Plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...

(₉₄Pu) is an

artificial element A synthetic element is one of 24 known chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; ...

, 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, ...

by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no

stable isotope The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...

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

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

synthesized being ²³⁸Pu in 1940. Twenty plutonium

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

s have been characterized. The most stable are

plutonium-244 Plutonium-244 (244Pu) is an isotope of plutonium that has a half-life of 80 million years. This is longer than any of the other isotopes of plutonium and longer than any other actinide isotope except for the three naturally abundant ones: uranium ...

with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

of 80.8 million years,

plutonium-242 Plutonium-242 (242Pu or Pu-242) is one of the isotopes of plutonium, the second longest-lived, with a half-life of 375,000 years. The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the la ...

with a half-life of 373,300 years, and

plutonium-239 Plutonium-239 (239Pu 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 ...

with a half-life of 24,110 years. All of the remaining

radioactive 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 consid ...

isotopes have half-lives that are less than 7,000 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 higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited states have ha ...

s; all have half-lives of less than one second. The isotopes of plutonium range in

atomic weight Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...

from 228.0387 u (²²⁸Pu) to 247.074 u (²⁴⁷Pu). 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 consid ...

s before the most stable isotope, ²⁴⁴Pu, are

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdo ...

and

alpha emission Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an at ...

; the primary mode after is

beta emission In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For exam ...

. 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 ( ...

s before ²⁴⁴Pu are

isotopes of uranium Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay ...

and

neptunium Neptunium is a chemical element with the Symbol (chemistry), symbol Np and atomic number 93. A radioactivity, radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after ...

(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 release ...

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 b ...

List of isotopes

, - , rowspan=2, ²²⁸Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 134 , rowspan=2, 228.03874(3) , rowspan=2, 1.1(+20−5) s , α (99.9%) , ²²⁴U , rowspan=2, 0+ , rowspan=2, , - , β⁺ (.1%) , ²²⁸Np , - , ²²⁹Pu , style="text-align:right" , 94 , style="text-align:right" , 135 , 229.04015(6) , 120(50) s , α , ²²⁵U , 3/2+# , , - , rowspan=2, ²³⁰Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 136 , rowspan=2, 230.039650(16) , rowspan=2, 1.70(17) min , α , ²²⁶U , rowspan=2, 0+ , rowspan=2, , - , β⁺ (rare) , ²³⁰Np , - , rowspan=2, ²³¹Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 137 , rowspan=2, 231.041101(28) , rowspan=2, 8.6(5) min , β⁺ , ²³¹Np , rowspan=2, 3/2+# , rowspan=2, , - , α (rare) , ²²⁷U , - , rowspan=2, ²³²Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 138 , rowspan=2, 232.041187(19) , rowspan=2, 33.7(5) min , EC (89%) , ²³²Np , rowspan=2, 0+ , rowspan=2, , - , α (11%) , ²²⁸U , - , rowspan=2, ²³³Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 139 , rowspan=2, 233.04300(5) , rowspan=2, 20.9(4) min , β⁺ (99.88%) , ²³³Np , rowspan=2, 5/2+# , rowspan=2, , - , α (.12%) , ²²⁹U , - , rowspan=2, ²³⁴Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 140 , rowspan=2, 234.043317(7) , rowspan=2, 8.8(1) h , EC (94%) , ²³⁴Np , rowspan=2, 0+ , rowspan=2, , - , α (6%) , ²³⁰U , - , rowspan=2, ²³⁵Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 141 , rowspan=2, 235.045286(22) , rowspan=2, 25.3(5) min , β⁺ (99.99%) , ²³⁵Np , rowspan=2, (5/2+) , rowspan=2, , - , α (.0027%) , ²³¹U , - , rowspan=4, ²³⁶Pu , rowspan=4 style="text-align:right" , 94 , rowspan=4 style="text-align:right" , 142 , rowspan=4, 236.0460580(24) , rowspan=4, 2.858(8) y , α , ²³²U , rowspan=4, 0+ , rowspan=4, , - , SF (1.37×10⁻⁷%) , (various) , - , CD (2×10⁻¹²%) , ²⁰⁸Pb
²⁸Mg , - , β⁺β⁺ (rare) , ²³⁶U , - , rowspan=2, ²³⁷Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 143 , rowspan=2, 237.0484097(24) , rowspan=2, 45.2(1) d , EC , ²³⁷Np , rowspan=2, 7/2− , rowspan=2, , - , α (.0042%) , ²³³U , - , style="text-indent:1em" , ^237m1Pu , colspan="3" style="text-indent:2em" , 145.544(10)2 keV , 180(20) ms , IT , ²³⁷Pu , 1/2+ , , - , style="text-indent:1em" , ^237m2Pu , colspan="3" style="text-indent:2em" , 2900(250) keV , 1.1(1) μs , , , , , - , rowspan=4, ²³⁸Pu , rowspan=4 style="text-align:right" , 94 , rowspan=4 style="text-align:right" , 144 , rowspan=4, 238.0495599(20) , rowspan=4, 87.7(1) y , α , ²³⁴U , rowspan=4, 0+ , rowspan=4, 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 clos ...

product of ²³⁸U , - , SF (1.9×10⁻⁷%) , (various) , - , CD (1.4×10⁻¹⁴%) , ²⁰⁶Hg
³²Si , - , CD (6×10⁻¹⁵%) , ¹⁸⁰Yb
³⁰Mg
²⁸Mg , - , rowspan=2, ²³⁹Pufissile nuclideMost useful isotope for nuclear weapons , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 145 , rowspan=2, 239.0521634(20) , rowspan=2, 2.411(3)×10⁴ y , α , ''²³⁵U'' , 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, ...

product of ²³⁸U , - , SF (3.1×10⁻¹⁰%) , (various) , - , style="text-indent:1em" , ^239m1Pu , colspan="3" style="text-indent:2em" , 391.584(3) keV , 193(4) ns , , , 7/2− , , - , style="text-indent:1em" , ^239m2Pu , colspan="3" style="text-indent:2em" , 3100(200) keV , 7.5(10) μs , , , (5/2+) , , - , rowspan=3, ²⁴⁰Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 146 , rowspan=3, 240.0538135(20) , rowspan=3, 6.561(7)×10³ y , α , ²³⁶U , rowspan=3, 0+ , rowspan=3, TraceIntermediate decay product of ²⁴⁴Pu , - , SF (5.7×10⁻⁶%) , (various) , - , CD (1.3×10⁻¹³%) , ²⁰⁶Hg
³⁴Si , - , rowspan=3, ²⁴¹Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 147 , rowspan=3, 241.0568515(20) , rowspan=3, 14.290(6) y , β⁻ (99.99%) , ²⁴¹Am , rowspan=3, 5/2+ , rowspan=3, , - , α (.00245%) , ²³⁷U , - , SF (2.4×10⁻¹⁴%) , (various) , - , style="text-indent:1em" , ^241m1Pu , colspan="3" style="text-indent:2em" , 161.6(1) keV , 0.88(5) μs , , , 1/2+ , , - , style="text-indent:1em" , ^241m2Pu , colspan="3" style="text-indent:2em" , 2200(200) keV , 21(3) μs , , , , , - , rowspan=2, ²⁴²Pu , rowspan=2 style="text-align:right" , 94 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 242.0587426(20) , rowspan=2, 3.75(2)×10⁵ y , α , ''²³⁸U'' , rowspan=2, 0+ , rowspan=2, , - , SF (5.5×10⁻⁴%) , (various) , - , ²⁴³Pu , style="text-align:right" , 94 , style="text-align:right" , 149 , 243.062003(3) , 4.956(3) h , β⁻ , ²⁴³Am , 7/2+ , , - , style="text-indent:1em" , ^243mPu , colspan="3" style="text-indent:2em" , 383.6(4) keV , 330(30) ns , , , (1/2+) , , - , rowspan=3, ²⁴⁴Pu , rowspan=3 style="text-align:right" , 94 , rowspan=3 style="text-align:right" , 150 , rowspan=3, 244.064204(5) , rowspan=3, 8.00(9)×10⁷ y , α (99.88%) , ²⁴⁰U , rowspan=3, 0+ , rowspan=3, TraceInterstellar, some may also be primordial but such claims are disputed , - , SF (.123%) , (various) , - , β⁻β⁻ (7.3×10⁻⁹%) , ²⁴⁴Cm , - , ²⁴⁵Pu , style="text-align:right" , 94 , style="text-align:right" , 151 , 245.067747(15) , 10.5(1) h , β⁻ , ²⁴⁵Am , (9/2−) , , - , ²⁴⁶Pu , style="text-align:right" , 94 , style="text-align:right" , 152 , 246.070205(16) , 10.84(2) d , β⁻ , ^246mAm , 0+ , , - , ²⁴⁷Pu , style="text-align:right" , 94 , style="text-align:right" , 153 , 247.07407(32)# , 2.27(23) d , β⁻ , ²⁴⁷Am , 1/2+# ,

Actinides vs fission products

Notable isotopes

Plutonium-238 Plutonium-238 (238Pu or Pu-238) is a fissile, 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 suitab ...

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 ²³⁸Pu for

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioacti ...

s that power some

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

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 s ...

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 an ...

can contain as much as a few percent ²³⁸Pu, originating from ²³⁷Np,

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...

of ²⁴²Cm, or (n,2n) reactions. *

Plutonium-239 Plutonium-239 (239Pu 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 ...

is the most important isotope of plutonium, with a half-life of 24,100 years. ²³⁹Pu and ²⁴¹Pu are

fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...

, meaning that the nuclei of their atoms can break apart by being bombarded by slow moving thermal neutrons, releasing energy,

gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

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 of these reactions. The specific nu ...

, leading to applications in

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

s and

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...

s. ²³⁹Pu is synthesized by irradiating

uranium-238 Uranium-238 (238U 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 ...

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. 240 ...

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 Neutron capture, react with Atomic nucleus, nuclei of other ...

of plutonium containing it. Plutonium is graded by proportion of ²⁴⁰Pu:

weapons grade Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon or has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nucle ...

(< 7%), fuel grade (7–19%) and reactor grade (> 19%). Lower grades are less suited for nuclear weapons 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 struct ...

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 or greater, on average), as opposed t ...

s. *

Plutonium-241 Plutonium-241 (241Pu 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 t ...

is fissile, but also

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

s with a half-life of 14 years to

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

. *

Plutonium-242 Plutonium-242 (242Pu or Pu-242) is one of the isotopes of plutonium, the second longest-lived, with a half-life of 375,000 years. The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the la ...

is not fissile, not very fertile (requiring 3 more neutron captures to become fissile), has a low neutron capture

cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...

, and a longer half-life than any of the lighter isotopes. *

Plutonium-244 Plutonium-244 (244Pu) is an isotope of plutonium that has a half-life of 80 million years. This is longer than any of the other isotopes of plutonium and longer than any other actinide isotope except for the three naturally abundant ones: uranium ...

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 ²⁴³Pu has a short half-life, but some is produced in nuclear explosions. Plutonium-244 has been found in interstellar space and is has the longest half-life of any non-primordial radioisotope.

Production and uses

²³⁹Pu, a fissile isotope that is the second most used

nuclear fuel Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...

in nuclear reactors after

uranium-235 Uranium-235 (235U 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 exis ...

, and the most used fuel in the fission portion of

s, is produced from

by neutron capture followed by two beta decays. ²⁴⁰Pu, ²⁴¹Pu, and ²⁴²Pu are produced by further neutron capture. The odd-mass isotopes ²³⁹Pu and ²⁴¹Pu 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 with ...

and about a 1/4 chance of retaining the

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

and becoming the next heavier isotope. The even-mass isotopes are

fertile material Fertile material is a material that, although not itself fissionable by thermal neutrons, can be converted into a fissile material by neutron absorption and subsequent nuclei conversions. Naturally occurring fertile materials Naturally occurring ...

but not fissile and also have a lower overall probability (

) 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) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a electric generator, generato ...

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

MOX fuel Mixed oxide fuel, commonly referred to as 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 alt ...

, ²⁴⁰Pu may even be the most common isotope. All plutonium isotopes and other

actinide The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...

s, however, are

fissionable In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typi ...

with

fast 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 with ...

s. ²⁴⁰Pu does have a moderate thermal neutron absorption cross section, so that ²⁴¹Pu production in a thermal reactor becomes a significant fraction as large as ²³⁹Pu production. ²⁴¹Pu has a half-life of 14 years, and has slightly higher thermal neutron cross sections than ²³⁹Pu for both fission and absorption. While nuclear fuel is being used in a reactor, a ²⁴¹Pu nucleus is much more likely to fission or to capture a neutron than to decay. ²⁴¹Pu accounts for a significant proportion 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 ²⁴¹Pu will beta decay to

, one of the

minor actinide The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkeliu ...

s, a strong alpha emitter, and difficult to use in thermal reactors. ²⁴²Pu has a particularly low cross section for thermal neutron capture; and it takes three neutron absorptions to become another fissile isotope (either

curium Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...

-245 or ²⁴¹Pu) 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 radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding ...

, which is a neutron emitter by spontaneous fission and difficult to handle) or becoming ²⁴²Pu again; so the mean number of neutrons absorbed before fission is even higher than 3. Therefore, ²⁴²Pu is particularly unsuited to recycling in a thermal reactor and would be better used in a

where it can be fissioned directly. However, ²⁴²Pu's low cross section means that relatively little of it will be transmuted during one cycle in a thermal reactor. ²⁴²Pu's half-life is about 15 times as long as ²³⁹Pu'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. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...

radioactivity. ²⁴²Pu's

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

emissions are also weaker than those of the other isotopes. ²⁴³Pu has a half-life of only 5 hours, beta decaying to

americium-243 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 ...

. Because ²⁴³Pu has little opportunity to capture an additional neutron before decay, the

nuclear fuel cycle The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the ''front end'', which are the preparation of the fuel, steps in the ''service period'' in w ...

does not produce the long-lived ²⁴⁴Pu in significant quantity. ²³⁸Pu 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 ²³⁸Pu relatively free of other plutonium isotopes for use in

s), by the (n,2n) reaction of fast neutrons on ²³⁹Pu, or by alpha decay of

-242, which is produced by neutron capture from ²⁴¹Am. It has significant thermal neutron cross section for fission, but is more likely to capture a neutron and become ²³⁹Pu.

Manufacture

Plutonium-240, -241 and -242

The fission

for ²³⁹Pu is 747.9

barns A barn is an agricultural building usually on farms and used for various purposes. In North America, a barn refers to structures that house livestock, including cattle and horses, as well as equipment and fodder, and often grain.Allen G. ...

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

plutonium.

Plutonium-239

Plutonium-239 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 (233U or U-233) is a fissile Isotopes of uranium, 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 ha ...

. Plutonium-239 is virtually nonexistent in nature. It is made by bombarding

with neutrons in a nuclear reactor. Uranium-238 is present in quantity in most reactor fuel; hence plutonium-239 is continuously made in these reactors. Since plutonium-239 can itself be split by neutrons to release energy, plutonium-239 provides a portion of the energy generation in a nuclear reactor. Plutonium ring

Plutonium-238

There are small amounts of ²³⁸Pu in the plutonium of usual plutonium-producing reactors. However, isotopic separation would be quite expensive compared to another method: when a ²³⁵U atom captures a neutron, it is converted to an excited state of ²³⁶U. Some of the excited ²³⁶U nuclei undergo fission, but some decay to the ground state of ²³⁶U by emitting gamma radiation. Further neutron capture creates ²³⁷U, which has a half-life of 7 days and thus quickly decays to ²³⁷Np. Since nearly all neptunium is produced in this way or consists of isotopes that decay quickly, one gets nearly pure ²³⁷Np by chemical separation of neptunium. After this chemical separation, ²³⁷Np is again irradiated by reactor neutrons to be converted to ²³⁸Np, which decays to ²³⁸Pu with a half-life of 2 days.

²⁴⁰Pu as an obstacle to nuclear weapons

undergoes spontaneous fission as a secondary decay mode at a small but significant rate. The presence of ²⁴⁰Pu 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 bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb ...

, because the neutron flux from spontaneous fission initiates 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 syst ...

prematurely, causing an early release of energy that physically 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 power. Plutonium consisting of more than about 90% ²³⁹Pu is called

weapons-grade plutonium Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon or has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium Uranium is a chemical eleme ...

; plutonium from

from commercial power reactors generally contains at least 20% ²⁴⁰Pu and is called

reactor-grade plutonium Reactor-grade plutonium (RGPu) is the isotopic grade of plutonium that is found in spent nuclear fuel after the uranium-235 primary fuel that a nuclear power reactor uses has burnt up. The uranium-238 from which most of the plutonium isotopes der ...

. 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 fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released d ...

, 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 when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produ ...

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. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a t ...

, 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. ²⁴⁰Pu contamination is the reason plutonium weapons must use the implosion method. Theoretically, pure ²³⁹Pu could be used in a

gun-type nuclear weapon Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another. Although this is someti ...

, but achieving this level of purity is prohibitively difficult. ²⁴⁰Pu contamination has proven a mixed blessing to

nuclear weapons design Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types: * pure fission weapons, the simplest and least technically ...

. While it created delays and headaches during the

Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

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

nuclear proliferation Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as " Nuclear Weapon States" by the Treaty on the Non-Proliferation of Nuclear Wea ...

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

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Authority control Plutonium