plutonium (Pu)

plutonium's location in the periodic table

Plutonium (Pu) is a radioactive, silvery, metallic element, occurring in uranium ores and produced artificially by neutron bombardment of uranium. Plutonium has 15 isotopes with masses ranging from 232 to 246 and half-lives from 20 minutes to 76 million years. Plutonium is a radiological poison, specifically absorbed by bone marrow, and is used, especially the highly fissionable isotope plutonium-239, as a nuclear fuel.


Plutonium was discovered in 1940 by the American researchers Seaborg, McMillan, Wahl, and Kennedy as the second transuranium element upon bombardment of uranium-238 with deuterons, thus forming Pu-238. The elements 93 and 94 following the 92nd element – uranium – in the classification of elements have been named analogously to uranium, which is named after the planet Uranus, 'neptunium' and 'plutonium', the planets Neptune and Pluto following Uranus.


atomic number 94
relative density 19.4
melting point 639.5°C (1,183°F)
boiling point 3,227°C (5,841°F)



Due to its property as fissile material, the isotope Pu-239 (half-life 24,110 years) is of specific importance. It is generated by neutron capture in uranium-238 and two subsequent beta decays according to the following scheme:


U-238 + n → U-239 → β-decay → Np-239 → β-decay → Pu-239.


In nature, plutonium-239 occurs in tiny quantities in minerals containing uranium (pitchblende, carnotite) – one plutonium atom per 1 trillion and more uranium atoms. It is formed from U-238 by neutron capture released upon the spontaneous fission of U-238. In above-ground nuclear weapon tests, approximately six tonnes of Pu-239 were released into the atmosphere and distributed all over the world, so that in Central Europe for example, about 60 Bq Pu-239 per m2 have been deposited.


Plutonium is a radiotoxic substance and its chemical toxicity as a heavy metal is therefore negligible. The radiotoxic effect of plutonium is very serious in the case of inhalation of the finest plutonium aerosols; ingestion of plutonium is about 10,000 times less dangerous, since only 1/100 percent of plutonium is absorbed by the intestinal mucosa, 99.99% is excreted immediately.