Plutonium Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...

(Pu) is an artificial element, except for trace quantities resulting from

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

, and thus a

standard atomic weight The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, ...

cannot be given. Like all artificial elements, it has no

stable isotope Stable nuclides are Isotope, isotopes of a chemical element whose Nucleon, nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The Atomic nucleus, nuclei of such isotopes are no ...

s. It was synthesized before being found in nature, with the first

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

synthesized being Pu in 1940. Twenty-two plutonium

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s have been characterized. The most stable are Pu with a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 81.3 million years; Pu with a half-life of 373,300 years; Pu with a half-life of 24,110 years; and Pu with a half-life of 6,560 years. This element also has eight

meta state A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state levels (higher energy levels). "Metastable" describes nuclei whose excited states have half-lives of 10−9 s ...

s; all have half-lives of less than one second. The known isotopes of plutonium range from Pu to Pu. The primary

decay mode Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

s before the most stable isotope, Pu, are

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic proc ...

and

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an a ...

; the primary mode after is beta emission. The primary

decay product In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps ( d ...

s before Pu are

isotopes of uranium Uranium (U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. The d ...

and

neptunium Neptunium is a chemical element; it has chemical symbol, symbol Np and atomic number 93. A radioactivity, radioactive actinide metal, neptunium is the first transuranic element. It is named after Neptune, the planet beyond Uranus in the Solar Syste ...

(not considering

fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the releas ...

s), and the primary decay products after are

isotopes of americium Americium (95Am) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no known stable isotopes. The first isotope to be synthesized was 241Am in 1944. The artificial element decays by e ...

List of isotopes

, -id=Plutonium-226 , Pu , style="text-align:right" , 94 , style="text-align:right" , 132 , 226.03825(22)# , ≥1 ms , α , U , 0+ , , -id=Plutonium-227 , Pu , style="text-align:right" , 94 , style="text-align:right" , 133 , 227.03947(11)# , , α , U , 5/2+# , , -id=Plutonium-228 , Pu , style="text-align:right" , 94 , style="text-align:right" , 134 , 228.038763(25) , 2.1(13) s , α , U , 0+ , , -id=Plutonium-229 , rowspan=3, Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 135 , rowspan=3, 229.040145(65) , rowspan=3, 91(26) s , α (~50%) , U , rowspan=3, 3/2+# , rowspan=3, , - , β (~50%) , Np , - , SF (<7%) , (various) , -id=Plutonium-230 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 136 , rowspan=2, 230.039648(16) , rowspan=2, 105(10) s , α (>73%) , U , rowspan=2, 0+ , rowspan=2, , - , β (<27%) , Np , -id=Plutonium-231 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 137 , rowspan=2, 231.041126(24) , rowspan=2, 8.6(5) min , β (87%) , Np , rowspan=2, (3/2+) , rowspan=2, , - , α (13%) , U , -id=Plutonium-232 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 138 , rowspan=2, 232.041182(18) , rowspan=2, 33.7(5) min , EC (77%) , Np , rowspan=2, 0+ , rowspan=2, , - , α (23%) , U , -id=Plutonium-233 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 139 , rowspan=2, 233.042997(58) , rowspan=2, 20.9(4) min , β (99.88%) , Np , rowspan=2, 5/2+# , rowspan=2, , - , α (0.12%) , U , -id=Plutonium-234 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 140 , rowspan=2, 234.0433175(73) , rowspan=2, 8.8(1) h , EC (94%) , Np , rowspan=2, 0+ , rowspan=2, , - , α (6%) , U , -id=Plutonium-235 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 141 , rowspan=2, 235.045285(22) , rowspan=2, 25.3(5) min , β , Np , rowspan=2, (5/2+) , rowspan=2, , - , α (0.0028%) , U , -id=Plutonium-236 , rowspan=3, Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 142 , rowspan=3, 236.0460567(19) , rowspan=3, 2.858(8) y , αTheorized to also undergo β⁺β⁺ decay to ²³⁶U , U , rowspan=3, 0+ , rowspan=3, , - , SF (1.9×10%) , (various) , - , CD (2×10%) , Pb
Mg , -id=Plutonium-236m , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 1185.45(15) keV , 1.2(3) μs , IT , Pu , 5− , , -id=Plutonium-237 , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 143 , rowspan=2, 237.0484079(18) , rowspan=2, 45.64(4) d , EC , Np , rowspan=2, 7/2− , rowspan=2, , - , α (0.0042%) , U , -id=Plutonium-237m1 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 145.543(8) keV , 180(20) ms , IT , Pu , 1/2+ , , -id=Plutonium-237m2 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 2900(250) keV , 1.1(1) μs , SF , (various) , , , - , rowspan=5, Pu , rowspan=5 style="text-align:right" , 94 , rowspan=5 style="text-align:right" , 144 , rowspan=5, 238.0495582(12) , rowspan=5, 87.7(1) y , α , U , rowspan=5, 0+ , rowspan=5, Trace

Double beta decay In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move cl ...

product of U , - , SF (1.9×10%) , (various) , - , CD (1.4×10%) , Hg
Si , - , CD (<6×10%) , Pb
Mg , - , CD (<6×10%) , Pb
Mg , - , rowspan=2, Pufissile nuclideMost useful isotope for nuclear weapons , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 145 , rowspan=2, 239.0521616(12) , rowspan=2, 2.411(3)×10⁴ y , α , ''U'' , rowspan=2, 1/2+ , rowspan=2, Trace

Neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

product of U , - , SF (3.1×10%) , (various) , -id=Plutonium-239m1 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 391.584(3) keV , 193(4) ns , IT , ²³⁹Pu , 7/2− , , -id=Plutonium-239m2 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 3100(200) keV , 7.5(10) μs , SF , (various) , (5/2+) , , - , rowspan=3, Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 146 , rowspan=3, 240.0538117(12) , rowspan=3, 6.561(7)×10 y , α , U , rowspan=3, 0+ , rowspan=3, TraceIntermediate decay product of Pu , - , SF (5.796×10%) , (various) , - , CD (<1.3×10%) , Hg
Si , -id=Plutonium-240m , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 1308.74(5) keV , 165(10) ns , IT , ²⁴⁰Pu , 5− , , - , rowspan=3, Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 147 , rowspan=3, 241.0568497(12) , rowspan=3, 14.329(29) y , β , Am , rowspan=3, 5/2+ , rowspan=3, , - , α (0.00245%) , U , - , SF (<2.4×10%) , (various) , -id=Plutonium-241m1 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 161.6853(9) keV , 0.88(5) μs , IT , ²⁴¹Pu , 1/2+ , , -id=Plutonium-241m2 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 2200(200) keV , 20.5(22) μs , SF , (various) , , , - , rowspan=2, Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 242.0587410(13) , rowspan=2, 3.75(2)×10 y , α , ''U'' , rowspan=2, 0+ , rowspan=2, , - , SF (5.510×10%) , (various) , -id=Plutonium-243 , Pu , style="text-align:right" , 94 , style="text-align:right" , 149 , 243.0620021(27) , 4.9553(25) h , β , Am , 7/2+ , , -id=Plutonium-243m , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 383.64(25) keV , 330(30) ns , IT , ²⁴³Pu , (1/2+) , , - , rowspan=3, Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 150 , rowspan=3, 244.0642044(25) , rowspan=3, 8.13(3)×10 y , α (99.88%) , U , rowspan=3, 0+ , rowspan=3, TraceInterstellar, some may also be primordial but such claims are disputed , - , SF (0.123%) , (various) , - , ββ (<7.3×10%) , Cm , -id=Plutonium-244m , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 1216.0(5) keV , 1.75(12) s , IT , ²⁴⁴Pu , 8− , , -id=Plutonium-245 , Pu , style="text-align:right" , 94 , style="text-align:right" , 151 , 245.067825(15) , 10.5(1) h , β , Am , (9/2−) , , -id=Plutonium-245m1 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 264.5(3) keV , 330(20) ns , IT , ²⁴⁵Pu , (5/2+) , , -id=Plutonium-245m2 , style="text-indent:1em" , Pu , colspan="3" style="text-indent:2em" , 2000(400) keV , 90(30) ns , SF , (various) , , , -id=Plutonium-246 , Pu , style="text-align:right" , 94 , style="text-align:right" , 152 , 246.070204(16) , 10.84(2) d , β , Am , 0+ , , -id=Plutonium-247 , Pu , style="text-align:right" , 94 , style="text-align:right" , 153 , 247.07430(22)# , 2.27(23) d , β , Am , 1/2+# ,

Actinides vs fission products

Notable isotopes

Plutonium-238 Plutonium-238 ( or Pu-238) is a radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter; as alpha particles are easily blocked, this makes the plutonium-238 isotope suitable for usage ...

has a half-life of 87.74 years and emits

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...

s. Pure Pu for

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the Decay heat, heat released by the decay of a suitable radioactive material i ...

s that power some

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

is produced by neutron capture on

neptunium-237 Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be ...

but plutonium from

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...

can contain as much as a few percent Pu, originating from Np,

of Cm, or (n,2n) reactions. *

Plutonium-239 Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...

has half-life 24,100 years. Pu and Pu are

fissile In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal Nuclear chain reaction#Fission chain reaction, chain reaction can only be achieved with fissil ...

; meaning their nuclei can

split Split(s) or The Split may refer to: Places * Split, Croatia, the largest coastal city in Croatia * Split Island, Canada, an island in the Hudson Bay * Split Island, Falkland Islands * Split Island, Fiji, better known as Hạfliua Arts, enter ...

by being bombarded by slow thermal neutrons, releasing energy,

gamma radiation A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

and more neutrons. It can therefore sustain a

nuclear chain reaction In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series or "positive feedback loop" of thes ...

, leading to applications in

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

s and

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

s. Pu is synthesized by irradiating

uranium-238 Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...

with neutrons in a nuclear reactor, then recovered via

nuclear reprocessing Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...

of the fuel. Further

produces successively heavier isotopes. *

Plutonium-240 Plutonium-240 ( or Pu-240) is an isotope of plutonium formed when plutonium-239 captures a neutron. The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project. ...

has a high rate of spontaneous fission, raising the background

neutron radiation Neutron radiation is a form of ionizing radiation that presents as free neutrons. Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new nuclides— ...

of plutonium. Plutonium is graded by proportion of Pu: weapons grade (<7%), fuel grade (7–19%) and reactor grade (>19%). Lower grades are less suited for bombs and

thermal reactor A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and stru ...

s but can fuel

fast reactor A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV, on average), as opposed to slow t ...

s. *

Plutonium-241 Plutonium-241 ( or Pu-241) is an isotope of plutonium formed when plutonium-240 captures a neutron. Like some other plutonium isotopes (especially 239Pu), 241Pu is fissile, with a neutron absorption cross section about one-third greater than t ...

is fissile, but

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

s with a half-life of 14 years to

americium-241 Americium-241 (Am, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of . Am is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It ...

. * Plutonium-242 is not fissile, nor very fertile (requiring 3 more neutron captures to become fissile); and has a low neutron capture cross section, and a longer half-life than any of the lighter isotopes. *

Plutonium-244 Plutonium-244 (Pu) is an isotope of plutonium that has a half-life of 81.3 million years. This is longer than any other isotope of plutonium and longer than any other known isotope of an element beyond bismuth, except for the three naturally abu ...

is the most stable isotope of plutonium, with a half-life of about 80 million years. It is not significantly produced in nuclear reactors because Pu has a short half-life, but some is produced in nuclear explosions. Pu has been found in interstellar space and has the second longest half-life of any non-primordial radioisotope.

Production and uses

Pu, a fissile isotope that is the second most used

nuclear fuel Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other atomic nucleus, nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is ...

in nuclear reactors after

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

, and the most used fuel in the fission portion of

s, is produced from

by neutron capture followed by two beta decays. Pu, Pu, and Pu are produced by further neutron capture. The odd-mass isotopes Pu and Pu have about a 3/4 chance of undergoing fission on capture of a

thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wit ...

and about a 1/4 chance of retaining the

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

and becoming the next heavier isotope. The even-mass isotopes are fertile but not fissile and also have a lower probability ( cross section) of neutron capture; therefore, they tend to accumulate in nuclear fuel used in a thermal reactor, the design of nearly all

nuclear power plant A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...

s today. In plutonium that has been used a second time in thermal reactors in

MOX fuel Mixed oxide fuel (MOX fuel) is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enr ...

, Pu may even be the most common isotope. All plutonium isotopes and other

actinide The actinide () or actinoid () series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. Number 103, lawrencium, is also generally included despite being part ...

s, however, are fissionable with fast neutrons. Pu does have a moderate thermal neutron absorption cross section, so that Pu production in a thermal reactor becomes a significant fraction as large as Pu production. Pu has a half-life of 14 years, and has slightly higher thermal neutron cross sections than Pu for both fission and absorption. While nuclear fuel is being used in a reactor, a Pu nucleus is much more likely to fission or to capture a neutron than to decay. Pu accounts for a significant portion of fissions in thermal reactor fuel that has been used for some time. However, in

that does not quickly undergo nuclear reprocessing but instead is cooled for years after use, much or most of the Pu will beta decay to

, one of the

minor actinide Minor may refer to: Common meanings * Minor (law), a person not under the age of certain legal activities. * Academic minor, a secondary field of study in undergraduate education Mathematics * Minor (graph theory), a relation of one graph to ...

s, a strong alpha emitter, and difficult to use in thermal reactors. Pu has a particularly low cross section for thermal neutron capture; and it takes three neutron absorptions to become another fissile isotope (either curium-245 or Pu) and fission. Even then, there is a chance either of those two fissile isotopes will fail to fission but instead absorb a fourth neutron, becoming curium-246 (on the way to even heavier actinides like

californium Californium is a synthetic chemical element; it has symbol Cf and atomic number 98. It was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory) by bombarding curium with al ...

, which is a neutron emitter by spontaneous fission and difficult to handle) or becoming Pu again; so the mean number of neutrons absorbed before fission is even higher than 3. Therefore, Pu is particularly unsuited to recycling in a thermal reactor and would be better used in a

where it can be fissioned directly. However, Pu's low cross section means that relatively little of it will be transmuted during one cycle in a thermal reactor. Pu's half-life is about 15 times as long as Pu's half-life; therefore, it is 1/15 as radioactive and not one of the larger contributors to

nuclear waste Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...

radioactivity. Pu's

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

emissions are also weaker than those of the other isotopes. Pu has a half-life of only 5 hours, beta decaying to americium-243. Because Pu has little opportunity to capture an additional neutron before decay, the

nuclear fuel cycle The nuclear fuel cycle, also known as the nuclear fuel chain, describes the series of stages that nuclear fuel undergoes during its production, use, and recycling or disposal. It consists of steps in the ''front end'', which are the preparation o ...

does not produce the long-lived Pu in significant quantity. Pu is not normally produced in as large quantity by the nuclear fuel cycle, but some is produced from

by neutron capture (this reaction can also be used with purified neptunium to produce Pu relatively free of other plutonium isotopes for use in

s), by the (n,2n) reaction of fast neutrons on Pu, or by alpha decay of curium-242, which is produced by neutron capture of Am. It has significant thermal neutron cross section for fission, but is more likely to capture a neutron and become Pu.

Manufacture

Plutonium-240, -241 and -242

The fission cross section for Pu is 747.9 barns for thermal neutrons, while the activation cross section is 270.7 barns (the ratio approximates to 11 fissions for every 4 neutron captures). The higher plutonium isotopes are created when the uranium fuel is used for a long time. For high burnup used fuel, the concentrations of the higher plutonium isotopes will be higher than the low burnup fuel that is reprocessed to obtain weapons grade plutonium.

Plutonium-239

Pu is one of the three fissile materials used for the production of nuclear weapons and in some nuclear reactors as a source of energy. The other fissile materials are

and

uranium-233 Uranium-233 ( or U-233) is a fissile isotope of uranium that is bred from thorium-232 as part of the thorium fuel cycle. Uranium-233 was investigated for use in nuclear weapons and as a Nuclear fuel, reactor fuel. It has been used successfully ...

. Pu is virtually nonexistent in nature. It is made by bombarding

with neutrons. Uranium-238 is present in quantity in most reactor fuel; hence Pu is continuously made in these reactors. Since Pu can itself be split by neutrons to release energy, Pu provides a portion of the energy generation in a nuclear reactor.

Plutonium-238

There are small amounts of Pu in the plutonium from usual reactors. However, isotopic separation would be quite expensive compared to another method: when U captures a neutron, it is converted to an excited state of U. Some of the excited U nuclei undergo fission, but some decay to the ground state of U by emitting gamma radiation. Further neutron capture creates U; which, with a half-life of 7 days, decays to Np. Since nearly all neptunium is produced in this way or consists of isotopes that decay quickly, one gets nearly pure Np. After chemical separation of neptunium, Np is again irradiated by reactor neutrons to be converted to Np, which decays to Pu with a half-life of 2 days.

Plutonium-240 as an obstacle to nuclear weapons

Pu undergoes

at a small but significant rate (%). The presence of Pu limits the plutonium's use in a

nuclear bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

, because a neutron from spontaneous fission starts the

chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Chain reactions are one way that sys ...

prematurely, causing an early release of energy that disperses the core before full implosion is reached. This prevents most of the core from participation in the chain reaction and reduces the bomb's yield. Plutonium consisting of more than about 90% Pu is called weapons-grade plutonium; plutonium from

from commercial power reactors generally contains at least 20% Pu and is called reactor-grade plutonium. However, modern nuclear weapons use

fusion boosting A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of Nuclear fusion, fusion fuel to increase the rate, and thus yield, of a Nuclear fission, fission reaction. The Fusion neutron, fast fusion neutrons rele ...

, which mitigates the predetonation problem; if the pit can generate a

nuclear weapon yield The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated. It is usually expressed as a ''TNT equivalent'', the standardized equivalen ...

of even a fraction of a

kiloton TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. A ton of TNT equivalent is a unit of energy defined by convention to be (). It is the approximate energy released in the det ...

, which is enough to start deuterium–tritium fusion, the resulting burst of neutrons will fission enough plutonium to ensure a yield of tens of kilotons. Contamination due to Pu is the reason plutonium weapons must use the implosion method. Theoretically, pure Pu could be used in a gun-type bomb, but achieving this level of purity is prohibitively difficult. Pu contamination has proven a mixed blessing. While it created delays and headaches during the

Manhattan Project The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the ...

because of the need to develop implosion technology, those same difficulties are a barrier to

nuclear proliferation Nuclear proliferation is the spread of nuclear weapons to additional countries, particularly those not recognized as List of states with nuclear weapons, nuclear-weapon states by the Treaty on the Non-Proliferation of Nuclear Weapons, commonl ...

. Implosion bombs are also inherently more efficient and less prone to accidental detonation than are gun-type bombs.

Notes

References

* Isotope masses from: ** * Half-life, spin, and isomer data selected from the following sources. ** ** **

Sources

* * {{Authority control Plutonium