View source for Plutonium-239

{{Short description|Isotope of plutonium}}
{{About|an isotope of plutonium|the film|Pu-239 (film){{!}}''Pu-239'' (film)}}
{{Infobox isotope
 | alternate_names =
 | symbol =Pu
 | mass_number =239
 | mass = 239.0521634
 | num_neutrons =145
 | num_protons =94
 | abundance =
 | halflife = {{val|24110|u=years}}
 | image = Plutonium-239, 1941, first sample in which nuclear fission was detected, University of California, Berkeley, gift of Glenn T. Seabort and Emilio Segre - National Museum of American History - DSC06250.JPG
 | image_caption = The first sample of plutonium in which nuclear fission was detected, pictured above, was a sample of plutonium-239.
 | decay_product =Uranium-235
 | decay_symbol =U
 | decay_mass =235
 | decay_mode1 =[[Alpha decay]]
 | decay_energy1 = 5.156
 | decay_mode2 =
 | decay_energy2 =
 | decay_mode3 =
 | decay_energy3 =
 | decay_mode4 =
 | decay_energy4 =
 | parent = Curium-243
 | parent_symbol =Cm
 | parent_mass =243
 | parent_decay =a
 | parent2 =Americium-239
 | parent2_symbol =Am
 | parent2_mass =239
 | parent2_decay =ec
 | parent3 =Neptunium-239
 | parent3_symbol =Np
 | parent3_mass =239
 | parent3_decay =b
 | spin = +{{frac|1|2}}
 | excess_energy =
 | binding_energy =
}}

'''Plutonium-239''' ('''{{SimpleNuclide|Plutonium|239}}''' or '''Pu-239''') is an [[isotope of plutonium]]. Plutonium-239 is the primary [[fissile]] isotope used for the production of [[nuclear weapon]]s, although [[uranium-235]] is also  used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum [[nuclear reactor]]s, along with [[uranium-235]] and [[uranium-233]]. Plutonium-239 has a [[half-life]] of 24,110 years.<ref>{{cite web|url=http://ieer.org/resource/nuclear-power/plutonium-factsheet/|title=Physical, Nuclear, and Chemical Properties of Plutonium|work=Institute for Energy and Environmental Research|access-date=20 November 2015}}</ref>

== Nuclear properties ==
The nuclear properties of plutonium-239, as well as the ability to produce large amounts of nearly pure <sup>239</sup>Pu more cheaply than highly enriched [[weapons-grade]] uranium-235, led to its use in nuclear weapons and nuclear power plants. The [[nuclear fission|fissioning]] of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be [[Neutron capture|absorbed]] by uranium-238 to produce plutonium-239 and other isotopes. Plutonium-239 can also absorb neutrons and fission along with the uranium-235 in a reactor.

Of all the common nuclear fuels, <sup>239</sup>Pu has the smallest [[critical mass]]. A spherical untamped critical mass is about 11&nbsp;kg (24.2&nbsp;lbs),<ref>[https://fas.org/nuke/intro/nuke/design.htm FAS Nuclear Weapons Design FAQ] {{webarchive |url=https://web.archive.org/web/20081226091803/http://www.fas.org/nuke/intro/nuke/design.htm |date=December 26, 2008}}, Accessed 2010-9-2</ref> 10.2&nbsp;cm (4") in diameter. Using appropriate triggers, neutron reflectors, implosion geometry and [[Tamper (nuclear weapon)|tampers]], the critical mass can be less than half of that.

The fission of one atom of <sup>239</sup>Pu generates 207.1 [[electronvolt|MeV]] = 3.318 × 10<sup>−11</sup> J, i.e. 19.98 TJ/[[mole (unit)|mol]] = 83.61 TJ/kg,<ref name="kayelaby">{{cite web |url=http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html |title=Table of Physical and Chemical Constants, Sec 4.7.1: Nuclear Fission |publisher=Kaye & Laby Online |access-date=2009-02-01 |archive-url=https://web.archive.org/web/20100305114800/http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html |archive-date=2010-03-05 |url-status=dead }}</ref> or about 23 gigawatt hours/kg.

{| class="wikitable"  style="margin:1em auto;" align="center"
|-
!radiation source (thermal fission of <sup>239</sup>Pu)  !!average energy released [MeV]<ref name="kayelaby" />
|-
|Kinetic energy of fission fragments || style="background:#e0ffe0; text-align:center" | 175.8
|-
|Kinetic energy of prompt neutrons || style="background:#e0ffe0; text-align:center" | &nbsp; &nbsp; 5.9
|-
|Energy carried by prompt γ-rays || style="background:#e0ffe0; text-align:center" | &nbsp; &nbsp; 7.8
|-
|style="background:#8989f9" | Total instantaneous energy || style="background:#8989f9; text-align:center" | 189.5
|-
|Energy of β− particles || style="background:#e0ffe0; text-align:center" | &nbsp; &nbsp; 5.3
|-
|Energy of antineutrinos || style="text-align:center" | &nbsp; &nbsp; 7.1
|-
|Energy of delayed γ-rays || style="background:#e0ffe0; text-align:center" | &nbsp; &nbsp; 5.2
|-
|style="background:#8989f9" | Total from decaying fission products || style="background:#8989f9; text-align:center" | &nbsp; 17.6
|-
|Energy released by radiative capture of prompt neutrons || style="background:#e0ffe0; text-align:center" | &nbsp; 11.5
|-
|style="background:#60c060" | Total heat released in a thermal-spectrum reactor (anti-neutrinos do not contribute) || style="background:#60c060; text-align:center" | 211.5
|}

== Production ==
{{More citations needed section|find=plutonium-239|find2=supergrade, rbmk, phwr, ifr, nuclear weapons|date=July 2024}}
Plutonium is made from [[uranium-238]]. <sup>239</sup>Pu is normally created in nuclear reactors by [[Nuclear transmutation|transmutation]] of individual atoms of one of the isotopes of uranium present in the fuel rods. Occasionally, when an atom of <sup>238</sup>U is exposed to [[neutron radiation]], its nucleus will capture a [[neutron]], changing it to [[Uranium-239|<sup>239</sup>U]]. This happens more often with lower kinetic energy (as <sup>238</sup>U fission activation is 6.6MeV). The <sup>239</sup>U then rapidly undergoes two [[beta decay|β<sup>−</sup> decays]] — an emission of an [[electron]] and an [[antineutrino|anti-neutrino]] (<math>\bar{\nu}_e</math>), leaving a proton in the nucleus — the first β<sup>−</sup> decay transforming the <sup>239</sup>U into [[neptunium-239]], and the second β<sup>−</sup> decay transforming the <sup>239</sup>Np into <sup>239</sup>Pu:

:<chem>{}^{238}_{92}U + {}^{1}_{0}n -> {}^{239}_{92}U ->[\beta^-][23.5\ \ce{min}] {}^{239}_{93}Np ->[\beta^-][2.356\ \ce{d}] {}^{239}_{94}Pu</chem>

Fission activity is relatively rare, so even after significant exposure, the <sup>239</sup>Pu is still mixed with a great deal of <sup>238</sup>U (and possibly other isotopes of uranium), oxygen, other components of the original material, and [[fission products]]. Only if the fuel has been exposed for a few days in the reactor, can the <sup>239</sup>Pu be [[nuclear reprocessing|chemically separated]] from the rest of the material to yield high-purity <sup>239</sup>Pu metal.

<sup>239</sup>Pu has a higher probability for fission than <sup>235</sup>U and a larger number of neutrons produced per fission event, so it has a smaller critical mass. Pure <sup>239</sup>Pu also has a reasonably low rate of neutron emission due to [[spontaneous fission]] (10 fission/s·kg), making it feasible to assemble a mass that is highly supercritical before a detonation [[nuclear chain reaction|chain reaction]] begins.

In practice, however, reactor-bred plutonium will invariably contain a certain amount of [[plutonium-240|<sup>240</sup>Pu]] due to the tendency of <sup>239</sup>Pu to absorb an additional neutron during production. <sup>240</sup>Pu has a high rate of spontaneous fission events (415,000 fission/s-kg), making it an undesirable contaminant. As a result, plutonium containing a significant fraction of <sup>240</sup>Pu is not well-suited to use in nuclear weapons; it emits neutron radiation, making handling more difficult, and its presence can lead to a "[[Fizzle (nuclear test)|fizzle]]" in which a small explosion occurs, destroying the weapon but not causing fission of a significant fraction of the fuel. It is because of this limitation that plutonium-based weapons must be implosion-type, rather than gun-type. Moreover, <sup>239</sup>Pu and <sup>240</sup>Pu cannot be chemically distinguished, so expensive and difficult [[isotope separation]] would be necessary to separate them. Weapons-grade plutonium is defined as containing no more than 7% <sup>240</sup>Pu; this is achieved by only exposing <sup>238</sup>U to neutron sources for short periods of time to minimize the <sup>240</sup>Pu produced.

Plutonium is classified according to the percentage of the contaminant plutonium-240 that it contains:

* '''Supergrade''' 2–3%
* '''Weapons grade''' 3–7%
* '''Fuel grade''' 7–18%
* '''[[Reactor grade plutonium|Reactor grade]]''' 18% or more

A nuclear reactor that is used to produce plutonium for weapons therefore generally has a means for exposing <sup>238</sup>U to neutron radiation and for frequently replacing the irradiated <sup>238</sup>U with new <sup>238</sup>U. A reactor running on unenriched or moderately enriched uranium contains a great deal of <sup>238</sup>U. However, most commercial nuclear power reactor designs require the entire reactor to shut down, often for weeks, in order to change the fuel elements. They therefore produce plutonium in a mix of isotopes that is not well-suited to weapon construction.  Such a reactor could have machinery added that would permit <sup>238</sup>U slugs to be placed near the core and changed frequently, or it could be shut down frequently, so proliferation is a concern; for this reason, the [[International Atomic Energy Agency]] inspects licensed reactors often. A few commercial power reactor designs, such as the ''reaktor bolshoy moshchnosti kanalniy'' ([[RBMK]]) and pressurized heavy water reactor ([[PHWR]]), do permit refueling without shutdowns, and they may pose a proliferation risk.  By contrast, the Canadian [[CANDU]] heavy-water moderated, natural-uranium fueled reactor can also be refueled while operating, but it normally consumes most of the <sup>239</sup>Pu it produces ''in situ;''  thus, it is not only inherently less proliferative than most reactors, but can even be operated as an "[[Nuclear transmutation#Artificial transmutation of nuclear waste|actinide incinerator]]".<ref>{{cite web |url=http://www.nuclearfaq.ca/brat_fuel.htm |date=April 14, 2000 |title=The Evolution of CANDU Fuel Cycles and their Potential Contribution to World Peace |first=Jeremy J.|last=Whitlock}}</ref> The American [[Integral Fast Reactor|IFR]] (Integral Fast Reactor) can also be operated in an incineration mode, having some advantages in not accumulating the [[plutonium-242]] isotope or the long-lived [[actinide]]s, which cannot be easily burned except in a fast reactor. Also IFR fuel has a high proportion of burnable isotopes, while in CANDU an inert material is needed to dilute the fuel; this means the IFR can burn a higher fraction of its fuel before needing reprocessing. Most plutonium is produced in [[research reactor]]s or plutonium production reactors called [[breeder reactor]]s because they produce more plutonium than they consume fuel; in principle, such reactors make extremely efficient use of natural uranium.  In practice, their construction and operation is sufficiently difficult that they are generally only used to produce plutonium. Breeder reactors are generally (but not always) [[fast reactor]]s, since [[fast neutron]]s are somewhat more efficient at plutonium production.

Plutonium-239 is more frequently used in nuclear weapons than uranium-235, as it is easier to obtain in a quantity of critical mass. Both plutonium-239 and uranium-235 are obtained from [[Natural uranium]], which primarily consists of uranium-238 but contains traces of other isotopes of uranium such as uranium-235. The process of [[Uranium enrichment|enriching uranium]], i.e. increasing the ratio of <sup>235</sup>U to <sup>238</sup>U to weapons grade, is generally a more lengthy and costly process than the production of plutonium-239 from <sup>238</sup>U and subsequent reprocessing.

=== Supergrade plutonium ===
{{Unreferenced section|find=supergrade plutonium|date=July 2024}}
The "supergrade" fission fuel, which has less radioactivity, is used in the primary stage of US Navy nuclear weapons in place of the conventional plutonium used in the Air Force's versions. "Supergrade" is industry parlance for plutonium alloy bearing an exceptionally high fraction of <sup>239</sup>Pu (>95%), leaving a very low amount of <sup>240</sup>Pu, which is a high spontaneous fission isotope (see above). Such plutonium is produced from fuel rods that have been irradiated a very short time as measured in MW-day/ton [[burnup]]. Such low irradiation times limit the amount of additional neutron capture and therefore buildup of alternate isotope products such as <sup>240</sup>Pu in the rod, and also by consequence is considerably more expensive to produce, needing far more rods irradiated and processed for a given amount of plutonium.

Plutonium-240, in addition to being a neutron emitter after fission, is a [[gamma radiation|gamma]] emitter, and so is responsible for a large fraction of the radiation from stored nuclear weapons. Whether out on patrol or in port, submarine crew members routinely live and work in very close proximity to nuclear weapons stored in torpedo rooms and missile tubes, unlike Air Force missiles where exposures are relatively brief. The need to reduce radiation exposure justifies the additional costs of the premium supergrade alloy used on many naval nuclear weapons. Supergrade plutonium is used in [[W80 (nuclear warhead)|W80]] warheads. <!-- taken from W80 -->

== In nuclear power reactors ==
In any operating nuclear reactor containing <sup>238</sup>U, some plutonium-239 will accumulate in the nuclear fuel.<ref>{{cite book |title=Radioactivity, Ionizing Radiation, and Nuclear Energy |last1=Hala |first1=Jiri |first2=James D.|last2=Navratil|year=2003 |publisher=Konvoj |location=Brno |isbn=80-7302-053-X |url=https://books.google.com/books?id=3CDjygAACAAJ |page=102}}</ref> Unlike reactors used to produce weapons-grade plutonium, commercial nuclear power reactors typically operate at a high burnup that allows a significant amount of plutonium to build up in irradiated reactor fuel. Plutonium-239 will be present both in the reactor core during operation and in [[spent nuclear fuel]] that has been removed from the reactor at the end of the fuel assembly's service life (typically several years). Spent nuclear fuel commonly contains about 0.8% plutonium-239.

Plutonium-239 present in reactor fuel can absorb neutrons and fission just as uranium-235 can. Since plutonium-239 is constantly being created in the reactor core during operation, the use of plutonium-239 as nuclear fuel in power plants can occur without reprocessing of spent fuel; the plutonium-239 is fissioned in the same fuel rods in which it is produced. Fissioning of plutonium-239 provides more than one-third of the total energy produced in a typical commercial nuclear power plant.<ref>{{cite web|title=Information Paper 15: Plutonium|url=http://www.world-nuclear.org/info/inf15.html|publisher=World Nuclear Association|access-date=15 July 2020|archive-date=30 March 2010|archive-url=https://web.archive.org/web/20100330221426/http://www.world-nuclear.org/info/inf15.html|url-status=dead}}</ref> Reactor fuel would accumulate much more than 0.8% plutonium-239 during its service life if some plutonium-239 were not constantly being "burned off" by fissioning.

A small percentage of plutonium-239 can be deliberately added to fresh nuclear fuel. Such fuel is called [[MOX fuel|MOX (mixed oxide) fuel]], as it contains a mixture of uranium dioxide (UO<sub>2</sub>) and plutonium dioxide (PuO<sub>2</sub>). The addition of plutonium-239 reduces the need to enrich the uranium in the fuel.

== Hazards ==
Plutonium-239 emits [[alpha particles]] to become uranium-235. As an alpha emitter, plutonium-239 is not particularly dangerous as an external radiation source, but if it is ingested or breathed in as dust it is very dangerous and [[carcinogen]]ic. It has been estimated that a pound (454 grams) of plutonium inhaled as plutonium oxide dust could give cancer to two million people.<ref name="tno_chapter13">{{cite book|title=The Nuclear Energy Option|year=1990|publisher=Plenum Press|isbn=978-0-306-43567-6|chapter-url=https://archive.org/details/nuclearenergyopt0000cohe|first=Bernard L.|last=Cohen|author-link=Bernard Cohen (physicist)|chapter=Chapter 13, Plutonium and bombs|chapter-url-access=registration|url-access=registration|url=https://archive.org/details/nuclearenergyopt0000cohe}}</ref> However, ingested plutonium is by far less dangerous as only a tiny fraction is absorbed in gastrointestinal tract;<ref>{{cite book|title=The Nuclear Energy Option|year=1990|publisher=Plenum Press|isbn=978-0-306-43567-6|chapter-url=https://archive.org/details/nuclearenergyopt0000cohe|first=Bernard L.|last=Cohen|author-link=Bernard Cohen (physicist)|chapter=Chapter 11, HAZARDS OF HIGH-LEVEL RADIOACTIVE WASTE — THE GREAT MYTH|chapter-url-access=registration|url-access=registration|url=https://archive.org/details/nuclearenergyopt0000cohe}}</ref><ref name="Emsley2001">{{cite book |title = Nature's Building Blocks: An A–Z Guide to the Elements |last = Emsley |first = John |chapter-url=https://books.google.com/books?id=j-Xu07p3cKwC&pg=PA324 |pages=324–329 |publisher = Oxford University Press |year = 2001 |location = Oxford (UK) |isbn = 0-19-850340-7 |chapter = Plutonium }}</ref> 800&nbsp;mg would be unlikely to cause a major health risk as far as radiation is concerned.<ref name="tno_chapter13" /> As a [[Heavy metal (chemistry)|heavy metal]], plutonium is also chemically toxic. See also [[Plutonium#Precautions|Nuclear Precautions]].

Weapons grade plutonium (with greater than 90% <sup>239</sup>Pu) is used to make nuclear weapons and has many advantages over other fissile material for that purpose. Lower proportions of <sup>239</sup>Pu would make a reliable weapon design difficult or impossible; this is due to the spontaneous fission (and thus neutron production) of the undesirable <sup>240</sup>Pu.

== See also ==
* [[Isotopes of plutonium]]

== References ==
{{Reflist|colwidth=30em}}

== External links ==
* [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+plutonium,+radioactive NLM Hazardous Substances Databank – Plutonium, Radioactive]
* [https://web.archive.org/web/20170922002259/http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_6/4_6_1_part09_090_099.html#Pu Table of nuclides with <sup>239</sup>Pu data at Kaye and Laby Online]
* [http://www.nucleide.org/DDEP_WG/Nuclides/Pu-239_tables.pdf Half-life of Plutonium-239] {{Webarchive|url=https://web.archive.org/web/20110815170004/http://www.nucleide.org/DDEP_WG/Nuclides/Pu-239_tables.pdf |date=2011-08-15 }}

{{Isotope sequence
|element=plutonium
|lighter=[[plutonium-238]]
|heavier=[[plutonium-240]]
|before=[[curium-243]] '''([[alpha decay|α]])'''<br />[[americium-239]] '''([[electron capture|EC]])'''<br />[[neptunium-239]] '''([[beta decay|β<sup>−</sup>]])'''<nowiki/>
|after=[[uranium-235]] '''(α)'''<nowiki/>
}}
{{Isotopes of plutonium}}

[[Category:Actinides]]
[[Category:Fissile materials]]
[[Category:Isotopes of plutonium]]
[[Category:Special nuclear materials]]
[[Category:Radioactive contamination]]