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Jai Ganesh

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Plutonium

Plutonium

Gist

Plutonium (Pu, atomic number 94) is a radioactive, heavy, actinide metal known for its use in nuclear weapons and nuclear batteries, and for being a product of nuclear fission in nuclear reactors. It is chemically toxic and poses significant health risks, particularly when inhaled, as its radiation can cause lung disease and cancer. Most plutonium isotopes have long half-lives, and plutonium-239 is a key component in nuclear power and weapons, while plutonium-238 powers spacecraft like NASA's probes to distant planets.

Plutonium is primarily used as fuel in nuclear reactors, in nuclear weapons, and as a heat source in radioisotope thermoelectric generators (RTGs) for spacecraft. Plutonium-239 is the main isotope used for these purposes, either by itself or blended with uranium as MOX fuel. Plutonium-238 provides heat for RTGs, powering devices from satellites to interplanetary probes.

Summary

Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous.

Plutonium was first synthesized and isolated in late 1940 and early 1941, by deuteron bombardment of uranium-238 in the 1.5-metre (60 in) cyclotron at the University of California, Berkeley. First, neptunium-238 (half-life 2.1 days) was synthesized, which then beta-decayed to form the new element with atomic number 94 and atomic weight 238 (half-life 88 years). Since uranium had been named after the planet Uranus and neptunium after the planet Neptune, element 94 was named after Pluto, which at the time was also considered a planet. Wartime secrecy prevented the University of California team from publishing its discovery until 1948.

Plutonium is the element with the highest atomic number known to occur in nature. Trace quantities arise in natural uranium deposits when uranium-238 captures neutrons emitted by decay of other uranium-238 atoms. The heavy isotope plutonium-244 has a half-life long enough that extreme trace quantities should have survived primordially (from the Earth's formation) to the present, but so far experiments have not yet been sensitive enough to detect it.

Both plutonium-239 and plutonium-241 are fissile, meaning they can sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Plutonium-240 has a high rate of spontaneous fission, raising the neutron flux of any sample containing it. The presence of plutonium-240 limits a plutonium sample's usability for weapons or its quality as reactor fuel, and the percentage of plutonium-240 determines its grade (weapons-grade, fuel-grade, or reactor-grade). Plutonium-238 has a half-life of 87.7 years and emits alpha particles. It is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft. Plutonium isotopes are expensive and inconvenient to separate, so particular isotopes are usually manufactured in specialized reactors.

Producing plutonium in useful quantities for the first time was a major part of the Manhattan Project during World War II that developed the first atomic bombs. The Fat Man bombs used in the Trinity nuclear test in July 1945, and in the bombing of Nagasaki in August 1945, had plutonium cores. Human radiation experiments studying plutonium were conducted without informed consent, and several criticality accidents, some lethal, occurred after the war. Disposal of plutonium waste from nuclear power plants and dismantled nuclear weapons built during the Cold War is a nuclear-proliferation and environmental concern. Other sources of plutonium in the environment are fallout from many above-ground nuclear tests, which are now banned.

Details

Plutonium (Pu) is a radioactive chemical element of the actinoid series of the periodic table, atomic number 94. It is the most important transuranium element because of its use as fuel in certain types of nuclear reactors and as an ingredient in nuclear weapons. Plutonium is a silvery metal that takes on a yellow tarnish in air.

The element was first detected (1941) as the isotope plutonium-238 by American chemists Glenn T. Seaborg, Joseph W. Kennedy, and Arthur C. Wahl, who produced it by deuteron bombardment of uranium-238 in the 152-cm (60-inch) cyclotron at Berkeley, California. The element was named after the then planet Pluto. Traces of plutonium have subsequently been found in uranium ores, where it is not primeval but naturally produced by neutron irradiation.

All plutonium isotopes are radioactive. The most important is plutonium-239 because it is fissionable, has a relatively long half-life (24,110 years), and can be readily produced in large quantities in breeder reactors by neutron irradiation of plentiful but nonfissile uranium-238. Critical mass (the amount that will spontaneously explode when brought together) must be considered when handling quantities in excess of 300 grams (2/3 lb). The critical mass of plutonium-239 is only about one-third that of uranium-235.

Plutonium and all elements of higher atomic number are radiological poisons because of their high rate of alpha emission and their specific absorption in bone marrow. The maximum amount of plutonium-239 that can be indefinitely maintained in an adult without significant injury is 0.008 microcurie (equal to 0.13 microgram [1 microgram = {10}^{-6} gram]). Longer-lived isotopes plutonium-242 and plutonium-244 are valuable in chemical and metallurgical research. Plutonium-238 is an alpha-emitting isotope that emits a negligible amount of gamma rays; it can be manufactured to harness its heat of radioactive decay to operate thermoelectric and thermionic devices that are small, lightweight, and long-lived (the half-life of plutonium-238 is 87.7 years). The power produced from plutonium-238 alpha decay (approximately 0.5 watt per gram) has been used to provide spacecraft electrical power (radioisotope thermoelectric generators [RTGs]) and to provide heat for batteries in spacecraft, such as in the Curiosity rover.

Plutonium exhibits six forms differing in crystal structure and density (allotropes); the alpha form exists at room temperature. It has the highest electrical resistivity of any metallic element (145 microhm-centimetres). Chemically reactive, it dissolves in acids and can exist in four oxidation states as ions of characteristic colour in aqueous solution: Pu3+, blue-lavender; Pu4+, yellow-brown; PuO2+, pink; yellow or pink-orange; and Pu7+, green. Very many compounds of plutonium have been prepared, often starting from the dioxide (PuO2), the first compound of any synthetic element to be separated in pure form and in weighable amounts (1942).

Element Properties

atomic number  :  94
stablest isotope  :  244
melting point  :  639.5 °C (1,183.1 °F)
boiling point  :  3,235 °C (5,855 °F)
specific gravity (alpha)  :  19.84 (25 °C)
oxidation states  :  +3, +4, +5, +6.

Additional Information:

Appearance

A radioactive, silvery metal.

Uses

Plutonium was used in several of the first atomic bombs, and is still used in nuclear weapons. The complete detonation of a kilogram of plutonium produces an explosion equivalent to over 10,000 tonnes of chemical explosive.

Plutonium is also a key material in the development of nuclear power. It has been used as a source of energy on space missions, such as the Mars Curiosity Rover and the New Horizons spacecraft on its way to Pluto.

Biological role

Plutonium has no known biological role. It is extremely toxic due to its radioactivity.

Natural abundance

The greatest source of plutonium is the irradiation of uranium in nuclear reactors. This produces the isotope plutonium-239, which has a half-life of 24,400 years.

Plutonium metal is made by reducing plutonium tetrafluoride with calcium.

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