions |url=http://www.nps.gov/history/nr/listings/20080829.HTM |url-status=live |archive-url=https://web.archive.org/web/20081031143513/http://www.nps.gov/history/nr/listings/20080829.HTM |archive-date=October 31, 2008 |access-date=August 30, 2008 |publisher=National Park Service}}</ref>}} B, D and F were the initial reactors built at Hanford, and six additional plutonium-producing reactors were built later at the site.<ref name="100B">{{harvnb|Wahlen|1989|p=iv, 1}}</ref>

By the end of January 1945, the highly purified plutonium underwent further concentration in the completed chemical isolation building, where remaining impurities were removed successfully. Los Alamos received its first plutonium from Hanford on February 2. While it was still by no means clear that enough plutonium could be produced for use in bombs by the war's end, Hanford was by early 1945 in operation. Only two years had passed since Col. [[Franklin Matthias]] first set up his temporary headquarters on the banks of the Columbia River.<ref name="FAP" />

According to [[Kate Brown (professor)|Kate Brown]], the plutonium production plants at Hanford and [[Mayak]] in Russia, over a period of four decades, "both released more than 200 million curies of radioactive isotopes into the surrounding environment—twice the amount expelled in the [[Chernobyl disaster]] in each instance".<ref name="katebr" /> Most of this [[radioactive contamination]] over the years were part of normal operations, but unforeseen accidents did occur and plant management kept this secret, as the pollution continued unabated.<ref name="katebr">{{Cite web |last=Lindley |first=Robert |date=2013 |title=Kate Brown: Nuclear "Plutopias" the Largest Welfare Program in American History |url=http://hnn.us/article/153096 |url-status=live |archive-url=https://web.archive.org/web/20190503112316/http://hnn.us/article/153096 |archive-date=May 3, 2019 |access-date=December 19, 2013 |website=History News Network}}</ref>

In 2004, a safe was discovered during excavations of a burial trench at the [[Hanford nuclear site]]. Inside the safe were various items, including a large glass bottle containing a whitish slurry which was subsequently identified as the oldest sample of weapons-grade plutonium known to exist. Isotope analysis by [[Pacific Northwest National Laboratory]] indicated that the plutonium in the bottle was manufactured in the X-10 Graphite Reactor at Oak Ridge during 1944.<ref>{{Cite news |last=Rincon |first=Paul |date=March 2, 2009 |title=BBC NEWS – Science & Environment – US nuclear relic found in bottle |work=BBC News |url=http://news.bbc.co.uk/2/hi/science/nature/7918618.stm |url-status=live |access-date=March 2, 2009 |archive-url=https://web.archive.org/web/20090302235654/http://news.bbc.co.uk/2/hi/science/nature/7918618.stm |archive-date=March 2, 2009}}</ref><ref>{{Cite journal |last=Gebel |first=Erika |date=2009 |title=Old plutonium, new tricks |journal=Analytical Chemistry |volume=81 |issue=5 |page=1724 |doi=10.1021/ac900093b |doi-access=free}}</ref><ref>{{Cite journal |last1=Schwantes |first1=Jon M. |last2=Matthew Douglas |last3=Steven E. Bonde |last4=James D. Briggs |last5=Orville T. Farmer |last6=Lawrence R. Greenwood |last7=Elwood A. Lepel |last8=Christopher R. Orton |last9=John F. Wacker |last10=Andrzej T. Luksic |display-authors=4 |date=2009 |title=Nuclear archeology in a bottle: Evidence of pre-Trinity U.S. weapons activities from a waste burial site |journal=Analytical Chemistry |volume=81 |issue=4 |pages=1297–1306 |doi=10.1021/ac802286a |pmid=19152306}}</ref>

===Trinity and Fat Man atomic bombs===
[[File:Fission bomb assembly methods.svg|upright=1.25|thumb|Due to the presence of {{sup|240}}Pu in reactor-bred plutonium, the implosion design was developed for "[[Fat Man]]" and "[[Trinity test|Trinity]]".|alt=Two diagrams of weapon assembly. Top: "gun-type assembly method": an elliptical shell encloses conventional explosives on the left, whose detonation pushes sub-critical pieces of uranium-235 together on the right. Bottom: "implosion assembly method": a spherical shell encloses eight high-explosive charges which upon detonation compress a plutonium charge in the core.]]

The first atomic bomb test, codenamed "[[Trinity test|Trinity]] "and detonated on July 16, 1945, near [[Alamogordo, New Mexico]], used plutonium as its fissile material.<ref name="Miner1968p541" /> The implosion design of "[[Trinity (nuclear test)#"The Gadget"|Gadget]]", as the Trinity device was codenamed, used conventional explosive lenses to compress a sphere of plutonium into a supercritical mass, which was simultaneously showered with neutrons from [[Urchin (detonator)|"Urchin"]], an initiator made of [[polonium]] and [[beryllium]] ([[neutron source]]: [[Neutron source#Small sized devices|(α, n) reaction]]).<ref name="Emsley2001" /> Together, these ensured a runaway chain reaction and explosion. The weapon weighed over 4 [[tonne]]s, though it had just 6&nbsp;kg of plutonium.<ref>{{Cite web |last=Sublette |first=Carey |date=July 3, 2007 |title=8.1.1 The Design of Gadget, Fat Man, and "Joe 1" (RDS-1) |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html#nfaq8.1.1 |access-date=January 4, 2008 |website=Nuclear Weapons Frequently Asked Questions, edition 2.18 |publisher=The Nuclear Weapon Archive}}</ref> About 20% of the plutonium in the Trinity weapon, fissioned; releasing an energy equivalent to about 20,000 tons of TNT.<ref name="yield">{{Cite web |last=Malik |first=John |date=September 1985 |title=The Yields of the Hiroshima and Nagasaki Explosions |url=https://fas.org/sgp/othergov/doe/lanl/docs1/00313791.pdf |url-status=live |archive-url=https://web.archive.org/web/20090224204106/https://fas.org/sgp/othergov/doe/lanl/docs1/00313791.pdf |archive-date=February 24, 2009 |access-date=February 15, 2009 |publisher=Los Alamos |page=Table VI |id=LA-8819}}</ref>{{efn|group = note|The efficiency calculation is based on the fact that 1&nbsp;kg of plutonium-239 (or uranium-235) fissioning results in an energy release of approximately 17 [[kiloton|kt]], leading to a rounded estimate of 1.2&nbsp;kg plutonium actually fissioned to produce the 20 kt yield.<ref>On the figure of 1&nbsp;kg = 17 kt, see {{Cite web |last=Garwin |first=Richard |author-link=Richard Garwin |date=October 4, 2002 |title=Proliferation of Nuclear Weapons and Materials to State and Non-State Actors: What It Means for the Future of Nuclear Power |url=https://fas.org/rlg/PNWM_UMich.pdf |url-status=live |archive-url=https://web.archive.org/web/20090224204150/http://www.fas.org/rlg/PNWM_UMich.pdf |archive-date=February 24, 2009 |access-date=January 4, 2009 |website=University of Michigan Symposium |publisher=Federation of American Scientists}}</ref>}}

An identical design was used in "Fat Man", dropped on [[Nagasaki]], [[Japan]], on August 9, 1945, killing 35,000–40,000 people and destroying 68%–80% of war production at Nagasaki.{{sfn|Sklar|1984|pp=22–29}} Only after the announcement of the first atomic bombs was the existence and name of plutonium made known to the public by the Manhattan Project's [[Smyth Report]].{{sfn|Bernstein|2007|p=70}}

===Cold War use and waste===
{{See also|Reactor-grade plutonium}}
Large stockpiles of [[weapons-grade plutonium]] were built up by both the [[Soviet Union]] and the United States during the [[Cold War]]. The U.S. reactors at Hanford and the [[Savannah River Site]] in South Carolina produced 103&nbsp;tonnes,<ref>{{Cite web |date=2001 |title=Historic American Engineering Record: B Reactor (105-B Building) |url=https://fas.org/sgp/othergov/doe/pu50yb.html#ZZ13 |url-status=live |archive-url=https://web.archive.org/web/20081226090634/http://www.fas.org/sgp/othergov/doe/pu50yb.html#ZZ13 |archive-date=December 26, 2008 |access-date=December 24, 2008 |publisher=U.S. Department of Energy |page=110 |id=DOE/RL-2001-16 |location=Richland}}</ref> and an estimated 170&nbsp;tonnes of military-grade plutonium was produced in the USSR.<ref>{{Cite conference |last=Cochran |first=Thomas B. |date=1997 |title=Safeguarding nuclear weapons-usable materials in Russia |url=http://docs.nrdc.org/nuclear/nuc_06129701a_185.pdf |conference=International Forum on Illegal Nuclear Traffic |location=Washington (DC) |publisher=Natural Resources Defense Council, Inc. |archive-url=https://web.archive.org/web/20130705053828/http://docs.nrdc.org/nuclear/files/nuc_06129701a_185.pdf |archive-date=July 5, 2013 |access-date=December 21, 2008}}</ref>{{efn|group = note|Much of this plutonium was used to make the fissionable cores of a type of thermonuclear weapon employing the [[Teller–Ulam design]]. These so-called 'hydrogen bombs' are a variety of nuclear weapon that use a fission bomb to trigger the [[nuclear fusion]] of heavy [[hydrogen]] isotopes. Their destructive yield is commonly in the millions of tons of TNT equivalent compared with the thousands of tons of TNT equivalent of fission-only devices.{{sfn|Emsley|2001}} }} Each year about 20&nbsp;tonnes of the element is still produced as a by-product of the [[nuclear power]] industry.<ref name="CRC2006p4-27">{{harvnb|Lide|2006|pp = 4–27}}</ref> As much as 1000&nbsp;tonnes of plutonium may be in storage with more than 200&nbsp;tonnes of that either inside or extracted from nuclear weapons.<ref name="Emsley2001" />
[[SIPRI]] estimated the world plutonium [[stockpile]] in 2007 as about 500 tonnes, divided equally between weapon and civilian stocks.{{sfn|Stockholm International Peace Research Institute|2007|p=567}}

Radioactive contamination at the [[Rocky Flats Plant]] primarily resulted from two major plutonium fires in 1957 and 1969. Much lower concentrations of radioactive isotopes were released throughout the operational life of the plant from 1952 to 1992. Prevailing winds from the plant carried airborne contamination south and east, into populated areas northwest of Denver. The contamination of the Denver area by plutonium from the fires and other sources was not publicly reported until the 1970s. According to a 1972 study coauthored by [[Edward Martell]], "In the more densely populated areas of Denver, the Pu contamination level in surface soils is several times fallout", and the plutonium contamination "just east of the Rocky Flats plant ranges up to hundreds of times that from nuclear tests".<ref name="Poet1972">{{Cite journal |last1=Poet |first1=S. E. |last2=Martell, EA |date=October 1972 |title=Plutonium-239 and americium-241 contamination in the Denver area. |journal=Health Physics |volume=23 |issue=4 |pages=537–48 |doi=10.1097/00004032-197210000-00012 |pmid=4634934 |s2cid=26296070}}</ref> As noted by [[Carl J. Johnson|Carl Johnson]] in [[Ambio]], "Exposures of a large population in the Denver area to plutonium and other radionuclides in the exhaust plumes from the plant date back to 1953."<ref name="Johnson1981">{{Cite journal |last=Johnson |first=C. J. |date=October 1981 |title=Cancer Incidence in an area contaminated with radionuclides near a nuclear installation |journal=Ambio |volume=10 |issue=4 |pages=176–182 |jstor=4312671 |pmid=7348208}} Reprinted in {{cite journal |pmid=7348208 | volume=78 | issue=10 | title=Cancer Incidence in an area contaminated with radionuclides near a nuclear installation | date=Oct 1981 | journal=Colo Med | pages=385–92| last1=Johnson | first1=C. J }}</ref> Weapons production at the Rocky Flats plant was halted after a combined [[Federal Bureau of Investigation|FBI]] and [[United States Environmental Protection Agency|EPA]] raid in 1989 and years of protests. The plant has since been shut down, with its buildings demolished and completely removed from the site.<ref name="FWSmainpage">{{Cite web |title=Rocky Flats National Wildlife Refuge |url=http://www.fws.gov/rockyflats/ |url-status=live |archive-url=https://web.archive.org/web/20200409011048/http://www.fws.gov/rockyflats/ |archive-date=April 9, 2020 |access-date=2 July 2013 |publisher=U.S. Fish & Wildlife Service}}</ref>

In the U.S., some plutonium extracted from dismantled nuclear weapons is melted to form glass logs of [[plutonium oxide]] that weigh two&nbsp;tonnes.<ref name="Emsley2001" /> The glass is made of [[borosilicate]]s mixed with [[cadmium]] and [[gadolinium]].{{efn|group = note|[[Gadolinium zirconium oxide]] ({{chem|Gd|2|Zr|2|O|7}}) has been studied because it could hold plutonium for up to 30&nbsp;million years.{{sfn|Emsley|2001}} }} These logs are planned to be encased in [[stainless steel]] and stored as much as {{convert|4|km|0|abbr=on}} underground in bore holes that will be back-filled with [[concrete]].<ref name="Emsley2001" /> The U.S. planned to store plutonium in this way at the [[Yucca Mountain nuclear waste repository]], which is about {{convert|100|mi|km|sp=us}} north-east of [[Las Vegas, Nevada]].<ref>{{Cite web |last=Press Secretary |date=July 23, 2002 |title=President Signs Yucca Mountain Bill |url=https://georgewbush-whitehouse.archives.gov/news/releases/2002/07/20020723-2.html |archive-url=https://web.archive.org/web/20080306193653/http://georgewbush-whitehouse.archives.gov/news/releases/2002/07/20020723-2.html |archive-date=March 6, 2008 |access-date=February 9, 2015 |publisher=Office of the Press Secretary, White House |location=Washington (DC)}}</ref>

On March 5, 2009, [[United States Secretary of Energy|Energy Secretary]] [[Steven Chu]] told a Senate hearing "the Yucca Mountain site no longer was viewed as an option for storing reactor waste".<ref>{{Cite web |last=Hebert |first=H. Josef |date=March 6, 2009 |title=Nuclear waste won't be going to Nevada's Yucca Mountain, Obama official says |url=http://www.chicagotribune.com/news/nationworld/chi-nuke-yucca_frimar06,0,2557502.story |url-status=dead |archive-url=https://web.archive.org/web/20110324074934/http://www.chicagotribune.com/news/nationworld/chi-nuke-yucca_frimar06,0,2557502.story |archive-date=March 24, 2011 |access-date=2011-03-17 |website=Chicago Tribune |page=4}}</ref> Starting in 1999, military-generated nuclear waste is being entombed at the [[Waste Isolation Pilot Plant]] in New Mexico.

In a Presidential Memorandum dated January 29, 2010, President Obama established the [[Blue Ribbon Commission on America's Nuclear Future]].<ref name="About the Commission">{{Cite web |title=About the Commission |url=http://brc.gov/index.php?q=page%2Fabout-commission |url-status=dead |archive-url=https://web.archive.org/web/20110621063744/http://brc.gov/index.php?q=page%2Fabout-commission |archive-date=June 21, 2011}}</ref> In their final report the Commission put forth recommendations for developing a comprehensive strategy to pursue, including:<ref name="Blue Ribbon Commission on America's Nuclear Future">{{Cite web |last=Blue Ribbon Commission on America’s Nuclear Future |title=Disposal Subcommittee Report to the Full Commission |url=https://curie.ornl.gov/system/files/documents/not%20yet%20assigned/disposal_report_updated_final.pdf |url-status=dead |archive-url=https://web.archive.org/web/20170125203730/https://curie.ornl.gov/system/files/documents/not%20yet%20assigned/disposal_report_updated_final.pdf |archive-date=January 25, 2017 |access-date=February 26, 2017}}</ref>

: "Recommendation #1: The United States should undertake an integrated nuclear waste management program that leads to the timely development of one or more permanent deep geological facilities for the safe disposal of spent fuel and high-level nuclear waste".<ref name="Blue Ribbon Commission on America's Nuclear Future" />

===Medical experimentation===
{{See also|Human radiation experiments|Albert Stevens}}
During and after the end of World War II, scientists working on the Manhattan Project and other nuclear weapons research projects conducted studies of the effects of plutonium on laboratory animals and human subjects.<ref name="Injection" /> Animal studies found that a few milligrams of plutonium per kg of tissue is a lethal dose.<ref name="PuHealth" /><!-- Note: page 78 -->

For human subjects, this involved injecting solutions typically containing 5 micrograms (μg) of plutonium into hospital patients thought to be either terminally ill, or to have a life expectancy of less than ten years either due to age or chronic disease.<ref name="Injection" /> This was reduced to 1 μg in July 1945 after animal studies found that the way plutonium distributes itself in bones is more dangerous than [[radium]].<ref name="PuHealth">{{Cite journal |last=Voelz |first=George L. |date=2000 |title=Plutonium and Health: How great is the risk? |journal=Los Alamos Science |location=Los Alamos (NM) |publisher=Los Alamos National Laboratory |issue=26 |pages=78–79}}</ref> Most of the subjects, [[Eileen Welsome]] says, were poor, powerless, and sick.<ref name="rc">{{Cite journal |last=Longworth |first=R. C. |date=November–December 1999 |title=Injected! Book review: The Plutonium Files: America's Secret Medical Experiments in the Cold War. |url=http://intl-bos.sagepub.com/content/55/6/58.full.pdf+html |url-status=dead |journal=[[The Bulletin of the Atomic Scientists]] |volume=55 |issue=6 |pages=58–61 |doi=10.2968/055006016 |archive-url=https://archive.today/20130105021134/http://intl-bos.sagepub.com/content/55/6/58.full.pdf+html |archive-date=January 5, 2013}}</ref>

In 1945–47, eighteen human test subjects were injected with plutonium without [[informed consent]]. The tests were used to create diagnostic tools to determine the uptake of plutonium in the body in order to develop safety standards for working with plutonium.<ref name="Injection">{{Cite journal |last1=Moss |first1=William |last2=Eckhardt, Roger |date=1995 |title=The Human Plutonium Injection Experiments |url=http://library.lanl.gov/cgi-bin/getfile?23-09.pdf |url-status=live |journal=Los Alamos Science |publisher=Los Alamos National Laboratory |volume=23 |pages=188, 205, 208, 214 |archive-url=https://web.archive.org/web/20090114152623/http://library.lanl.gov/cgi-bin/getfile?23-09.pdf |archive-date=January 14, 2009 |access-date=June 6, 2006}}</ref> [[Ebb Cade]] was an unwilling participant in medical experiments that involved injection of 4.7 μg of plutonium on 10 April 1945 at [[Oak Ridge, Tennessee]].<ref>Moss, William, and Roger Eckhardt. (1995). "The human plutonium injection experiments." Los Alamos Science. 23: 177–233.</ref><ref>Openness, DOE. (June 1998). Human Radiation Experiments: ACHRE Report. Chapter 5: The Manhattan district Experiments; the first injection. Washington, DC. Superintendent of Documents US Government Printing Office.</ref> This experiment was under the supervision of [[Harold Hodge]].<ref>AEC no. UR-38, 1948 Quarterly Technical Report</ref> Other experiments directed by the [[United States Atomic Energy Commission]] and the Manhattan Project continued into the 1970s. ''[[The Plutonium Files]]'' chronicles the lives of the subjects of the secret program by naming each person involved and discussing the ethical and medical research conducted in secret by the scientists and doctors. The episode is now considered to be a serious breach of [[medical ethics]] and of the [[Hippocratic Oath]].<ref>{{Cite journal |last=Yesley |first=Michael S. |date=1995 |title='Ethical Harm' and the Plutonium Injection Experiments |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00326649.pdf |url-status=live |journal=Los Alamos Science |volume=23 |pages=280–283 |archive-url=https://web.archive.org/web/20090224204033/http://www.fas.org/sgp/othergov/doe/lanl/pubs/00326649.pdf |archive-date=February 24, 2009 |access-date=February 15, 2009}}</ref>

The government covered up most of these actions until 1993, when President [[Bill Clinton]] ordered a change of policy and federal agencies then made available relevant records. The resulting investigation was undertaken by the president's [[Advisory Committee on Human Radiation Experiments]], and it uncovered much of the material about plutonium research on humans. The committee issued a controversial 1995 report which said that "wrongs were committed" but it did not condemn those who perpetrated them.<ref name="rc" />

==Applications==
===Explosives===
[[File:Nagasakibomb.jpg|thumb|upright|The [[Atomic bombings of Hiroshima and Nagasaki|atomic bomb dropped on Nagasaki, Japan]], in 1945 had a plutonium core.|alt=Photo of a nuclear mushroom cloud with a gray stem and white cap]]
{{sup|239}}Pu is a key fissile component in nuclear weapons, due to its ease of fission and availability. Encasing the bomb's [[plutonium pit]] in a [[nuclear weapon design|tamper]] (a layer of dense material) decreases the [[critical mass]] by [[neutron reflector|reflecting escaping neutrons]] back into the plutonium core. This reduces the critical mass from 16&nbsp;kg to 10&nbsp;kg, which is a sphere with a diameter of about {{convert|10|cm|0|sp=us}}.{{sfn|Martin|2000|p=532}} This critical mass is about a third of that for uranium-235.<ref name="Heiserman1992" />

The Fat Man plutonium bombs used explosive compression of plutonium to obtain significantly higher density than normal, combined with a central neutron source to begin the reaction and increase efficiency. Thus only 6&nbsp;kg of plutonium was needed for an [[nuclear weapon yield|explosive yield]] equivalent to 20 kilotons of TNT.<ref name="yield" /><ref name="FASdesign">{{Cite web |date=1998 |title=Nuclear Weapon Design |url=https://fas.org/nuke/intro/nuke/design.htm |url-status=dead |archive-url=https://web.archive.org/web/20081226091803/https://fas.org/nuke/intro/nuke/design.htm |archive-date=December 26, 2008 |access-date=December 7, 2008 |publisher=[[Federation of American Scientists]]}}</ref> Hypothetically, as little as 4&nbsp;kg of plutonium—and maybe even less—could be used to make a single atomic bomb using very sophisticated assembly designs.<ref name="FASdesign" />

===Mixed oxide fuel===
{{main|Nuclear reprocessing|Weapons-grade nuclear material}}

[[Spent nuclear fuel]] from normal [[light water reactor]]s contains plutonium, but it is a mixture of [[plutonium-242]], 240, 239 and 238. The mixture is not sufficiently enriched for efficient nuclear weapons, but can be used once as [[MOX fuel]].<ref name="MOX" /> Accidental neutron capture causes the amount of plutonium-242 and 240 to grow each time the plutonium is irradiated in a reactor with low-speed "thermal" neutrons, so that after the second cycle, the plutonium can only be consumed by [[fast neutron reactor]]s. If fast neutron reactors are not available (the normal case), excess plutonium is usually discarded, and forms one of the longest-lived components of nuclear waste. The desire to consume this plutonium and other [[transuranic]] fuels and reduce the radiotoxicity of the waste is the usual reason nuclear engineers give to make fast neutron reactors.{{sfn|Till|Chang|2011|pp=254–256}}

The most common chemical process, [[PUREX]] (''P''lutonium–''UR''anium ''EX''traction), [[nuclear reprocessing|reprocesses]] spent nuclear fuel to extract plutonium and uranium which can be used to form a mixed oxide (MOX) fuel for reuse in nuclear reactors. Weapons-grade plutonium can be added to the fuel mix. MOX fuel is used in [[light water reactor]]s and consists of 60&nbsp;kg of plutonium per tonne of fuel; after four years, three-quarters of the plutonium is burned (turned into other elements).<ref name="Emsley2001" /> MOX fuel has been in use since the 1980s, and is widely used in Europe.<ref name="MOX">{{Cite web |date=2006 |title=Mixed Oxide (MOX) Fuel |url=http://www.world-nuclear.org/info/inf29.html |url-status=live |archive-url=https://web.archive.org/web/20130301173649/http://www.world-nuclear.org/info/inf29.html |archive-date=March 1, 2013 |access-date=December 14, 2008 |publisher=World Nuclear Association |location=London (UK)}}</ref> [[Breeder reactor]]s are specifically designed to create more fissionable material than they consume.{{sfn|Till|Chang|2011|p=15}}

MOX fuel improves total burnup. A fuel rod is reprocessed after three years of use to remove waste products, which by then account for 3% of the total weight of the rods.<ref name="Emsley2001" /> Any uranium or plutonium isotopes produced during those three years are left and the rod goes back into production.{{efn|group = note|Breakdown of plutonium in a spent nuclear fuel rod: plutonium-239 (~58%), 240 (24%), 241 (11%), 242 (5%), and 238 (2%).{{sfn|Emsley|2001}} }} The presence of up to 1% gallium per mass in weapons-grade [[plutonium-gallium alloy|plutonium alloy]] has the potential to interfere with long-term operation of a light water reactor.<ref>{{Cite journal |last=Besmann |first=Theodore M. |date=2005 |title=Thermochemical Behavior of Gallium in Weapons-Material-Derived Mixed-Oxide Light Water Reactor (LWR) Fuel |url=https://zenodo.org/record/1230603 |url-status=live |journal=Journal of the American Ceramic Society |volume=81 |issue=12 |pages=3071–3076 |doi=10.1111/j.1151-2916.1998.tb02740.x |archive-url=https://web.archive.org/web/20200317210240/https://zenodo.org/record/1230603 |archive-date=March 17, 2020 |access-date=June 29, 2019}}<!-- {{doi|10.1007/BF02881277}}--></ref>

Plutonium recovered from spent reactor fuel poses little proliferation hazard, because of excessive contamination with non-fissile plutonium-240 and plutonium-242. Separation of the isotopes is not feasible. A dedicated reactor operating on very low [[burnup]] (hence minimal exposure of newly formed plutonium-239 to additional neutrons which causes it to be transformed to heavier isotopes of plutonium) is generally required to produce material suitable for use in efficient [[nuclear weapons]]. While "weapons-grade" plutonium is defined to contain at least 92% plutonium-239 (of the total plutonium), the United States have managed to detonate an [[reactor-grade plutonium nuclear test|under-20Kt device]] using plutonium believed to contain only about 85% plutonium-239, so called '"fuel-grade" plutonium.<ref name="inf15" /> The "reactor-grade" plutonium produced by a regular LWR burnup cycle typically contains less than 60% Pu-239, with up to 30% parasitic Pu-240/Pu-242, and 10–15% fissile Pu-241.<ref name="inf15" /> It is unknown if a device using plutonium obtained from reprocessed civil nuclear waste can be detonated, however such a device could hypothetically fizzle and spread radioactive materials over a large urban area. The [[IAEA]] conservatively classifies plutonium of all isotopic vectors as "direct-use" material, that is, "nuclear material that can be used for the manufacture of nuclear explosives components without transmutation or further enrichment".<ref name="inf15">{{Cite web |date=March 2009 |title=Plutonium |url=http://www.world-nuclear.org/info/inf15.html |url-status=live |archive-url=https://web.archive.org/web/20100330221426/http://www.world-nuclear.org/info/inf15.html |archive-date=March 30, 2010 |access-date=February 28, 2010 |publisher=World Nuclear Association}}</ref>

===Power and heat source===
[[File:Plutonium pellet.jpg|thumb|A glowing cylinder of {{sup|238}}PuO{{sub|2}}|alt=Glowing cylinder of plutonium oxide standing in a circular pit]]
[[File:Fueling of the MSL MMRTG 001.jpg|thumb|The {{sup|238}}PuO{{sub|2}} radioisotope thermoelectric generator of the [[Curiosity (rover)|''Curiosity'' rover]]|alt=Glowing graphite cube containing plutonium-238 oxide]]
Plutonium-238 has a half-life of 87.74&nbsp;years.<ref>{{Cite web |title=Science for the Critical Masses: How Plutonium Changes with Time |url=http://www.ieer.org/ensec/no-3/puchange.html |url-status=live |archive-url=https://web.archive.org/web/20120214121455/http://www.ieer.org/ensec/no-3/puchange.html |archive-date=February 14, 2012 |access-date=July 2, 2010 |publisher=Institute for Energy and Environmental Research}}</ref> It emits a large amount of [[thermal energy]] with low levels of both [[gamma ray]]s/[[photon]]s and neutrons.<ref name="pumper">{{Cite journal |date=2005 |title=From heat sources to heart sources: Los Alamos made material for plutonium-powered pumper |url=http://arq.lanl.gov/source/orgs/nmt/nmtdo/AQarchive/05spring/heart.html |url-status=dead |journal=Actinide Research Quarterly |location=Los Alamos |publisher=Los Alamos National Laboratory |issue=1 |archive-url=https://web.archive.org/web/20130216225324/http://arq.lanl.gov/source/orgs/nmt/nmtdo/AQarchive/05spring/heart.html |archive-date=February 16, 2013 |access-date=February 15, 2009}}</ref> Being an alpha emitter, it combines high energy radiation with low penetration and thereby requires minimal shielding. A sheet of paper can be used to shield against the alpha particles from {{sup|238}}Pu. One [[kilogram]] of the isotope generates about 570 watts of heat.<ref name="Heiserman1992" /><ref name="pumper" />

These characteristics make it well-suited for electrical power generation for devices that must function without direct maintenance for timescales approximating a human lifetime. It is therefore used in [[radioisotope thermoelectric generator]]s and [[radioisotope heater unit]]s such as those in the ''[[Cassini–Huygens|Cassini]]'',<ref name="Solar">{{Cite web |date=December 6, 1996 |title=Why the Cassini Mission Cannot Use Solar Arrays |url=http://saturn.jpl.nasa.gov/spacecraft/safety/solar.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150226085238/http://saturn.jpl.nasa.gov/spacecraft/safety/solar.pdf |archive-date=February 26, 2015 |access-date=March 21, 2014 |publisher=NASA/JPL}}</ref> ''[[Voyager program|Voyager]]'', ''[[Galileo (spacecraft)|Galileo]]'' and ''[[New Horizons]]''<ref>St. Fleur, Nicholas, [https://www.nytimes.com/interactive/projects/cp/summer-of-science-2015/latest/new-horizons-pluto-plutonium "The Radioactive Heart of the New Horizons Spacecraft to Pluto"] {{Webarchive|url=https://web.archive.org/web/20170109170629/http://www.nytimes.com/interactive/projects/cp/summer-of-science-2015/latest/new-horizons-pluto-plutonium |date=January 9, 2017 }}, New York ''Times'', August 7, 2015. The "craft's 125-pound generator [is] called the General Purpose Heat Source-Radioisotope Thermoelectric Generator. [It] was stocked with 24 pounds of plutonium that produced about 240 watts of electricity when it left Earth in 2006, according to Ryan Bechtel, an engineer from the Department of Energy who works on space nuclear power. During the Pluto flyby the battery produced 202 watts, Mr. Bechtel said. The power will continue to decrease as the metal decays, but there is enough of it to command the probe for another 20 years, according to Curt Niebur, a NASA program scientist on the New Horizons mission." Retrieved 2015-08-10.</ref> space probes, and the ''[[Curiosity (rover)|Curiosity]]''<ref>{{Cite magazine |last=Mosher |first=Dave |date=September 19, 2013 |title=NASA's Plutonium Problem Could End Deep-Space Exploration |magazine=[[Wired (magazine)|Wired]] |url=https://www.wired.com/2013/09/plutonium-238-problem/all/ |url-status=live |access-date=February 5, 2015 |archive-url=https://web.archive.org/web/20150208033956/http://www.wired.com/2013/09/plutonium-238-problem/all |archive-date=February 8, 2015}}</ref> and ''[[Perseverance (rover)|Perseverance]]'' ([[Mars 2020]]) [[Mars rover]]s.

The twin ''Voyager'' spacecraft were launched in 1977, each containing a 500 watt plutonium power source. Over 30 years later, each source still produces about 300 watts which allows limited operation of each spacecraft.<ref>{{Cite web |date=June 11, 2014 |title=Voyager-Spacecraft Lifetime |url=http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html |url-status=live |archive-url=https://web.archive.org/web/20071027080026/http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html |archive-date=October 27, 2007 |access-date=February 5, 2015 |publisher=[[Jet Propulsion Laboratory]]}}</ref> An earlier version of the same technology powered five [[ALSEP|Apollo Lunar Surface Experiment Packages]], starting with [[Apollo 12]] in 1969.<ref name="Emsley2001" />

{{sup|238}}Pu has also been used successfully to power artificial heart [[pacemaker]]s, to reduce the risk of repeated surgery.<ref>{{Cite journal |last1=Venkateswara Sarma Mallela |last2=V. Ilankumaran |last3=N.Srinivasa Rao |name-list-style=amp |date=2004 |title=Trends in Cardiac Pacemaker Batteries |journal=Indian Pacing Electrophysiol |volume=4 |issue=4 |pages=201–212 |pmc=1502062 |pmid=16943934}}</ref><ref>{{Cite web |title=Plutonium Powered Pacemaker (1974) |url=https://www.orau.org/health-physics-museum/collection/miscellaneous/pacemaker.html |url-status=live |archive-url=https://web.archive.org/web/20211029173352/https://www.orau.org/health-physics-museum/collection/miscellaneous/pacemaker.html |archive-date=October 29, 2021 |access-date=October 11, 2021 |publisher=Oak Ridge Associated Universities}}</ref> It has been largely replaced by lithium-based [[primary cell]]s, but {{as of|2003|lc=on}} there were somewhere between 50 and 100 plutonium-powered pacemakers still implanted and functioning in living patients in the United States.<ref>{{Cite web |date=2021 |title=Plutonium Powered Pacemaker (1974) |url=https://www.orau.org/health-physics-museum/collection/miscellaneous/pacemaker.html |url-status=live |archive-url=https://web.archive.org/web/20211029173352/https://www.orau.org/health-physics-museum/collection/miscellaneous/pacemaker.html |archive-date=October 29, 2021 |access-date=October 11, 2021 |publisher=Orau.org |location=Oak Ridge}}</ref> By the end of 2007, the number of plutonium-powered pacemakers was reported to be down to just nine.<ref>{{Cite web |date=December 19, 2007 |title=Nuclear pacemaker still energized after 34 years |url=https://uk.reuters.com/article/health-heart-pacemaker-dc/nuclear-pacemaker-still-energized-after-34-years-idUKN1960427320071219 |url-status=dead |archive-url=https://web.archive.org/web/20180109090610/https://uk.reuters.com/article/health-heart-pacemaker-dc/nuclear-pacemaker-still-energized-after-34-years-idUKN1960427320071219 |archive-date=January 9, 2018 |access-date=March 14, 2019}}</ref> {{sup|238}}Pu was studied as a way to provide supplemental heat to [[scuba diving]].<ref>{{Cite report |url=http://www.dtic.mil/docs/citations/AD0708680 |title=SEALAB III – Diver's Isotopic Swimsuit-Heater System |last1=Bayles |first1=John J. |last2=Taylor, Douglas |date=1970 |publisher=Naval Civil Engineering Lab |location=Port Hueneme |id=AD0708680 |archive-url=https://web.archive.org/web/20200312232220/http://www.dtic.mil/docs/citations/AD0708680 |archive-date=March 12, 2020 |url-status=dead}}</ref> {{sup|238}}Pu mixed with beryllium is used to generate neutrons for research purposes.<ref name="Emsley2001" />

==Precautions==
{{See also|Plutonium in the environment}}

===Toxicity===
There are two aspects to the harmful effects of plutonium: radioactivity and [[heavy metal poisoning]]. Plutonium compounds are radioactive and accumulate in [[bone marrow]]. Contamination by plutonium oxide has resulted from [[lists of nuclear disasters and radioactive incidents|nuclear disasters and radioactive incidents]], including military nuclear accidents where nuclear weapons have burned.<ref>{{Cite web |date=November 2010 |title=Toxicological Profile for Plutonium |url=http://www.atsdr.cdc.gov/toxprofiles/tp143.pdf |url-status=live |archive-url=https://web.archive.org/web/20120528223403/http://www.atsdr.cdc.gov/ToxProfiles/tp143.pdf |archive-date=May 28, 2012 |access-date=February 9, 2015 |publisher=U.S. Department of Health and Human Services, [[Agency for Toxic Substances and Disease Registry]] (ATSDR)}}</ref> Studies of the effects of these smaller releases, as well as of the widespread radiation poisoning sickness and death following the [[atomic bombings of Hiroshima and Nagasaki]], have provided considerable information regarding the dangers, symptoms and prognosis of [[radiation poisoning]], which in the case of the [[Hibakusha|Japanese survivors]] was largely unrelated to direct plutonium exposure.<ref>{{Cite journal |last=Little |first=M. P. |date=June 2009 |title=Cancer and non-cancer effects in Japanese atomic bomb survivors |journal=J Radiol Prot |volume=29 |issue=2A |pages=A43–59 |bibcode=2009JRP....29...43L |doi=10.1088/0952-4746/29/2A/S04 |pmid=19454804 |s2cid=29868078}}</ref>

The decay of plutonium, releases three types of [[ionizing radiation]]: [[Alpha decay|alpha]] (α), [[Beta particle|beta]] (β), and [[Gamma ray|gamma]] (γ). Either acute or longer-term exposure carries a danger of [[ionizing radiation#Biological effects|serious health outcomes]] including [[radiation sickness]], [[genetic damage]], [[cancer]], and death. The danger increases with the amount of exposure.<ref name="Emsley2001" /> α-radiation can travel only a short distance and cannot travel through the outer, dead layer of human skin. β-radiation can penetrate human skin, but cannot go all the way through the body. γ-radiation can go all the way through the body.<ref>{{Cite web |title=Plutonium, CAS ID #: 7440-07-5 |url=https://wwwn.cdc.gov/TSP/index.aspx?toxid=119 |url-status=live |archive-url=https://web.archive.org/web/20150205000126/http://www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=119 |archive-date=February 5, 2015 |access-date=February 5, 2015 |publisher=[[Centers for Disease Control and Prevention]] (CDC) [[Agency for Toxic Substances and Disease Registry]]}}</ref>
Even though α radiation cannot penetrate the skin, ingested or inhaled plutonium does irradiate internal organs.<ref name="Emsley2001" /> α-particles generated by inhaled plutonium have been found to cause lung cancer in a cohort of European nuclear workers.<ref>{{Cite journal |last1=Grellier |first1=James |last2=Atkinson |first2=Will |last3=Bérard |first3=Philippe |last4=Bingham |first4=Derek |last5=Birchall |first5=Alan |last6=Blanchardon |first6=Eric |last7=Bull |first7=Richard |last8=Guseva Canu |first8=Irina |last9=Challeton-de Vathaire |first9=Cécile |last10=Cockerill |first10=Rupert |last11=Do |first11=Minh T |last12=Engels |first12=Hilde |last13=Figuerola |first13=Jordi |last14=Foster |first14=Adrian |last15=Holmstock |first15=Luc |date=2017 |title=Risk of lung cancer mortality in nuclear workers from internal exposure to alpha particle-emitting radionuclides |journal=Epidemiology |volume=28 |issue=5 |pages=675–684 |doi=10.1097/EDE.0000000000000684 |pmc=5540354 |pmid=28520643 |last16=Hurtgen |first16=Christian |last17=Laurier |first17=Dominique |last18=Puncher |first18=Matthew |last19=Riddell |first19=Tony |last20=Samson |first20=Eric |last21=Thierry-Chef |first21=Isabelle |last22=Tirmarche |first22=Margot |last23=Vrijheid |first23=Martine |last24=Cardis |first24=Elisabeth}}</ref> The [[skeleton]], where plutonium accumulates, and the [[liver]], where it collects and becomes concentrated, are at risk.<ref name="Miner1968p545" /> Plutonium is not absorbed into the body efficiently when ingested; only 0.04% of plutonium oxide is absorbed after ingestion.<ref name="Emsley2001" /> Plutonium absorbed by the body is excreted very slowly, with a [[biological half-life]] of 200 years.<ref>{{Cite web |title=Radiological control technical training |url=http://hss.energy.gov/NuclearSafety/techstds/standard/hdbk1122-04/part9of9.pdf |archive-url=https://web.archive.org/web/20070630190114/http://hss.energy.gov/NuclearSafety/techstds/standard/hdbk1122-04/part9of9.pdf |archive-date=June 30, 2007 |access-date=December 14, 2008 |publisher=U.S. Department of Energy}}</ref> Plutonium passes only slowly through cell membranes and intestinal boundaries, so absorption by ingestion and incorporation into bone structure proceeds very slowly.<ref name="CohenMyth">{{Cite web |last=Cohen |first=Bernard L. |author-link=Bernard Cohen (physicist) |title=The Myth of Plutonium Toxicity |url=http://russp.org/BLC-3.html |url-status=dead |archive-url=https://web.archive.org/web/20110826115232/http://russp.org/BLC-3.html |archive-date=August 26, 2011}}</ref><ref>{{Cite journal |last=Cohen |first=Bernard L. |date=May 1977 |title=Hazards from Plutonium Toxicity |journal=The Radiation Safety Journal: Health Physics |volume=32 |issue=5 |pages=359–379 |doi=10.1097/00004032-197705000-00003 |pmid=881333 |s2cid=46325265 }}</ref> [[Donald Mastick]] accidentally swallowed a small amount of [[plutonium(III) chloride]], which was detectable for the next thirty years of his life, but appeared to suffer no ill effects.<ref>{{Cite book |last=Welsome |first=Eileen |title=The Plutonium Files: America's Secret Medical Experiments in the Cold War |publisher=The Dial Press |year=1999 |isbn=0-385-31402-7 |location=New York |pages=15–19 |oclc=537755781}}</ref>

Plutonium is more dangerous if inhaled than if ingested. The risk of [[lung cancer]] increases once the total radiation [[equivalent dose|dose equivalent]] of inhaled plutonium exceeds 400 [[sievert|mSv]].<ref name="Brown">{{Cite journal |last1=Brown |first1=Shannon C. |last2=Margaret F. Schonbeck |last3=David McClure |display-authors=etal |date=July 2004 |title=Lung cancer and internal lung doses among plutonium workers at the Rocky Flats Plant: a case-control study |journal=American Journal of Epidemiology |publisher=Oxford Journals |volume=160 |issue=2 |pages=163–172 |doi=10.1093/aje/kwh192 |pmid=15234938 |doi-access=free}}</ref> The U.S. Department of Energy estimates that the lifetime cancer risk from inhaling 5,000 plutonium particles, each about 3&nbsp;μm wide, is 1% over the background U.S. average.<ref name="world-nuclear">{{Cite web |date=2001 |title=ANL human health fact sheet—plutonium |url=http://www.evs.anl.gov/pub/doc/Plutonium.pdf |archive-url=https://web.archive.org/web/20130216175757/http://www.evs.anl.gov/pub/doc/Plutonium.pdf |archive-date=February 16, 2013 |access-date=June 16, 2007 |publisher=Argonne National Laboratory}}</ref> Ingestion or inhalation of large amounts may cause acute radiation poisoning and possibly death. However, no human being is known to have died because of inhaling or ingesting plutonium, and many people have measurable amounts of plutonium in their bodies.<ref name="inf15" />

The "[[hot particle]]" theory in which a particle of plutonium dust irradiates a localized spot of lung tissue is not supported by mainstream research—such particles are more mobile than originally thought and toxicity is not measurably increased due to particulate form.<ref name="CohenMyth" /> When inhaled, plutonium can pass into the bloodstream. Once in the bloodstream, plutonium moves throughout the body and into the bones, liver, or other body organs. Plutonium that reaches body organs generally stays in the body for decades and continues to expose the surrounding tissue to radiation and thus may cause cancer.<ref name="EPA">{{Cite web |title=Radiation Protection, Plutonium: What does plutonium do once it gets into the body? |url=http://www.epa.gov/radiation/radionuclides/plutonium.html |url-status=live |archive-url=https://web.archive.org/web/20110316055920/http://www.epa.gov/radiation/radionuclides/plutonium.html |archive-date=March 16, 2011 |access-date=March 15, 2011 |publisher=U.S. Environmental Protection Agency}}</ref>

A commonly cited quote by [[Ralph Nader]] states that a pound of plutonium dust spread into the atmosphere would be enough to kill 8&nbsp;billion people.<ref>{{Cite web |title=Did Ralph Nader say that a pound of plutonium could cause 8 billion cancers? |url=http://skeptics.stackexchange.com/questions/18236/did-ralph-nader-say-that-a-pound-of-plutonium-could-cause-8-billion-cancers |url-status=live |archive-url=https://web.archive.org/web/20131103060512/http://skeptics.stackexchange.com/questions/18236/did-ralph-nader-say-that-a-pound-of-plutonium-could-cause-8-billion-cancers |archive-date=November 3, 2013 |access-date=January 3, 2013}}</ref> This was disputed by [[Bernard Cohen (physicist)|Bernard Cohen]], an opponent of the generally accepted [[linear no-threshold model]] of radiation toxicity. Cohen estimated that one pound of plutonium could kill no more than 2&nbsp;million people by inhalation, so that the toxicity of plutonium is roughly equivalent with that of [[nerve gas]].<ref name="Cohen-13">{{Cite web |last=Bernard L. Cohen |title=The Nuclear Energy Option, Chapter 13, Plutonium and Bombs |url=http://www.phyast.pitt.edu/~blc/book/chapter13.html |url-status=live |archive-url=https://web.archive.org/web/20130721142313/http://www.phyast.pitt.edu/~blc/book/chapter13.html |archive-date=July 21, 2013 |access-date=March 28, 2011}} (Online version of Cohen's book ''The Nuclear Energy Option'' (Plenum Press, 1990) {{ISBN|0-306-43567-5}}).</ref>

Several populations of people who have been exposed to plutonium dust (e.g. people living down-wind of Nevada test sites, Nagasaki survivors, nuclear facility workers, and "terminally ill" patients injected with Pu in 1945–46 to study Pu metabolism) have been carefully followed and analyzed. Cohen found these studies inconsistent with high estimates of plutonium toxicity, citing cases such as [[Albert Stevens]] who survived into old age after being injected with plutonium.<ref name="CohenMyth" /> "There were about 25 workers from Los Alamos National Laboratory who inhaled a considerable amount of plutonium dust during 1940s; according to the hot-particle theory, each of them has a 99.5% chance of being dead from lung cancer by now, but there has not been a single lung cancer among them."<ref name="Cohen-13" /><ref>{{Cite journal |last=Voelz |first=G. L. |date=1975 |title=What We Have Learned About Plutonium from Human Data |url=http://journals.lww.com/health-physics/Abstract/1975/10000/What_We_Have_Learned_about_Plutonium_from_Human.11.aspx |url-status=live |journal=The Radiation Safety Journal Health Physics |volume=29 |issue=4 |pages=551–561 |doi=10.1097/00004032-197510000-00011 |pmid=1205858 |s2cid=11705537 |archive-url=https://web.archive.org/web/20170816062504/http://journals.lww.com/health-physics/Abstract/1975/10000/What_We_Have_Learned_about_Plutonium_from_Human.11.aspx |archive-date=August 16, 2017 |access-date=December 29, 2009}}</ref>

===Marine toxicity===
Plutonium is known to enter the marine environment by dumping of waste or accidental leakage from nuclear plants. Though the highest concentrations of plutonium in marine environments are found in sediments, the complex biogeochemical cycle of plutonium means it is also found in all other compartments.<ref name="Bioaccumulation and distribution of">{{Cite journal |last1=Skwarzec |first1=B |last2=Struminska |first2=D |last3=Borylo |first3=A |date=2001 |title=Bioaccumulation and distribution of plutonium in fish from Gdansk Bay |journal=Journal of Environmental Radioactivity |volume=55 |issue=2 |pages=167–178 |doi=10.1016/s0265-931x(00)00190-9 |pmid=11398376|bibcode=2001JEnvR..55..167S }}</ref> For example, various zooplankton species that aid in the [[nutrient cycle]] will consume the element on a daily basis. The complete excretion of ingested plutonium by zooplankton makes their defecation an extremely important mechanism in the scavenging of plutonium from surface waters.<ref>{{Cite journal |last1=Baxter |first1=M |last2=Fowler |first2=S |last3=Povined |first3=P |date=1995 |title=Observations on plutonium in the oceans |journal=Applied Radiation and Isotopes |volume=46 |issue=11 |pages=1213–1223 |doi=10.1016/0969-8043(95)00163-8|bibcode=1995AppRI..46.1213B }}</ref> However, those zooplankton that succumb to predation by larger organisms may become a transmission vehicle of plutonium to fish.

In addition to consumption, fish can also be exposed to plutonium by their distribution around the globe. One study investigated the effects of transuranium elements ([[plutonium-238]], [[plutonium-239]], [[plutonium-240]]) on various fish living in the [[Chernobyl exclusion zone|Chernobyl Exclusion Zone]] (CEZ). Results showed that a proportion of female perch in the CEZ displayed either a failure or delay in maturation of the gonads.<ref>{{Cite journal |last1=Lerebours |first1=A |last2=Gudkov |first2=D |last3=Nagorskaya |first3=L |last4=Kaglyan |first4=A |last5=Rizewski |first5=V |last6=Leshchenko |first6=A |date=2018 |title=Impact of Environmental Radiation on the Health and Reproductive Status of Fish from Chernobyl |journal=Environmental Science & Technology |volume=52 |issue=16 |pages=9442–9450 |bibcode=2018EnST...52.9442L |doi=10.1021/acs.est.8b02378 |pmid=30028950 |doi-access=free}}</ref> Similar studies found large accumulations of plutonium in the respiratory and digestive organs of cod, flounder and herring.<ref name="Bioaccumulation and distribution of" />

Plutonium toxicity is just as detrimental to larvae of fish in nuclear waste areas. Undeveloped eggs have a higher risk than developed adult fish exposed to the element in these waste areas. Oak Ridge National Laboratory displayed that carp and minnow embryos raised in solutions containing plutonium did not hatch; eggs that hatched displayed significant abnormalities when compared to control developed embryos.<ref>{{Cite journal |last1=Till |first1=John E. |last2=Kaye |first2=S. V. |last3=Trabalka |first3=J. R. |date=1976 |title=The Toxicity of Uranium and Plutonium to the Developing Embryos of Fish |url=https://www.osti.gov/servlets/purl/7344946 |url-status=live |journal=Oak Ridge National Laboratory |pages=187 |doi=10.2172/7344946 |archive-url=https://web.archive.org/web/20220316130037/https://www.osti.gov/biblio/7344946 |archive-date=March 16, 2022 |access-date=November 20, 2020|doi-access=free }}</ref> It revealed that higher concentrations of plutonium have been found to cause issues in marine fauna exposed to the element.

===Criticality potential===
[[File:Partially-reflected-plutonium-sphere.jpeg|thumb|A sphere of plutonium surrounded by neutron-reflecting [[tungsten carbide]] blocks in a re-enactment of Harry Daghlian's 1945 experiment|alt=A stack of square metal plates with a side about 10 inches. In the 3-inch hole in the top plate there is a gray metal ball simulating Pu.]]
Care must be taken to avoid the accumulation of amounts of plutonium which approach critical mass, particularly because plutonium's critical mass is only a third of that of uranium-235.<ref name="Heiserman1992" /> A critical mass of plutonium emits lethal amounts of neutrons and [[gamma ray]]s.<ref name="Miner1968p546">{{harvnb|Miner|1968|p = 546}}</ref> Plutonium in solution is more likely to form a critical mass than the solid form due to [[neutron moderator|moderation]] by the hydrogen in water.{{dubious|date=November 2020}}<ref name="CRC2006p4-27" />

[[Criticality accident]]s have occurred, sometimes killing people. Careless handling of [[tungsten carbide]] bricks around a 6.2&nbsp;kg plutonium sphere resulted in a fatal dose of radiation at Los Alamos on August 21, 1945, when scientist [[Harry Daghlian]] received a dose estimated at 5.1&nbsp;sievert (510&nbsp;[[Roentgen equivalent man|rem]]) and died 25&nbsp;days later.<ref>{{Cite web |last=Roark |first=Kevin N. |date=2000 |title=Criticality accidents report issued |url=http://www.lanl.gov/news/index.php/fuseaction/home.story/story_id/1054/view/print |archive-url=https://web.archive.org/web/20081008180945/http://lanl.gov/news/index.php/fuseaction/home.story/story_id/1054/view/print |archive-date=October 8, 2008 |access-date=November 16, 2008 |publisher=Los Alamos National Laboratory |location=Los Alamos (NM)}}</ref>{{sfn|Hunner|2004|p=85}} Nine months later, another Los Alamos scientist, [[Louis Slotin]], died from a similar accident involving a beryllium reflector and the same plutonium core (the "[[demon core]]") that had previously killed Daghlian.<ref>{{Cite web |title=Raemer Schreiber |url=http://www.lanl.gov/history/people/R_Schreiber.shtml |archive-url=https://web.archive.org/web/20130103180527/http://www.lanl.gov/history/people/R_Schreiber.shtml |archive-date=January 3, 2013 |access-date=November 16, 2008 |website=Staff Biographies |publisher=Los Alamos National Laboratory |location=Los Alamos}}</ref>

In December 1958, during a process of purifying plutonium at Los Alamos, a critical mass formed in a mixing vessel, which killed chemical operator [[Cecil Kelley]]. Other [[nuclear and radiation accidents|nuclear accidents]] have occurred in the Soviet Union, Japan, the United States, and many other countries.{{sfn|McLaughlin|Monahan|Pruvost|2000|p=17}}

===Flammability===
Metallic plutonium is a fire hazard, especially if finely divided. In a moist environment, plutonium forms [[hydrides]] on its surface, which are pyrophoric and may ignite in air at room temperature. Plutonium expands up to 70% in volume as it oxidizes and thus may break its container.<ref name="NucSafety" /> The radioactivity of the burning material is another hazard. [[Magnesium oxide]] sand is probably the most effective material for extinguishing a plutonium fire. It cools the burning material, acting as a [[heat sink]], and also blocks off oxygen. Special precautions are necessary to store or handle plutonium in any form; generally a dry [[inert gas]] atmosphere is required.<ref name="NucSafety">{{Cite web |date=1994 |title=Primer on Spontaneous Heating and Pyrophoricity – Pyrophoric Metals – Plutonium |url=http://www.hss.energy.gov/NuclearSafety/techstds/standard/hdbk1081/hbk1081d.html#ZZ281 |url-status=dead |archive-url=https://web.archive.org/web/20070428220410/http://www.hss.energy.gov/NuclearSafety/techstds/standard/hdbk1081/hbk1081d.html |archive-date=April 28, 2007 |publisher=U.S. Department of Energy, Office of Nuclear Safety, Quality Assurance and Environment |location=Washington (DC)}}</ref>{{efn|group=note|There was a major plutonium-initiated fire at the [[Rocky Flats Plant]] near [[Boulder, Colorado]] in 1969.<ref>{{Cite web |last1=Albright |first1=David |last2=O'Neill |first2=Kevin |date=1999 |title=The Lessons of Nuclear Secrecy at Rocky Flats |url=http://www.isis-online.org/publications/usfacilities/Rfpbrf.html |archive-url=https://web.archive.org/web/20080708220510/http://www.isis-online.org/publications/usfacilities/Rfpbrf.html |archive-date=July 8, 2008 |access-date=December 7, 2008 |website=ISIS Issue Brief |publisher=Institute for Science and International Security (ISIS)}}</ref>}}

==Transportation==
===Land and sea===
The usual transport of plutonium is through the more stable plutonium oxide in a sealed package. A typical transport consists of one truck carrying one protected shipping container, holding a number of packages with a total weight varying from 80 to 200&nbsp;kg of plutonium oxide. A sea shipment may consist of several containers, each holding a sealed package.<ref>{{Cite web |title=Transport of Radioactive Materials |url=http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Transport/Transport-of-Radioactive-Materials/ |url-status=live |archive-url=https://web.archive.org/web/20150205234207/http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Transport/Transport-of-Radioactive-Materials/ |archive-date=February 5, 2015 |access-date=February 6, 2015 |publisher=World Nuclear Association}}</ref> The U.S. [[Nuclear Regulatory Commission]] dictates that it must be solid instead of powder if the contents surpass 0.74&nbsp;[[Becquerel|TBq]] (20&nbsp;[[Curie (unit)|curies]]) of radioactivity.<ref>{{Cite web |title=§ 71.63 Special requirement for plutonium shipments |url=https://www.nrc.gov/reading-rm/doc-collections/cfr/part071/part071-0063.html |url-status=live |archive-url=https://web.archive.org/web/20150205233706/http://www.nrc.gov/reading-rm/doc-collections/cfr/part071/part071-0063.html |archive-date=February 5, 2015 |access-date=February 6, 2015 |publisher=[[United States Nuclear Regulatory Commission]]}}</ref> In 2016, the ships [[MV Pacific Egret|''Pacific Egret'']]<ref>{{Cite web |title=Pacific Egret |url=http://www.pntl.co.uk/our-fleet/pntl-ships/pacific-egret-2010/ |url-status=live |archive-url=https://web.archive.org/web/20160420142328/http://www.pntl.co.uk/our-fleet/pntl-ships/pacific-egret-2010/ |archive-date=April 20, 2016 |access-date=22 March 2016}}</ref> and ''Pacific Heron'' of Pacific Nuclear Transport Ltd. transported 331&nbsp;kg (730&nbsp;lbs) of plutonium to a United States government facility in [[Savannah River Site|Savannah River]], [[South Carolina]].<ref>{{Cite news |last=Yamaguchi |first=Mari |title=Two British ships arrive in Japan to carry plutonium to US |url=http://phys.org/news/2016-03-british-ships-japan-plutonium.html |url-status=live |access-date=22 March 2016 |archive-url=https://web.archive.org/web/20160323052617/http://phys.org/news/2016-03-british-ships-japan-plutonium.html |archive-date=March 23, 2016}}</ref><ref>{{Cite news |title=Two British ships arrive in Japan to transport plutonium for storage in U.S. |url=http://www.japantimes.co.jp/news/2016/03/21/national/two-british-ships-arrive-in-japan-to-transport-plutonium-for-storage-in-u-s/ |url-status=live |access-date=22 March 2016 |archive-url=https://web.archive.org/web/20160324014231/http://www.japantimes.co.jp/news/2016/03/21/national/two-british-ships-arrive-in-japan-to-transport-plutonium-for-storage-in-u-s |archive-date=March 24, 2016}}</ref>

===Air===
U.S. Government air transport regulations permit the transport of plutonium by air, subject to restrictions on other dangerous materials carried on the same flight, packaging requirements, and stowage in the rearmost part of the aircraft.<ref>{{Cite web |title=Part 175.704 Plutonium shipments |url=http://law.justia.com/cfr/title49/49-2.1.1.3.10.html#49:2.1.1.3.10.3.25.9 |url-status=live |archive-url=https://web.archive.org/web/20120427120248/http://law.justia.com/cfr/title49/49-2.1.1.3.10.html#49:2.1.1.3.10.3.25.9 |archive-date=April 27, 2012 |access-date=August 1, 2012 |website=Code of Federal Regulations 49 — Transportation}}</ref>

In 2012, media revealed that plutonium has been flown out of Norway on commercial [[passenger airline]]s—around every other year—including one time in 2011.<ref name="klassekampen1">{{Cite web |last=Av Ida Søraunet Wangberg og Anne Kari Hinna |title=Klassekampen : Flyr plutonium med rutefly |url=http://klassekampen.no/60502/article/item/null/flyr-plutonium-med-rutefly |url-status=live |archive-url=https://web.archive.org/web/20120802235151/http://www.klassekampen.no/60502/article/item/null/flyr-plutonium-med-rutefly |archive-date=August 2, 2012 |access-date=August 13, 2012 |publisher=Klassekampen.no}}</ref> Regulations permit a plane to transport 15 grams of fissionable material.<ref name="klassekampen1" /> Such plutonium transportation is without problems, according to a senior advisor (''seniorrådgiver'') at [[Statens strålevern]].<ref name="klassekampen1" />

==Notes==
===Footnotes===
{{Reflist|group=note}}

===Citations===
{{Reflist}}

==References==
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* {{Cite book |last=Hunner |first=Jon |title=Inventing Los Alamos |date=2004 |publisher=University of Oklahoma Press |isbn=978-0-8061-3891-6}}
* {{Cite book |last1=Hurst |first1=D. G. |url=http://www.scintillators.ru/booc/criticality/reports/ref_066.pdf |title=Canadian Research Reactors |last2=Ward |first2=A. G. |date=1956 |publisher=Atomic Energy of Canada Limited |location=Ottawa |oclc=719819357 |access-date=February 6, 2015 |archive-url=https://web.archive.org/web/20150205221008/http://www.scintillators.ru/booc/criticality/reports/ref_066.pdf |archive-date=February 5, 2015 |url-status=live}}
* <!-- J -->{{Cite book |last=Jha |first=D. K. |url=https://books.google.com/books?id=L79odes2ihEC&pg=PA73 |title=Nuclear Energy |date=2004 |publisher=Discovery Publishing House |isbn=81-7141-884-8 |access-date=January 6, 2022 |archive-url=https://web.archive.org/web/20220106154121/https://books.google.com/books?id=L79odes2ihEC&pg=PA73 |archive-date=January 6, 2022 |url-status=live}}
* <!-- K -->{{Cite book |last1=Kaku |first1=Michio |url=https://books.google.com/books?id=7A9A9BSk0eUC&q=ralph%20nader%20microgram%20plutonium&pg=PA77 |title=Nuclear Power, Both Sides: The Best Arguments for and Against the Most Controversial Technology |last2=Trainer |first2=Jennifer |date=1983 |publisher=W. W. Norton & Company |isbn=9780393301281 |access-date=December 8, 2013 |archive-url=https://web.archive.org/web/20220106154030/https://books.google.com/books?id=7A9A9BSk0eUC&pg=PA77&q=ralph%20nader%20microgram%20plutonium |archive-date=January 6, 2022 |url-status=live}}
* {{Cite book |last=Kay |first=A. E. |url=https://books.google.com/books?id=8r8NAAAAQAAJ&pg=PA456 |title=plutonium 1965 |date=1965 |publisher=Taylor & Francis |access-date=January 6, 2022 |archive-url=https://web.archive.org/web/20220106154123/https://books.google.com/books?id=8r8NAAAAQAAJ&pg=PA456 |archive-date=January 6, 2022 |url-status=live}}
* <!-- Li -->{{Cite book |title=Handbook of Chemistry and Physics |date=2006 |publisher=CRC Press, Taylor & Francis Group |isbn=0-8493-0487-3 |editor-last=Lide |editor-first=David R. |edition=87th |location=Boca Raton}}
* <!-- Ma -->{{Cite book |url=https://www-nds.iaea.org/publications/indc/indc_usa_0085_II.pdf |title=Proceedings of the conference on nuclear data evaluation methods and procedures. BNL-NCS 51363. |date=1981 |publisher=[[Brookhaven National Laboratory]] |editor-last=Magurno |editor-first=B. A. |volume=II |location=Upton |access-date=August 6, 2014 |editor-last2=Pearlstein |editor-first2=S. |archive-url=https://web.archive.org/web/20210308125416/https://www-nds.iaea.org/publications/indc/indc_usa_0085_II.pdf |archive-date=March 8, 2021 |url-status=live}}
* {{Cite book |last=Martin |first=James E. |title=Physics for Radiation Protection |date=2000 |publisher=Wiley-Interscience |isbn=0-471-35373-6}}
* <!-- Mc -->{{Cite book |last1=McLaughlin |first1=Thomas P. |url=http://library.lanl.gov/cgi-bin/getfile?00314607.pdf |title=A Review of Criticality Accidents |last2=Monahan |first2=Shean P. |last3=Pruvost |first3=Norman L. |date=2000 |publisher=Los Alamos National Laboratory |location=Los Alamos |id=LA-13638 |access-date=February 6, 2015 |archive-url=https://web.archive.org/web/20170118111722/http://library.lanl.gov/cgi-bin/getfile?00314607.pdf |archive-date=January 18, 2017 |url-status=live}}
* <!-- Mi -->{{Cite book |last1=Miner |first1=William N. |title=The Encyclopedia of the Chemical Elements |last2=Schonfeld, Fred W. |publisher=Reinhold Book Corporation |year=1968 |editor-last=Clifford A. Hampel |location=New York (NY) |pages=[https://archive.org/details/encyclopediaofch00hamp/page/540 540–546] |chapter=Plutonium |lccn=68029938 |ref=CITEREFMiner1968 |chapter-url=https://archive.org/details/encyclopediaofch00hamp |chapter-url-access=registration}}
* <!-- Mo -->{{Cite book |last1=Moody |first1=Kenton James |url=https://books.google.com/books?id=W3FnEOg8tS4C&pg=PA169 |title=Nuclear forensic analysis |last2=Hutcheon |first2=Ian D. |last3=Grant |first3=Patrick M. |date=2005 |publisher=CRC Press |isbn=0-8493-1513-1 |access-date=January 6, 2022 |archive-url=https://web.archive.org/web/20220106154123/https://books.google.com/books?id=W3FnEOg8tS4C&pg=PA169 |archive-date=January 6, 2022 |url-status=live}}
* <!-- Rh -->{{Cite book |last=Rhodes |first=Richard |title=The Making of the Atomic Bomb |title-link=The Making of the Atomic Bomb |date=1986 |publisher=Simon & Schuster |isbn=0-671-65719-4 |location=New York |author-link=Richard Rhodes}}
* <!-- Se -->{{Cite book |last1=Seaborg |first1=G. T. |url=https://archive.org/details/adventuresinatom00seab |title=Adventures in the Atomic Age: From Watts to Washington |last2=Seaborg |first2=E. |date=2001 |publisher=Farrar, Straus and Giroux |isbn=0-374-29991-9 |url-access=registration}}
* <!-- Sk -->{{Cite book |last=Sklar |first=Morty |title=Nuke-Rebuke: Writers & Artists Against Nuclear Energy & Weapons |date=1984 |publisher=The Spirit That Moves Us Press |series=The Contemporary anthology series}}
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{{refend}}

==External links==
{{Spoken Wikipedia|Plutonium.ogg|date=2009-07-18}}
* {{Cite web |title=Alsos Digital Library for Nuclear Issues – Plutonium |url=http://alsos.wlu.edu/qsearch.aspx?browse=science/Plutonium |url-status=dead |archive-url=https://web.archive.org/web/20090203184521/http://alsos.wlu.edu/qsearch.aspx?browse=science%2FPlutonium |archive-date=February 3, 2009 |access-date=February 15, 2009 |publisher=[[Washington and Lee University]]}}
* {{Cite web |last=Sutcliffe |first=W. G. |display-authors=etal |date=1995 |title=A Perspective on the Dangers of Plutonium |url=http://www.llnl.gov/csts/publications/sutcliffe/ |archive-url=https://web.archive.org/web/20060929015050/http://www.llnl.gov/csts/publications/sutcliffe/ |archive-date=September 29, 2006 |publisher=[[Lawrence Livermore National Laboratory]]}}
* {{Cite web |date=2005 |title=Physical, Nuclear, and Chemical, Properties of Plutonium |url=http://www.ieer.org/fctsheet/pu-props.html |access-date=February 15, 2009 |publisher=[[IEER]]}}
* {{Cite web |title=A History of Plutonium |url=https://discover.lanl.gov/publications/actinide-research-quarterly/first-quarter-2022/shining-light-on-a-dark-element/ |access-date=8 July 2023 |publisher=Los Alamos National Laboratory |language=en}}
* {{Cite web |last=Bhadeshia |first=H. |title=Plutonium crystallography |url=http://www.msm.cam.ac.uk/phase-trans/2006/Plutonium/Plutonium.html}}
* {{Cite journal |last=Samuels |first=D. |date=2005 |title=End of the Plutonium Age |url=http://discovermagazine.com/2005/nov/end-of-plutonium |journal=Discover Magazine |volume=26 |issue=11}}
* {{Cite web |last1=Pike |first1=J. |last2=Sherman, R. |date=2000 |title=Plutonium production |url=https://fas.org/nuke/intro/nuke/plutonium.htm |url-status=dead |archive-url=https://web.archive.org/web/20090203203853/http://www.fas.org/nuke/intro/nuke/plutonium.htm |archive-date=February 3, 2009 |access-date=February 15, 2009 |publisher=[[Federation of American Scientists]]}}
* {{Cite web |title=Plutonium Manufacture and Fabrication |url=http://nuclearweaponarchive.org/Library/Plutonium/}}
* {{Cite web |last=Ong |first=C. |date=1999 |title=World Plutonium Inventories |url=http://www.nuclearfiles.org/menu/key-issues/nuclear-energy/issues/world-plutonium-inventories-ong.htm |archive-url=https://web.archive.org/web/20140805165417/http://www.nuclearfiles.org/menu/key-issues/nuclear-energy/issues/world-plutonium-inventories-ong.htm |archive-date=August 5, 2014 |access-date=February 15, 2009 |publisher=Nuclear Files.org}}
* {{Cite journal |date=2000 |title=Challenges in Plutonium Science |url=https://fas.org/sgp/othergov/doe/lanl/pubs/number26.htm |journal=Los Alamos Science |volume=I & II |issue=26 |access-date=February 15, 2009}}
* {{Cite web |title=Plutonium |url=http://www.rsc.org/images/CIIE_plutonium_48kbps_tcm18-121120.MP3 |access-date=February 6, 2015 |publisher=[[Royal Society of Chemistry]]}}
* {{Cite web |title=Plutonium |url=http://www.periodicvideos.com/videos/094.htm |access-date=February 6, 2015 |series=[[The Periodic Table of Videos]] |publisher=University of Nottingham}}
* {{YouTube|aI8VyCZlkwA|''Plutonium Fuel Fabrication'' by Argonne National Laboratory}}

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[[Category:Plutonium| ]]
[[Category:Chemical elements]]
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