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Plutonium is a radioactive, metallic, man made chemical element. In the periodic table it has the symbol Pu and the atomic number 94. Its atomic weight is 244.06, its density 19,800 kg/m3.

Plutonium was discovered in 1941 by Dr. Glenn T. Seaborg and others working at the University of California, Berkeley; the discovery was kept secret. It was named after the planet Pluto, having been discovered directly after Neptunium. (Pluto is the next planet out after Neptune).

The most important isotope of plutonium is 239Pu, with a half-life of 24,200 years. Because of its low half-life, there are only extremely tiny trace amounts of plutonium naturally.

Plutonium is the key fissile component in modern nuclear weapons, and it could also be used to manufacture radiological weapons or as a (not particularly deadly) poison. Large stockpiles of plutonium were accumulated by both NATO and the Warsaw Pact, which since the end of the cold war have become a focus of nuclear proliferation concerns. In 2002, the United States Department of Energy took possession of 34 metric tons of excess weapons grade plutonium stockpiles from the United States Department of Defense, and as of early 2003 was considering converting several nuclear power plants in the US from enriched uranium fuel[?] to MOX fuel as a means of disposing of these.


Plutonium is sometimes referred in media reports to as the most toxic substance known to man, although there is general agreement among experts in the field that this is overstated. As of 2003, there has yet to be a single human death officially attributed to plutonium exposure, naturally-occurring radium is about 200 times more radiotoxic than plutonium, and some organic toxins like Botulism toxin are billions of times more toxic than plutonium.

The chemical and radiological toxicity of plutonium should be distinguished from the danger of plutonium. Many, both in the anti-nuclear movement[?] and in the continuing green politics movement, refer to plutonium as the most dangerous substance known to man because of its crucial role in the production of nuclear weapons.

Possibly it is confusing these two issues that has led to sensational exaggerations[?] of plutonium toxicity. A 1989 paper by Bernard L. Cohen[?] states, "Pu hazards are far better understood than [those from insecticides or food additives], and the one fatality per 300 years they may someday cause is truly trivial by comparison. In spite of the facts we have cited here, facts well known in the scientific community, the myth of Pu toxicity lingers on." [1] (http://www.environmental.usace.army.mil/info/technical/hp/hpfaq/THE_MYTH_OF_PLUTONIUM_TOXICITY.doc) (html-ized version (http://russp.org/BLC-3))

That said, there is no doubt that plutonium is extremely dangerous. It is an alpha emitter, and this radiation does not penetrate the skin. The danger with all alpha emitters is rather if they are inhaled or otherwise ingested. Extremely small particles of plutonium on the order of micrograms can cause lung cancer if inhaled into the lungs. Slightly larger amounts will cause acute radiation poisoning and death if ingested or inhaled.

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See: Periodic Table

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