Plutonium is a chemical element with the atomic number 94 in the periodic table. Despite being a synthetically produced substance, some trace amounts of plutonium may occur naturally in combination with other chemical elements. This chemical is discovered as the second synthetic transuranium element of the actinide series of the periodic table.
Being a member of the actinides family of periodic table elements, this highly radioactive transuranic metallic element is a divalent substance. Along with uranium-235, plutonium-239 is one of the two fissile materials that are popularly used in the construction of nuclear weapons and atomic bombs, as well as for the production of energy in nuclear power plants.
Any exposure to any form and quantity of plutonium’s radioactivity is extremely dangerous to human health, all living organisms, and environmental systems.
Chemical and Physical Properties of Plutonium
The symbol in the periodic table of elements: Pu
Atomic number: 94
Atomic weight (mass): (244) g.mol-1
Group number: Actinides
Period: 7 (f-block)
Color: A silvery-white radioactive metal
Physical state: Solid at room temperature
Half-life: From 1.1(+20−5) seconds to 80.8 million years
Electronegativity according to Pauling: Unknown
Density: 19.84 g.cm-3 at 20°C
Melting point: 640°C, 1184°F, 913 K
Boiling point: 3228°C, 5842°F, 3501 K
Van der Waals radius: Unknown
Ionic radius: Unknown
Most characteristic isotope: 238Pu, 239Pu, 240Pu
Electronic shell: [Rn] 5f6 7s2
The energy of the first ionization: 558.6 kJ.mol-1
The energy of the second ionization: N/A
Discovery date: In 1940-1941 by Glenn Seaborg and colleagues
With the periodic table symbol Pu, atomic number 94, atomic mass of (244) g.mol-1, and electron configuration [Rn] 5f6 7s2, plutonium is a synthetically produced silvery-white radioactive metal. It reaches its boiling point at 3228°C, 5842°F, 3501 K, while the melting point is reached at 640°C, 1184°F, 913 K.
Having an atomic number greater than 92, this man-made radioactive substance belongs to the class of transuranium elements. Unlike other chemical elements, the density of plutonium increases when it’s exposed to high temperatures. In addition, the electronegativity according to Pauling of this member of the actinides family of elements is unknown, as well as the atomic radius according to van der Waals.
Plutonium occurs in several allotropes which differ in their crystal structure and density. Normally, there are typically six plutonium allotropes. When exposed to high temperatures, plutonium forms a seventh (zeta, ζ) allotrope which is widely different from all other forms of this chemical element.
This chemical element has a monoclinic crystal structure and possesses strong paramagnetic properties, but has poor thermal and electrical conductivity. When exposed to air, plutonium metal oxidizes with dull gray, yellow, or olive green tarnish.
How Was Plutonium Discovered?
Plutonium was discovered in 1940 by an American team of renewed scientists which included Edwin M. McMillan, J. W. Kennedy, and A. C. Wahl. Led by Dr. Glenn T. Seaborg (1912–1999). The team of discoverers performed their revolutionary experiment at the University of California, Berkeley in the later part of 1940.
The story of plutonium’s discovery begins in 1939, after the announcement of the nuclear fission phenomenon by the scientists Otto Hahn and Fritz Strassmann. A year later, the American physicist and Nobel laureate Edwin M. McMillan (1907 – 1991) confirmed this phenomenon in a joint effort with the American physicist, scientific editor, and science writer Philip Abelson (1913 – 2004).
By using the small 27-inch cyclotron at Berkeley laboratory, McMillan and Abelson bombarded uranium-238 isotopes with neutrons produced from deuterons. This chemical reaction produced a decay chain in which the resulting uranium-238 decayed to neptunium-238, which underwent a beta decay to form plutonium (94Pu). Unfortunately, McMillan wasn’t able to finish the experiment and prove that it’s fissionable because WWII was raging, and he was asked to help with the production of nuclear bombs at the Los Alamos National Laboratory, United States.
At that point, Dr. Seaborg and his colleagues took over and continued with McMillan’s project. Shortly after they commenced where McMillan had stopped, the team of scientists observed that slow neutrons cause plutonium-239 to undergo fission, continuing the nuclear chain reaction by releasing more and more neutrons. This revolutionary discovery meant that plutonium can be used as a new material from which a nuclear bomb could be constructed.
The first visible quantity of plutonium [a microgram of pure plutonium-239 compound (plutonium IV iodate)] was synthetically produced in 1942 by Burris Cunningham and Louis Werner at the Metallurgical Laboratory of the University of Chicago.
In 1943, the first sample of plutonium metal was produced by reducing plutonium trifluoride with lithium.
The Manhattan Project
After the team of researchers discovered plutonium and observed it could sustain a nuclear chain reaction, Seaborg secretly wrote to President Roosevelt, informing him about this new substance that possesses the potential to be a powerful source of nuclear energy.
Realizing the advantage of this substance as a nuclear weapon in the war, a secret project codenamed the Manhattan Engineering District was established. The aim of the Manhattan Project was to produce a nuclear bomb.
How Did Plutonium Get Its Name?
Element 94 was named after the planet Pluto. The naming of the new chemical element plutonium after a planet continues the pattern started by Martin Klaproth, who named the element uranium after the planet Uranus.
Where Can You Find Plutonium?
Plutonium is a byproduct of the nuclear power industry made in various types of nuclear reactors. However, trace quantities of plutonium may occur in nature, mostly combined with other elements. Also, some plutonium quantities can be found in natural uranium ores.
Most of this highly radioactive chemical element is commercially produced in power reactors used for research or plutonium production reactors. The latter ones are also called breeder reactors because they produce more plutonium than they consume fuel.
Plutonium in Everyday Life
In addition to being used as the main source of energy in nuclear reactors and weapons, this transuranic element has some practical everyday uses as well:
- The first heart pacemakers used to be made with plutonium-238 as the power source.
- Plutonium is used for the production of nuclear bombs, which are the most powerful weapons in the world. The iconic image of the mushroom cloud after the explosion signifies the extreme power released by a nuclear bomb.
- Plutonium-238 is applied as a heat source by using radioisotope thermoelectric generators (RTGs) to produce electricity in devices such as unmanned spacecraft and interplanetary space probes. Some probes that use plutonium-238 are Cassini and Galileo.
- Plutonium-239 is one of the main radioisotopes applied in the construction of nuclear weapons. Namely, this plutonium form is the weapons-grade fissile isotope used in nuclear bombs, ie. nukes. The amount of plutonium used in fission weapons ranges from 3 to 5 kilograms.
- Thorium-plutonium-uranium alloys are studied as a possible nuclear fuel for the fast breeder reactors, while the plutonium-gallium–cobalt alloy (PuCoGa5) is observed as an unconventional superconductor;
- This man-made radioactive substance is also the main fuel in fast neutron reactors.
How Dangerous Is Plutonium?
According to The Department of Health and Human Services (DHHS), the International Agency for Research on Cancer (IARC), the U.S. Department of Energy, and the EPA’s Office of Air and Radiation, plutonium is a highly radioactive substance and a powerful carcinogen.
Exposure to this chemical element may lead to severe health problems. Due to the fact that plutonium emits alpha particles, this substance is especially dangerous if inhaled. It also emits neutrons, beta particles, and gamma rays. When plutonium enters the body, its radioactive particles protrude all tissues and destroy the cells, which results in severe forms of cancer and death. For more information about possible countermeasures for internal contamination with plutonium, please see CDC’s fact sheet.
Environmental Effects of Plutonium
The trace amount of plutonium that naturally occurs does not pose any environmental threat. However, the atmospheric testing of nuclear bombs, weapons testing, plutonium release from research facilities, nuclear waste disposal, radioactive plutonium emissions from the nuclear fuel reprocessing facilities, and nuclear weapons production facilities present some of the biggest environmental concerns of our time.
When released uncontrollably, plutonium may saturate the air, contaminate the soil and surface waters, or fall as a contaminated precipitate. In this way, plutonium undergoes a radioactive decay chain in the environment which is extremely dangerous for all life forms in all environmental systems.
Isotopes of Plutonium
There are 20 isotopes of plutonium produced so far. All of them are radioactive and are involved in a decay chain that produces new isotopes of the elements U, Np, Pb, Mg, Si, Cm, and Am. Alpha decay is the most common form of radioactive decay for element 94. While some radionuclides have half-lives of mere seconds, others live up to several millions of years.
Plutonium-244 is the most stable isotope of this chemical element, while plutonium-238 and plutonium-239 are the most common forms of plutonium. Due to the spontaneous fission (10 fission/s-kg), plutonium-239 isotope has a reasonably low rate of neutron emission. On the other hand, plutonium-240 has a relatively high spontaneous fission rate.
In general, plutonium isotopes have an amazingly long half-life:
- Plutonium-244 (a half-life of 80.8 million years);
- Plutonium-242 (a half-life of 373.300 years);
- Plutonium-239 (a half-life of 24.110 years);
- Plutonium-238 (a half-life of s 87.7 years).
|Z||N||Isotopic mass (Da)
[n 2][n 3]
[n 5][n 6]
[n 7][n 8]
|228Pu||94||134||228.03874(3)||1.1(+20−5) s||α (99.9%)||224U||0+|
|232Pu||94||138||232.041187(19)||33.7(5) min||EC (89%)||232Np||0+|
|233Pu||94||139||233.04300(5)||20.9(4) min||β+ (99.88%)||233Np||5/2+#|
|234Pu||94||140||234.043317(7)||8.8(1) h||EC (94%)||234Np||0+|
|235Pu||94||141||235.045286(22)||25.3(5) min||β+ (99.99%)||235Np||(5/2+)|
|238Pu||94||144||238.0495599(20)||87.7(1) y||α||234U||0+||Trace[n 9]|
|239Pu[n 10][n 11]||94||145||239.0521634(20)||2.411(3)×104 y||α||235U||1/2+||Trace[n 12]|
|240Pu||94||146||240.0538135(20)||6.561(7)×103 y||α||236U||0+||Trace[n 13]|
|241Pu[n 10]||94||147||241.0568515(20)||14.290(6) y||β− (99.99%)||241Am||5/2+|
|243Pu[n 10]||94||149||243.062003(3)||4.956(3) h||β−||243Am||7/2+|
|244Pu||94||150||244.064204(5)||8.00(9)×107 y||α (99.88%)||240U||0+||Trace[n 14]|
List of Plutonium Compounds
Plutonium is a chemical element that is extremely sensitive to changes in temperature and chemical composition. It readily dissolves in perchloric acid, hydroiodic acid, as well as in a solution of hydrogen chloride (hydrochloric acid).
As a part of a compound, plutonium occurs in the 0 oxidation state (metallic form), and +3, +4, +5, +6, +7 oxidation states in molecular systems.
- MOX fuel
- Plutonium borides
- Plutonium carbide
- Plutonium hexafluoride
- Plutonium hydride
- Plutonium tetrafluoride
- Plutonium–gallium alloy
- Plutonium(III) bromide
- Plutonium(III) chloride
- Plutonium(III) fluoride
- Plutonium(IV) oxide
5 Interesting Facts and Explanations
- Nuclear weapons made with plutonium are the most devastating in the world. As an illustration of this claim, the plutonium bomb labeled as “Fat Man” dropped in Nagasaki, Japan on August 9, 1945, was enough to destroy the entire city.
- Dr. Glenn Seaborg was also invited to participate with his knowledge and practical experience in the Manhattan Project and the former U.S. Atomic Energy Commission.
- At the U.S. Atomic Energy Commission (AEC), Seaborg was investing his knowledge and scientific credibility as a scientist for arms control and management of the highly destructive atomic power produced by his work.
- In 1951, Edwin Mattison McMillan and Dr. Glenn Seaborg shared the Nobel prize in Chemistry for being the first scientists to produce the first-ever transuranium element, neptunium.
- Until plutonium was discovered, only uranium-235 isotopes were used for the production of nuclear bombs.