94 neptuniumplutoniumamericium


Name, Symbol, Number plutonium, Pu, 94
Chemical series actinides
Group, Period, Block n/a, 7, f
Appearance silvery white
Gloved hands holding a "button" of refined plutonium
Atomic mass (244) g/mol
Electron configuration [Rn] 5f6 7s2
Physical properties
Phase solid
Density (near r.t.) 19.816 g/cm³
Liquid density at m.p. 16.63 g/cm³
Melting point 912.5 K
(639.4 °C, 1182.9 °F)
Boiling point 3505 K
(3228 °C, 5842 °F)
Heat of fusion 2.82 kJ/mol
Heat of vaporization 333.5 kJ/mol
Heat capacity (25 °C) 35.5 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1756 1953 2198 2511 2926 3499
Atomic properties
Crystal structure monoclinic
Oxidation states 6, 5, 4, 3
(amphoteric oxide)
Electronegativity 1.28 (Pauling scale)
Ionization energies 1st: 584.7 kJ/mol
Atomic radius 175 pm
Magnetic ordering no data
Electrical resistivity (0 °C) 1.460 µΩ·m
Thermal conductivity (300 K) 6.74 W/(m·K)
Thermal expansion (25 °C) 46.7 µm/(m·K)
Speed of sound (thin rod) (r.t.) 96 m/s
Shear modulus 43 GPa
Poisson ratio 0.21
CAS registry number 7440-07-5
Notable isotopes
Main article: Isotopes of plutonium
iso NA half-life DM DE (MeV) DP
238Pu syn 88 y SF - -
α 5.5 234U
239Pu syn 2.41×104 y SF - -
α 5.245 235U
240Pu syn 6.5×103 y SF - -
β 0.005 240Am
241Pu syn 14 y β - 241Am
SF - -
242Pu syn 3.73×105 y SF - -
α 4.984 238U
244Pu trace 8.08×107 y α 4.666 240U
SF - -

Plutonium (chemical symbol Pu, atomic number 94) is a radioactive, metallic chemical element that is part of the actinide series. It is the element used in most modern nuclear weapons. The most important isotope of plutonium is 239Pu, with a half-life of 24,110 years. It can be made from natural uranium and is fissile, meaning it can readily break apart to become lighter elements. The most stable isotope is 244Pu, with a half-life of about 80 million years, long enough to be found in extremely small quantities in nature. In fact, 244Pu is the heaviest atom naturally occurring in traces in the Earth's crust.






A 5.3-kilogram ring of weapons-grade, electrorefined plutonium, at 99.96 percent purity. This amount of plutonium is sufficient for use in a modern nuclear weapon.







The production of plutonium and neptunium by bombarding uranium-238 with neutrons was predicted in 1940 by two teams working independently: Edwin M. McMillan and Philip Abelson at Berkeley Radiation Laboratory at the University of Berkeley, California and by Egon Bretscher and Norman Feather at the Cavendish Laboratory at University of Cambridge. Coincidentally both teams proposed the same names to follow on from uranium, like the sequence of the outer planets.



During the Manhattan Project, the first production reactor was built at the Oak Ridge, Tennessee, site that later became Oak Ridge National Laboratory. Later, large reactors were set up in Hanford, Washington, for the production of plutonium, which was used in the first atomic bomb used at the "Trinity" test at White Sands, New Mexico in July 1945. Plutonium was also used in the "Fat Man" bomb dropped on Nagasaki, Japan in August 1945. The "Little Boy" bomb dropped on Hiroshima utilized uranium-235, not plutonium.

Large stockpiles of plutonium were built up by both the Soviet Union and the United States during the Cold War—it was estimated that 300,000 kg of plutonium had been accumulated by 1982. Since the end of the Cold War, these stockpiles have become a focus of nuclear proliferation concerns. In 2002, the U.S. Department of Energy took possession of 34 metric tons of excess weapons-grade plutonium stockpiles from the U.S. Department of Defense, and, as of early 2003, was considering converting several nuclear power plants in the United States from enriched uranium fuel to MOX fuel[4] as a means of disposing of plutonium stocks.




Notable characteristics

Plutonium is an inner transition metal of the actinide series, located in period 7 of the periodic table, between neptunium and americium. It has been called "the most complex metal" and "a physicist's dream but an engineer's nightmare"[7] for its peculiar physical and chemical properties.

It has six allotropes normally and a seventh under pressure, all of which have very similar energy levels but with significantly varying densities, making it very sensitive to changes in temperature, pressure, or chemistry, and allowing for dramatic volume changes following phase transitions (in nuclear applications, it is usually alloyed with small amounts of gallium, which stabilizes it in the delta-phase.)[8] Plutonium is silvery in pure form, but has a yellow tarnish when oxidized. It is also notable in that it possesses a low-symmetry structure causing it to become progressively more brittle over time.[9] Because it self-irradiates, it ages both from the outside-in and the inside-out.[8] However, self-irradiation can also lead to annealing, which counteracts some of the aging effects. In general, the precise aging properties of plutonium are very complex and poorly understood, greatly complicating efforts to predict future reliability of weapons components.

The heat given off by alpha particle emission makes plutonium warm to the touch in reasonable quantities. In aqueous solution, it displays five ionic oxidation states:

  • PuIII, as Pu3+ (blue lavender)
  • PuIV, as Pu4+ (yellow brown)
  • PuVI, as PuO22+ (pink orange)



A diagram of the allotropes of plutonium at ambient pressure














  • PuO2(CO3)1-2
  • PuO2(CO3)2-4
  • PuO2(CO3)3-6



The isotope 239Pu is a key fissile component in nuclear weapons, due to its ease of fissioning and availability. The critical mass for a sphere of plutonium without a tamper reflector[12] is 16 kg, but through the use of a neutron-reflecting tamper the pit of plutonium in a fission bomb is reduced to 10 kg, which is a sphere with a diameter of 10 cm.

The Manhattan Project "Fat Man" type plutonium bombs, using explosive compression of Pu to significantly higher densities than normal, were able to function with plutonium cores of only 6.2 kg.[13] Complete detonation of plutonium will produce an explosion equivalent to the explosion of 20 kilotons of trinitrotoluene (TNT) per kilogram. However, complete detonation requires an additional neutron source (often from a small amount of fusion fuel), and primitive bombs may be far less efficient. For example, despite the 6.2 kg of plutonium, the Fat Man yield was only 21 kt.

Plutonium could also be used to manufacture radiological weapons or as a radiologic poison. In a number of instances damaged nuclear weapons have spread plutonium over a surrounding area, similar to the effect of a so-called "dirty bomb," and required extensive cleanup. On the other hand, 5 kg of plutonium was spread over the Nagasaki area (due to incomplete fission) and never cleaned up. The toxicity of plutonium is in dispute; nuclear industry advocates point to the low chemical toxicity of plutonium and ability of a worker to hold a kilogram brick of the material without protection; if inhaled or digested, however, plutonium's effects due to radioactivity overwhelm the effects of plutonium's chemical interactions with the body, and the LD50 dose for intravenous injection in an adult human weighing 70 kilograms is calculated to be approximately 22 milligrams (based on extrapolation from tests on dogs).[14] The insistence on both sides of the issue of plutonium's safety/deadliness casts questions on the current habitability of areas that have been exposed to nuclear warfare and on the health of the current residents.


238Pu has been used successfully to power artificial heart pacemakers, to reduce the risk of repeated surgery. It has been largely replaced by Lithium based primary cells, but as of 2003 there were somewhere between 50 and 100 plutonium-powered pacemakers still implanted and functioning in living patients.



All isotopes and compounds of plutonium are toxic and radioactive. Although media reports occasionally describe plutonium as "the most toxic substance known to man," from the standpoint of literal toxicity this is incorrect. As of 2006, there has yet to be a single human death officially attributed to exposure to plutonium itself (with the exception of plutonium-related criticality accidents). Naturally occurring radium is about 200 times more radiotoxic than plutonium, and some organic toxins like botulin toxin are still more toxic. Botulin toxin, in particular, has a lethal dose of 300 pg per kg of body weight, far less than the quantity of plutonium that poses a significant cancer risk. In addition, beta and gamma emitters (including the carbon-14 and potassium-40 in nearly all food) can cause cancer on casual contact, which alpha emitters cannot.




Other substances—-including ricin, tetrodotoxin, botulinum toxin, and tetanus toxin-—are fatal in doses of (sometimes far) under one milligram, and others (the nerve agents, the amanita toxin) are in the range of a few milligrams. As such, plutonium is not unusual in terms of toxicity, even by inhalation. In addition, those substances are fatal in hours to days, whereas plutonium (and other cancer-causing radioactive agents) give an increased chance of illness decades in the future. Considerably larger amounts may cause acute radiation poisoning and death if ingested or inhaled. So far, however, no human is known to have died immediately died after inhaling or ingesting plutonium, and many people have measurable amounts of plutonium in their bodies.

Disposal difficulties


Criticality potential





See also


  1. As one article puts it, referring to information Seaborg gave in a talk: "The obvious choice for the symbol would have been Pl, but facetiously, Seaborg suggested Pu, like the words a child would exclaim, 'Pee-yoo!' when smelling something bad. Seaborg thought that he would receive a great deal of flak over that suggestion, but the naming committee accepted the symbol without a word." David L. Clark and David E. Hobart, "Reflections on the Legacy of a Legend: Glenn T. Seaborg, 1912-1999," Los Alamos Science 26 (2000): 56-61, on 57. Retrieved March 20, 2007.
  2. Frontline interview with Seaborg "Nuclear Reaction: Why do American Fear Nuclear Power?" PBS. Retrieved March 20, 2007.
  3. National Historic Landmarks Program: Room 405, George Herbert Jones Laboratory National Park Service. Retrieved March 20, 2007.
  5. William Moss and Roger Eckhardt, "The Human Plutonium Injection Experiments," Los Alamos Science (1995). Retrieved March 20, 2007.
  6. Michael S. Yesley, "'Ethical Harm' and the Plutonium Injection Experiments," Los Alamos Science 23 (1995): 280-283, on 283. Retrieved March 26, 2015.
  7. "Plutonium: An element at odds with itself," Los Alamos Science 26 (2000): 16. Retrieved March 20, 2007.
  8. 8.0 8.1 Siegfried S. Hecker, "Plutonium and Its Alloys: From atoms to microstructure," Los Alamos Science 26 (2000): 290-335. Retrieved March 20, 2007.
  9. Anne Stark, 2006. "Scientists tackle long-standing questions about plutonium" Lawrence Livermore National Laboratory. Retrieved March 26, 2015.
  10. William J. Crooks III, Nuclear Criticality Safety Engineering Training Module 10 - Criticality Safety in Material Processing Operations, Part 1 U.S. Department of Energy, Nuclear Criticality Safety Program. Retrieved March 20, 2007.
  11. George Matlack. A Plutonium Primer: An Introduction to Plutonium Chemistry and its Radioactivity. (LA-UR-02-6594)
  12. A tamper is an optional layer of dense material (typically natural or depleted uranium or tungsten) surrounding the fissile material. It reduces the critical mass and increases the efficiency by its inertia which delays the expansion of the reacting material.
  13. Much of the information about plutonium in the Fat Man bomb comes from reports of the criticality accidents of Harry K. Daghlian, Jr. and Louis Slotin, both of whom died after conducting experiments with plutonium bomb cores. See, for instance, Los Alamos and the Omega Site Accident. Retrieved March 20, 2007.
  14. George L. Voelz and Ileana G. Buican, Plutonium and Health: How Great is the Risk? Los Alamos Science 26 (2000). Retrieved March 26, 2015.
  15. National Academy of Sciences, Committee on International Security and Arms Control, Management and Disposition of Excess Weapons Plutonium (National Academy Press, 1994). Retrieved March 20, 2007.
  16. David Albright and Kevin O'Neill, "The Lessons of Nuclear Secrecy at Rocky Flats" U.S. Dept. of Energy Communication. Retrieved March 26, 2015.
  17. Plutonium ISIS Issue Brief. Retrieved March 26, 2015.


  • Emsley, John. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford University Press, 2001. ISBN 0198503407.
  • Greenwood, N.N., and A. Earnshaw. Chemistry of the Elements, 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann, 1998. ISBN 0750633654. Online version.
  • Hampel, Clifford A. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp., 1968. ISBN 0442155980.
  • Morss, Lester R., Norman M. Edelstein, and Jean Fuger (eds.). The Chemistry of the Actinide and Transactinide Elements, 3rd ed. 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer, 2006. ISBN 1402035551.
  • Stwertka, Albert. Guide to the Elements, Rev. ed. Oxford: Oxford University Press, 1998. ISBN 0195080831.

External links

All links retrieved March 29, 2019.

Nuclear technology



