HOME

TheInfoList




Plutonium is a
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 ...

radioactive
chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, eleme ...
with the
symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. All (and ) is achieved th ...
Pu and
atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one ...
94. It is an
actinide The actinoid (, also called actinide ) series encompasses the 15 metallic s with s from 89 to 103, through . The actinoid series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in gener ...
metal A metal (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mi ...

metal
of silvery-gray appearance that
tarnish Tarnish is a thin layer of corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide of rutile. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds ...
es when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six
allotrope Allotropy or allotropism () is the property of some chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting o ...
s and four
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge' ...
s. It reacts with
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
,
halogen The halogens () are a group A group is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can b ...

halogen
s,
nitrogen Nitrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

nitrogen
,
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
, and
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
. When exposed to moist air, it forms
oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
s and
hydride In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...

hydride
s that can expand the sample up to 70% in volume, which in turn flake off as a powder that is
pyrophoric A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are iron sulfid ...
. It is radioactive and can accumulate in
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
s, which makes the handling of plutonium dangerous. Plutonium was first synthetically produced and isolated in late 1940 and early 1941, by a
deuteron Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element ...

deuteron
bombardment of
uranium-238 Uranium-238 (238U or U-238) is the most common isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Electric ...
in the
cyclotron . The magnet is painted yellow. A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it wa ...

cyclotron
at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of California ...

University of California, Berkeley
. First,
neptunium-238 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 synt ...
(
half-life Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents an ...
2.1 days) was synthesized, which subsequently
beta-decayed
beta-decayed
to form the new element with atomic number 94 and atomic weight 238 (half-life 88 years). Since
uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

uranium
had been named after the planet
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus, who, according to Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and ...

Uranus
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 ...

neptunium
after the planet
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mor ...

Neptune
, element 94 was named after
Pluto Pluto (minor-planet designation A formal minor planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur (minor planet), centaur, trans-Neptunian object and dwarf planet but not comet ...

Pluto
, which at the time was considered to be a planet as well. Wartime secrecy prevented the University of California team from publishing its discovery until 1948. Plutonium is the element with the highest atomic number to occur in nature. Trace quantities arise in natural uranium-238 deposits when uranium-238 captures neutrons emitted by decay of other uranium-238 atoms. Both
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but differe ...

plutonium-239
and
plutonium-241 Plutonium-241 (241Pu, Pu-241) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different ...

plutonium-241
are
fissile In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, veh ...
, meaning that they can sustain a
nuclear chain reaction 300px, A possible nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron">uranium-235.html" ;"title="nuclear fission chain reaction: 1) A uranium-235">nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron, ...
, leading to applications in
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics and nucl ...
s and
nuclear reactor A nuclear reactor, formerly known as an atomic pile, 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 nucle ...

nuclear reactor
s.
Plutonium-240 Plutonium-240 (, Pu-240) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numb ...

Plutonium-240
exhibits a high rate of
spontaneous fission Spontaneous fission (SF) is a form of radioactive decay 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 r ...
, raising the
neutron flux The neutron flux, φ, is a scalar quantity used in nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are also studied. Nuclear physics shou ...
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
grade Grade or grading may refer to: Arts and entertainment * Grade (band) Grade is a melodic hardcore band from Canada, often credited as pioneers in blending metallic hardcore with the hon and melody of emo, and - most notably - the alternating scr ...
(
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 nuclear ...
, fuel-grade, or reactor-grade).
Plutonium-238 Plutonium-238 (238Pu) is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the sma ...

Plutonium-238
has a half-life of 87.7 years and emits
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proton ...
s. It is a heat source in
radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG) is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive Radioactive decay (also known as nuclear decay, radi ...
s, which are used to power some
spacecraft File:Space Shuttle Columbia launching.jpg, 275px, The US Space Shuttle flew 135 times from 1981 to 2011, supporting Spacelab, ''Mir'', the Hubble Space Telescope, and the ISS. (''Columbia'' STS-1, maiden launch, which had a white external tank, ...

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 The Manhattan Project was a research and development Research is " creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization, and analysis of information to increase understa ...
during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a that lasted from 1939 to 1945. It involved —including all of the great powers—forming two opposing s: the and the . In a total war directly involving m ...
that developed the first atomic bombs. The
Fat Man "Fat Man" (also known as Mark III) is the codename for the type of nuclear bomb A nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, or nuclear bomb) is an explosive device that derives its destructive f ...

Fat Man
bombs used in the
Trinity The Christian Christians () are people who follow or adhere to Christianity, a monotheistic Abrahamic religion based on the life and teachings of Jesus in Christianity, Jesus Christ. The words ''Christ (title), Christ'' and ''Christian' ...
nuclear test Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield Yield may refer to: Measures of output/function Computer science * Yield (multithreading) is an action that occurs in a computer program duri ...
in July 1945, and in the bombing of Nagasaki in August 1945, had plutonium cores.
Human radiation experiments Since the discovery of ionizing radiation Ionizing radiation (ionising radiation) consists of subatomic particles or electromagnetic waves that have sufficient energy to ionization, ionize atoms or molecules by detaching electrons from them. Th ...
studying plutonium were conducted without
informed consent Informed consent is a principle in medical ethics Medical ethics is an applied branch of ethics which analyzes the practice of clinical medicine and related scientific research. Medical ethics is based on a set of values that professionals can refe ...
, and several
criticality accident A criticality accident is an uncontrolled nuclear fission chain reaction. It is sometimes referred to as a critical excursion, critical power excursion, or divergent chain reaction. Any such event involves the unintended accumulation or arrangeme ...
s, some lethal, occurred after the war. Disposal of plutonium waste from
nuclear power plant A nuclear power plant (sometimes abbreviated as NPP) is a thermal power station A thermal power station is a power station in which heat energy is converted to electricity. Typically, fuel is used to boil water in a large pressure vessel to ...

nuclear power plant
s and dismantled nuclear weapons built during the
Cold War The Cold War was a period of tension between the and the and their respective allies, the and the , which began following . Historians do not fully agree on its starting and ending points, but the period is generally considered to span ...
is a
nuclear-proliferation
nuclear-proliferation
and environmental concern. Other sources of plutonium in the environment are
fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear explosion, nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refer ...
from numerous above-ground nuclear tests, now
banned A ban is a formal or informal prohibition Prohibition is the act or practice of forbidding something by law; more particularly the term refers to the banning of the manufacture, storage (whether in barrel A barrel or cask is a hollow cy ...
.


Characteristics


Physical properties

Plutonium, like most metals, has a bright silvery appearance at first, much like
nickel Nickel is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

nickel
, but it
oxidizes (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, th ...
very quickly to a dull gray, although yellow and olive green are also reported. (public domain text) At room temperature plutonium is in its α (''alpha'') form. This, the most common structural form of the element (
allotrope Allotropy or allotropism () is the property of some chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting o ...
), is about as hard and brittle as
gray cast iron Gray iron, or grey cast iron, is a type of cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour ...
unless it is
alloy An alloy is an admixture of metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in ...
ed with other metals to make it soft and ductile. Unlike most metals, it is not a good conductor of
heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

heat
or
electricity Electricity is the set of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Physi ...
. It has a low
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can b ...

melting point
(640 °C) and an unusually high
boiling point The boiling point of a substance is the temperature at which the vapor pressure 280px, The ''pistol test tube'' experiment. The tube contains alcohol and is closed with a piece of cork. By heating the alcohol, the vapors fill in the space, inc ...
(3,228 °C). , the release of a high-energy
helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining" ...

helium
nucleus, is the most common form of
radioactive decay 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 ...

radioactive decay
for plutonium. A 5 kg mass of 239Pu contains about atoms. With a half-life of 24,100 years, about of its atoms decay each second by emitting a 5.157 
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
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.
Resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
is a measure of how strongly a material opposes the flow of
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
. The 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. This trend continues down to 100 , below which resistivity rapidly decreases for fresh samples. Resistivity then begins to increase with time at around 20 K due to radiation damage, with the rate dictated by the isotopic composition of the sample. Because of self-irradiation, a sample of plutonium fatigues throughout its crystal structure, meaning the ordered arrangement of its atoms becomes disrupted by radiation with time. Self-irradiation can also lead to annealing which counteracts some of the fatigue effects as temperature increases above 100 K. 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. Near the melting point, the liquid plutonium has very high
viscosity The viscosity of a is a measure of its to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, has a higher viscosity than . Viscosity can be conceptualized as quantifying the inter ...

viscosity
and
surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Gerridae, water strid ...

surface tension
compared to other metals.


Allotropes

Plutonium normally has six
allotrope Allotropy or allotropism () is the property of some chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting o ...
s and forms a seventh (zeta, ζ) at high temperature within a limited pressure range. These allotropes, which are different structural modifications or forms of an element, have very similar internal energies but significantly varying
densities The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter Rho (letter), rho), although the L ...

densities
and
crystal structure In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "col ...

crystal structure
s. This makes plutonium very sensitive to changes in temperature, pressure, or chemistry, and allows for dramatic volume changes following
phase transition In , , and many other related fields, phase transitions (or phase changes) are the of transition between a state of a medium, identified by some parameters, and another one, with different values of the parameters. Commonly the term is used to ...
s from one allotropic form to another. The densities of the different allotropes vary from 16.00 g/cm3 to 19.86 g/cm3. 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 Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impuritie ...
but changes to the plastic and malleable β (''beta'') form at slightly higher temperatures. The reasons for the complicated phase diagram are not entirely understood. The α form has a low-symmetry
monoclinic In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' " ...
structure, hence its brittleness, strength, compressibility, and poor thermal conductivity. Plutonium in the δ (''delta'') form normally exists in the 310 °C to 452 °C range but is stable at room temperature when alloyed with a small percentage of
gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic table and is ...

gallium
,
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
, or
cerium Cerium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that ...

cerium
, enhancing workability and allowing it to be
welded Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing Fusion welding, fusion. Welding is distinct from lower ...

welded
. The δ form has more typical metallic character, and is roughly as strong and malleable as aluminium. In fission weapons, the explosive
shock wave of an attached shock on a sharp-nosed supersonic F/A-18F Super Hornet in transonic flight Flight or flying is the process by which an object (physics), object motion (physics), moves through a space without contacting any planetary surfac ...
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 A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its atomic nucleus, nuclear properties (specifically, its nuclear fission nuclear c ...
. The ε phase, the highest temperature solid allotrope, exhibits anomalously high atomic
self-diffusionAccording to IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Cou ...
compared to other elements.


Nuclear fission

Plutonium is a radioactive
actinide The actinoid (, also called actinide ) series encompasses the 15 metallic s with s from 89 to 103, through . The actinoid series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in gener ...
metal whose
isotope Isotopes are two or more types of atoms that have the same atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of ...
,
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but differe ...

plutonium-239
, is one of the three primary
fissile In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, veh ...
isotopes (
uranium-233 Uranium-233 (233U) 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 has been use ...

uranium-233
and
uranium-235 Uranium-235 (235U) is an Isotopes of uranium, 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 th ...

uranium-235
are the other two);
plutonium-241 Plutonium-241 (241Pu, Pu-241) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different ...

plutonium-241
is also highly fissile. To be considered fissile, an isotope's
atomic nucleus The atomic nucleus is the small, dense region consisting of s and s at the center of an , discovered in 1911 by based on the 1909 . After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickl ...
must be able to break apart or
fission Fission, a splitting of something into two or more parts, may refer to: Biology * Fission (biology), division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original * Mitochondri ...

fission
when struck by a slow moving neutron and to release enough additional neutrons to sustain the
nuclear chain reaction 300px, A possible nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron">uranium-235.html" ;"title="nuclear fission chain reaction: 1) A uranium-235">nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron, ...
by splitting further nuclei. Pure plutonium-239 may have a four factor formula, multiplication factor (keff) 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. During fission, a fraction of the nuclear binding energy, which holds a nucleus together, is released as a large amount of 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 . It is this energy that makes plutonium-239 useful in
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics and nucl ...
s and nuclear reactor, reactors. The presence of the isotope plutonium-240 in a sample limits its nuclear bomb potential, as plutonium-240 has a relatively high
spontaneous fission Spontaneous fission (SF) is a form of radioactive decay 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 r ...
rate (~440 fissions per second per gram—over 1,000 neutrons per second per gram), raising the background neutron levels and thus increasing the risk of fizzle (nuclear test), predetonation. Plutonium is identified as either
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 nuclear ...
, fuel-grade, or reactor-grade based on the percentage of plutonium-240 that it contains. Weapons-grade plutonium contains less than 7% plutonium-240. reactor-grade plutonium, Fuel-grade plutonium contains from 7% to less than 19%, and power reactor-grade contains 19% or more plutonium-240. plutonium-239#Supergrade plutonium, Supergrade plutonium, with less than 4% of plutonium-240, is used in United States Navy, U.S. Navy weapons stored in proximity to ship and submarine crews, due to its lower radioactivity. The isotope plutonium-238 is not fissile#Fissile vs fissionable, fissile but can undergo nuclear fission easily with fast neutrons as well as alpha decay.


Isotopes and nucleosynthesis

Twenty radioisotope, radioactive isotopes of plutonium have been characterized. The longest-lived are plutonium-244, with a half-life of 80.8 million years, plutonium-242, with a half-life of 373,300 years, and plutonium-239, with a half-life of 24,110 years. All of the remaining radioactive isotopes have half-lives that are less than 7,000 years. This element also has eight meta state, metastable states, though all have half-lives less than one second. The known isotopes of plutonium range in mass number from 228 to 247. The primary decay modes of isotopes with mass numbers lower than the most stable isotope, plutonium-244, are spontaneous fission and alpha emission, mostly forming uranium (92 protons) 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 ...

neptunium
(93 protons) isotopes as decay products (neglecting the wide range of daughter nuclei created by fission processes). The primary decay mode for isotopes with mass numbers higher than plutonium-244 is beta emission, mostly forming americium (95 protons) isotopes as decay products. Plutonium-241 is the parent isotope of the neptunium decay series, decaying to americium-241 via beta emission. Plutonium-238 and 239 are the most widely synthesized isotopes. Plutonium-239 is synthesized via the following reaction using uranium (U) and neutrons (n) via beta decay (β) with neptunium (Np) as an intermediate: : + -> ->[\beta^-] [23.5 \ \ce] ->[\beta^-] [2.3565 \ \ce d] 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 days) and another beta decay forms plutonium-239. Egon Bretscher working on the British Tube Alloys project predicted this reaction theoretically in 1940. Plutonium-238 is synthesized by bombarding uranium-238 with deuterons (D, the nuclei of heavy
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
) in the following reaction: :\begin \ce &\ce \\ &\ce \end In this process, a deuteron hitting uranium-238 produces two neutrons and neptunium-238, which spontaneously decays by emitting negative beta particles to form plutonium-238.


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.


Compounds and chemistry

At room temperature, pure plutonium is silvery in color but gains a tarnish when oxidized. The element displays four common ionic
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge' ...
s in aqueous solution and one rare one: * Pu(III), as Pu3+ (blue lavender) * Pu(IV), as Pu4+ (yellow brown) * Pu(V), as (light pink) * Pu(VI), as (pink orange) * Pu(VII), as (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. 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)] [PuIICp″3], Cp″ = C5H3(SiMe3)2. A +8 oxidation state is possible as well in the volatile tetroxide . Though it readily decomposes via a reduction mechanism similar to , can be stabilized in alkaline solutions and chloroform. Metallic plutonium is produced by reacting plutonium tetrafluoride with barium, calcium or lithium at 1200 °C. Metallic plutonium is attacked by acids, oxygen, and steam but not by alkalis and dissolves easily in concentrated hydrochloric acid, hydrochloric, hydroiodic acid, hydroiodic and perchloric acids. Molten metal must be kept in a vacuum or an inert atmosphere to avoid reaction with air. At 135 °C the metal will ignite in air and will explode if placed in carbon tetrachloride. Plutonium is a reactive metal. In moist air or moist argon, the metal oxidizes rapidly, producing a mixture of
oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
s and
hydride In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...

hydride
s. If the metal is exposed long enough to a limited amount of water vapor, a powdery surface coating of PuO2 is formed. Also formed is plutonium hydride but an excess of water vapor forms only PuO2. Plutonium shows enormous, and reversible, reaction rates with pure hydrogen, forming plutonium hydride. It also reacts readily with oxygen, forming PuO and PuO2 as well as intermediate oxides; plutonium oxide fills 40% more volume than plutonium metal. The metal reacts with the
halogen The halogens () are a group A group is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can b ...

halogen
s, giving rise to chemical compound, compounds with the general formula PuX3 where X can be plutonium(III) fluoride, F, plutonium(III) chloride, Cl, Br or I and PuF4 is also seen. The following oxyhalides are observed: PuOCl, PuOBr and PuOI. It will react with carbon to form PuC, nitrogen to form PuN and
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
to form PuSi2. The Organometallic chemistry, organometallic chemistry of plutonium complexes is typical for Organoactinide chemistry, organoactinide species; a characteristic example of an organoplutonium compound is plutonocene. Computational chemistry methods indicate an enhanced Covalent bond, covalent character in the plutonium-ligand bonding. Powders of plutonium, its hydrides and certain oxides like Pu2O3 are
pyrophoric A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are iron sulfid ...
, 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 °C. Pu2O3 spontaneously heats up and transforms into PuO2, which is stable in dry air, but reacts with water vapor when heated. Crucibles 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, borides, carbides, nitrides and silicides 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. Cerium is used as a chemical simulant of plutonium for development of containment, extraction, and other technologies.


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. 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 5fn7s2 and 5fn−16d17s2 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.


Alloys

Plutonium can form alloys and intermediate compounds with most other metals. Exceptions include lithium, sodium, potassium, rubidium and caesium of the alkali metals; and magnesium, calcium, strontium, and barium of the alkaline earth metals; and europium and ytterbium of the rare earth metals. 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. Gallium, aluminium, americium, scandium and cerium can stabilize the δ phase of 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. Plutonium alloys can be produced by adding a metal to molten plutonium. If the alloying metal is sufficiently reductive, plutonium can be added in the form of oxides or halides. The δ phase plutonium–gallium and plutonium–aluminium alloys are produced by adding plutonium(III) fluoride to molten gallium or aluminium, which has the advantage of avoiding dealing directly with the highly reactive plutonium metal. * Plutonium-gallium alloy, Plutonium–gallium 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 nuclear weapons. * Plutonium–aluminium is an alternative to the Pu–Ga alloy. 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 weapon pits. Plutonium–aluminium alloy can be also used as a component of nuclear fuel. * Plutonium–gallium–cobalt alloy (PuCoGa5) is an unconventional superconductor, showing superconductivity below 18.5 K, an order of magnitude higher than the highest between heavy fermion systems, and has large critical current. * Plutonium–zirconium alloy can be used as nuclear fuel. * Plutonium–cerium and plutonium–cerium–cobalt alloys are used as nuclear fuels. * Plutonium–uranium, with about 15–30 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. * 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. * Thorium–uranium–plutonium was investigated as a nuclear fuel for fast breeder reactors.


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, such as the natural nuclear fission reactor in Oklo, Gabon. The ratio of plutonium-239 to uranium at the Cigar Lake Mine uranium deposit ranges from to . These trace amounts of 239Pu originate in the following fashion: on rare occasions, 238U 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 238U atom, it is absorbed by the atom, which becomes 239U. With a relatively short half-life, 239U decays to 239Np, which decays into 239Pu. 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. Due to its relatively long half-life of about 80 million years, it was suggested that plutonium-244 occurs naturally as a primordial nuclide, but early reports of its detection could not be confirmed. However, its long half-life ensured its circulation across the solar system before its extinct radionuclide, extinction, and indeed, evidence of the spontaneous fission of extinct 244Pu has been found in meteorites. The former presence of 244Pu in the early Solar System has been confirmed, since it manifests itself today as an excess of its daughters, either 232thorium, Th (from the alpha decay pathway) or xenon isotopes (from its
spontaneous fission Spontaneous fission (SF) is a form of radioactive decay 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 r ...
). 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. 244Pu has the longest half-life of all transuranic nuclides and is produced only in the r-process in supernovae and colliding neutron stars; when nuclei are ejected from these events at high speed to reach Earth, 244Pu alone among transuranic nuclides has a long enough half-life to survive the journey, and hence tiny traces of live interstellar 244Pu have been found in the deep sea floor. Because 240Pu also occurs in the decay chain of 244Pu, it must thus also be present in secular equilibrium, albeit in even tinier quantities. 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. Most atmospheric and underwater nuclear testing was stopped by the Limited Test Ban Treaty in 1963, which was signed and ratified by the United States, the United Kingdom, the Soviet Union, and other nations. Continued atmospheric nuclear weapons testing since 1963 by non-treaty nations included those by China (atomic bomb test above the Gobi Desert in 1964, hydrogen bomb test in 1967, and follow-on tests), and France (tests as recently as the 1990s). Because it is deliberately manufactured for nuclear weapons and nuclear reactors, plutonium-239 is the most abundant isotope of plutonium by far.


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. Fermi called the element ''hesperium'' and mentioned it in his Nobel Lecture in 1938. The sample actually contained products of nuclear fission, primarily barium and krypton. Nuclear fission, discovered in Germany in 1938 by Otto Hahn and Fritz Strassmann, was unknown at the time. 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
cyclotron . The magnet is painted yellow. A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it wa ...

cyclotron
at the Berkeley Radiation Laboratory at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of California ...

University of California, Berkeley
. 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. 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. A paper documenting the discovery was prepared by the team and sent to the journal ''Physical Review'' in March 1941, but publication was delayed until a year after the end of
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a that lasted from 1939 to 1945. It involved —including all of the great powers—forming two opposing s: the and the . In a total war directly involving m ...
due to security concerns. 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. McMillan had recently named the first transuranic element neptunium after the planet
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mor ...

Neptune
, and suggested that element 94, being the next element in the series, be named for what was then considered the next planet,
Pluto Pluto (minor-planet designation A formal minor planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur (minor planet), centaur, trans-Neptunian object and dwarf planet but not comet ...

Pluto
. Nicholas Kemmer of the Cambridge team independently proposed the same name, based on the same reasoning as the Berkeley team. Seaborg originally considered the name "plutium", but later thought that it did not sound as good as "plutonium". 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. 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. 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 becquerels).


Early research

The chemistry of plutonium was found to resemble uranium after a few months of initial study. 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 micrograms of plutonium-239 combined with uranium and fission products was produced and only about 1 microgram was isolated. This procedure enabled chemists to determine the new element's atomic weight. 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. In November 1943 some plutonium trifluoride was reduced to create the first sample of plutonium metal: a few micrograms of metallic beads. Enough plutonium was produced to make it the first synthetically made element to be visible with the unaided eye. 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. 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.


Production during the Manhattan Project

During World War II the U.S. government established the
Manhattan Project The Manhattan Project was a research and development Research is " creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization, and analysis of information to increase understa ...
, which was tasked with 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 laboratory, now known as Los Alamos National Laboratory. The first production reactor that made plutonium-239 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. 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. On April 5, 1944, Emilio Segrè at Los Alamos received the first sample of reactor-produced plutonium from Oak Ridge. Within ten days, he discovered that reactor-bred plutonium had a higher concentration of the isotope plutonium-240 than cyclotron-produced plutonium. Plutonium-240 has a high spontaneous fission rate, raising the overall background neutron level of the plutonium sample. The original gun-type fission weapon, 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. The entire plutonium weapon design effort at Los Alamos was soon changed to the more complicated implosion device, code-named "
Fat Man "Fat Man" (also known as Mark III) is the codename for the type of nuclear bomb A nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, or nuclear bomb) is an explosive device that derives its destructive f ...

Fat Man
". With an implosion weapon, plutonium is compressed to a high density with explosive lenses—a technically more daunting task than the simple gun-type design, but necessary to use plutonium for weapons purposes. Enriched uranium, by contrast, can be used with either method. 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. B, D and F were the initial reactors built at Hanford, and six additional plutonium-producing reactors were built later at the site. 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. 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". 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. 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.


Trinity and Fat Man atomic bombs

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. The implosion design of "Trinity (nuclear test)#The Gadget, the gadget", as the Trinity device was code-named, used conventional explosive lenses to compress a sphere of plutonium into a supercritical mass, which was simultaneously showered with neutrons from the Urchin (detonator), "Urchin", an initiator made of polonium and beryllium (neutron source: Neutron source#Small sized devices, (α, n) reaction). Together, these ensured a runaway chain reaction and explosion. The overall weapon weighed over 4 tonnes, although it used just 6.2 kg of plutonium in its core. About 20% of the plutonium used in the Trinity weapon underwent fission, resulting in an explosion with an energy equivalent to approximately 20,000 tons of TNT. An identical design was used in the "Fat Man" atomic bomb dropped on Nagasaki, Japan, on August 9, 1945, killing 35,000–40,000 people and destroying 68%–80% of war production at Nagasaki. 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.


Cold War use and waste

Large stockpiles of weapons-grade plutonium were built up by both the Soviet Union and the United States during the
Cold War The Cold War was a period of tension between the and the and their respective allies, the and the , which began following . Historians do not fully agree on its starting and ending points, but the period is generally considered to span ...
. The U.S. reactors at Hanford and the Savannah River Site in South Carolina produced 103 tonnes, and an estimated 170 tonnes of military-grade plutonium was produced in the USSR. Each year about 20 tonnes of the element is still produced as a by-product of the nuclear power industry. As much as 1000 tonnes of plutonium may be in storage with more than 200 tonnes of that either inside or extracted from nuclear weapons. SIPRI estimated the world plutonium stockpile in 2007 as about 500 tonnes, divided equally between weapon and civilian stocks. 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". 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." Reprinted in 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. In the U.S., some plutonium extracted from dismantled nuclear weapons is melted to form glass logs of plutonium oxide that weigh two tonnes. The glass is made of borosilicates mixed with cadmium and gadolinium. These logs are planned to be encased in stainless steel and stored as much as underground in bore holes that will be back-filled with concrete. The U.S. planned to store plutonium in this way at the Yucca Mountain nuclear waste repository, which is about north-east of Las Vegas, Nevada. 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". 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. In their final report the Commission put forth recommendations for developing a comprehensive strategy to pursue, including: : "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".


Medical experimentation

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. Animal studies found that a few milligrams of plutonium per kilogram of tissue is a lethal dose. In the case of human subjects, this involved injecting solutions containing (typically) five micrograms 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 condition. This was reduced to one microgram in July 1945 after animal studies found that the way plutonium distributed itself in bones was more dangerous than radium. Most of the subjects, Eileen Welsome says, were poor, powerless, and sick. From 1945 to 1947, eighteen human test subjects were injected with plutonium without
informed consent Informed consent is a principle in medical ethics Medical ethics is an applied branch of ethics which analyzes the practice of clinical medicine and related scientific research. Medical ethics is based on a set of values that professionals can refe ...
. 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. Ebb Cade was an unwilling participant in medical experiments that involved injection of 4.7 micrograms of Plutonium on 10 April 1945 at Oak Ridge, Tennessee. This experiment was under the supervision of Harold Hodge. 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. The government covered up most of these radiation mishaps 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.


Applications


Explosives

The isotope plutonium-239 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 (an optional layer of dense material) decreases the amount of plutonium needed to reach critical mass (nuclear), critical mass by neutron reflector, reflecting escaping neutrons back into the plutonium core. This reduces the amount of plutonium needed to reach criticality from 16 kg to 10 kg, which is a sphere with a diameter of about . This critical mass is about a third of that for uranium-235. The Fat Man plutonium bombs used explosive compression of plutonium to obtain significantly higher densities than normal, combined with a central neutron source to begin the reaction and increase efficiency. Thus only 6.2 kg of plutonium was needed for an nuclear weapon yield, explosive yield equivalent to 20 kilotons of TNT. Hypothetically, as little as 4 kg of plutonium—and maybe even less—could be used to make a single atomic bomb using very sophisticated assembly designs.


Mixed oxide fuel

Spent nuclear fuel from normal light water reactors 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. 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 reactors. 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. 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 reactors and consists of 60 kg of plutonium per tonne of fuel; after four years, three-quarters of the plutonium is burned (turned into other elements). Breeder reactors are specifically designed to create more fissionable material than they consume. MOX fuel has been in use since the 1980s, and is widely used in Europe. In September 2000, the United States and the Russian Federation signed a Plutonium Management and Disposition Agreement by which each agreed to dispose of 34 tonnes of weapons-grade plutonium. The U.S. Department of Energy plans to dispose of 34 tonnes of weapons-grade plutonium in the United States before the end of 2019 by converting the plutonium to a MOX fuel to be used in commercial nuclear power reactors. 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. Any uranium or plutonium isotopes produced during those three years are left and the rod goes back into production. 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. 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. 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. 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".


Power and heat source

The isotope plutonium-238 has a half-life of 87.74 years. It emits a large amount of thermal energy with low levels of both gamma rays/photons and spontaneous neutron rays/particles. 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 emitted by plutonium-238. One kilogram of the isotope can generate about 570 watts of heat. 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 A radioisotope thermoelectric generator (RTG, RITEG) is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive Radioactive decay (also known as nuclear decay, radi ...
s and radioisotope heater units such as those in the Cassini–Huygens, Cassini, Voyager program, Voyager, Galileo (spacecraft), Galileo and New Horizons space probes, and the Curiosity (rover), Curiosity and Perseverance (rover), Perseverance (Mars 2020) Mars rovers. The twin Voyager spacecraft were launched in 1977, each containing a 500 watt plutonium power source. Over 30 years later, each source is still producing about 300 watts which allows limited operation of each spacecraft. An earlier version of the same technology powered five ALSEP, Apollo Lunar Surface Experiment Packages, starting with Apollo 12 in 1969. Plutonium-238 has also been used successfully to power artificial heart artificial pacemaker, pacemakers, to reduce the risk of repeated surgery. It has been largely replaced by lithium-based primary cells, but there were somewhere between 50 and 100 plutonium-powered pacemakers still implanted and functioning in living patients in the United States. By the end of 2007, the number of plutonium-powered pacemakers was reported to be down to just nine. Plutonium-238 was studied as a way to provide supplemental heat to scuba diving. Plutonium-238 mixed with beryllium is used to generate neutrons for research purposes.


Precautions


Toxicity

There are two aspects to the harmful effects of plutonium: the radioactivity and the Heavy metal (chemistry)#Detrimental effects, heavy metal poison effects. Isotopes and compounds of plutonium 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. 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. During the decay of plutonium, three types of ionizing radiation are released, namely alpha, beta, and gamma. 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. Alpha radiation can travel only a short distance and cannot travel through the outer, dead layer of human skin. Beta radiation can penetrate human skin, but cannot go all the way through the body. Gamma radiation can go all the way through the body. Even though alpha radiation cannot penetrate the skin, ingested or inhaled plutonium does irradiate internal organs. Alpha particles generated by inhaled plutonium have been found to cause lung cancer in a cohort of European nuclear workers. The skeleton, where plutonium accumulates, and the liver, where it collects and becomes concentrated, are at risk. Plutonium is not absorbed into the body efficiently when ingested; only 0.04% of plutonium oxide is absorbed after ingestion. Plutonium absorbed by the body is excreted very slowly, with a biological half-life of 200 years. Plutonium passes only slowly through cell membranes and intestinal boundaries, so absorption by ingestion and incorporation into bone structure proceeds very slowly. 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. Plutonium is more dangerous when inhaled than when ingested. The risk of lung cancer increases once the total radiation equivalent dose, dose equivalent of inhaled plutonium exceeds 400 sievert, mSv. The U.S. Department of Energy estimates that the lifetime cancer risk from inhaling 5,000 plutonium particles, each about 3 µm wide, is 1% over the background U.S. average. 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. 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. 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. A commonly cited quote by Ralph Nader states that a pound of plutonium dust spread into the atmosphere would be enough to kill 8 billion people. 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 million people by inhalation, so that the toxicity of plutonium is roughly equivalent with that of nerve gas. (Online version of Cohen's book ''The Nuclear Energy Option'' (Plenum Press, 1990) ). 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. "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."


Marine toxicity

Investigating the toxicity of plutonium in humans is just as important as looking at the effects in fauna of marine systems. Plutonium is known to enter the marine environment by dumping of waste or accidental leakage from nuclear plants. Although the highest concentrations of plutonium in marine environments are found in the sediments, the complex biogeochemical cycle of plutonium means that it is also found in all other compartments. 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. 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 geographical distribution around the globe. One study investigated the effects of transuranium elements (plutonium-238,
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but differe ...

plutonium-239
, plutonium-240) on various fish living in the 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. Similar studies found large accumulations of plutonium in the respiratory and digestive organs of cod, flounder and herring. 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. The Oak Ridge National Laboratory displayed that carp and minnow embryos raised in solutions containing plutonium isotopes did not hatch; eggs that hatched displayed significant abnormalities when compared to control developed embryos. It revealed that higher concentrations of plutonium have been found to cause issues in marine fauna exposed to the element.


Criticality potential

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. A critical mass of plutonium emits lethal amounts of neutrons and gamma rays. 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. Criticality accidents have occurred in the past, some of them with lethal consequences. Careless handling of tungsten carbide bricks around a 6.2 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 to be 5.1 sievert (510 Roentgen equivalent man, rems) and died 25 days later. Nine months later, another Los Alamos scientist, Louis Slotin, died from a similar accident involving a beryllium reflector and the same plutonium core (the so-called "demon core") that had previously claimed the life of Daghlian. In December 1958, during a process of purifying plutonium at Los Alamos, a critical mass was formed in a mixing vessel, which resulted in the death of a chemical operator named Cecil Kelley criticality accident, Cecil Kelley. Other nuclear and radiation accidents, nuclear accidents have occurred in the Soviet Union, Japan, the United States, and many other countries.


Flammability

Metallic plutonium is a fire hazard, especially if the material is 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. The radioactivity of the burning material is an additional 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.


Transportation


Land and sea

The usual transportation 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 kg of plutonium oxide. A sea shipment may consist of several containers, each of them holding a sealed package. The United States Nuclear Regulatory Commission dictates that it must be solid instead of powder if the contents surpass 0.74 Becquerel, TBq (20 Curie (unit), Curies) of radioactive activity. In 2016, the ships MV Pacific Egret, ''Pacific Egret'' and ''Pacific Heron'' of Pacific Nuclear Transport Ltd. transported 331 kg (730 lbs) of plutonium to a United States government facility in Savannah River Site, Savannah River, South Carolina.


Air

The 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. In 2012 media revealed that plutonium has been flown out of Norway on commercial passenger airlines—around every other year—including one time in 2011. Regulations permit an airplane to transport 15 grams of fissionable material. Such plutonium transportation is without problems, according to a senior advisor (''seniorrådgiver'') at Statens strålevern.


Notes


Footnotes


Citations


References

* * * * * * * * * * * * * * * * * * * * * * * * * * *


External links

* * * * * * * * * * * * {{featured article Plutonium, Chemical elements Actinides Carcinogens Nuclear materials Synthetic elements Manhattan Project Materials that expand upon freezing