Plutonium was discovered in 1941 by Dr. Glenn T. Seaborg and Edwin McMillan, Kennedy, and Wahl by deuteron bombardment of Uranium in the 60-inch cyclotron of the Berkeley Radiation Laboratory at the University of California, Berkeley, but 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 metal has a silvery appearance and takes on a yellow tarnish when slightly oxidized. It is chemically reactive. A relatively large piece of Plutonium is warm to the touch because of the energy given off in alpha decay. Larger pieces will produce enough heat to boil water. The metal readily dissolves in concentrated hydrochloric acid, hydroiodic acid, or perchloric acid. The metal exhibits six allotropic modifications having various crystalline structures. The densities of these vary from 16.00 to 19.86 g/cm3.
The most important isotope
of Plutonium is 239Pu, with a half-life
of 24,200 years. Because of its short half-life, there are only
extremely tiny trace amounts of Plutonium naturally in Uranium
Plutonium could also be used to manufacture radiological weapons. The Plutonium
isotope 238Pu is an alpha emitter with a half life of 87 years. These
characteristics make it well suited for electrical power generation for devices
which must function without direct maintenance for timescales approximating a
human life time. It is therefore used in RTGs such as those powering the Galileo
and Cassini space probes. Plutonium-238 was used on the Apollo-14 lunar flight
in 1971 to power seismic devices and other equipment left on the Moon, and it
was also the power supply of the two Voyager supercraft launched in 1977.
Plutonium-239 can also be used as a fuel in a new generation of fast-breeder nuclear weapons, which burn a mixed oxide (MOX) fuel consisting of Uranium and Plutonium.
Plutonium in the environment
Trace amounts of Plutonium are found
naturally in Uranium-rich ores. Humans produce most of the
existing Plutonium, in special nuclear reactors. Besides being
naturally present in very small amounts, Plutonium may also enter
the environment from releases of nuclear reactors, weapons
production plants, and research facilities. A major source of
Plutonium release is nuclear weapons testing.
Plutonium is sometimes
described in media reports as the most toxic substance known to man, although
there is general agreement among experts in the field that this is incorrect. 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.
Plutonium may enter surface water from accidental releases and disposal of radioactive wastes. Soil can become contaminated with Plutonium through fallout during nuclear weapons testing. Plutonium moves slowly downwards in the soil, into the groundwater.
Plants absorb low levels of Plutonium, but these levels are not high enough to cause bio magnification of Plutonium up the food chain, or accumulation in the bodies of animals.