Plutonium

Plutonium Chemische Eigenschaften,Einsatz,Produktion Methoden

• Beschreibung

  Plutonium was first isolated and produced in 1941 at the University of California-Berkeley, by nuclear chemist Glenn T. Seaborg and his colleagues, Joseph W. Kennedy, Edwin M. McMillan, and Arthur C. Wahl. Minute amounts of plutonium exist naturally, but large amounts are produced in nuclear reactors when uranium absorbs an atomic particle such as a neutron.
  Natural occurrences of plutonium are very rare, but it can occur in a reaction called spontaneous fission. This type of reaction occurs when ores of uranium with a high localized concentration decay in the right conditions and produce small amounts of plutonium. Synthetic plutonium is produced in a controlled nuclear reactor when uranium-238 absorbs a neutron and becomes uranium-239, ultimately decaying to plutonium-239. Plutonium has at least 15 different isotopes. Different isotopes of uranium and different combinations of neutron absorption and radioactive decay create the different isotopes of plutonium. Plutonium was discovered during wartime; therefore, the majority of plutonium production was for nuclear weapons. Other plutonium applications range from being energy sources on deep space probes to small amounts providing power to heart pacemakers.

• Chemische Eigenschaften

  silvery white metal; highly reactive; αform: monoclinic, a=0.6183 nm, b=0.4822 nm, c=1.0963 nm; ionic radius of Pu++++ is 0.0887nm; stable form from room temp to 115°C; enthalpy of vaporization 333.5kJ/mol; enthalpy of fusion 2.82kJ/mol; discovered in 1940–1941; prepared in ton quantities in nuclear reactors; 238Pu produced in kg amounts from 237Np; important fuel for producing power for terrestrial and extraterrestrial applications [MER06] [KIR78] [CRC10]

• History

  The name of Pu derives from the planet Pluto, (the Roman god of the underworld). Pluto was selected because it is the next planet in the solar system beyond the planet Neptune and the element plutonium is the next element in the period table beyond neptunium. Plutonium was first synthesized in 1940 by American chemists Glenn T. Seaborg, Edwin M. McMillan, Joseph W. Kennedy and Arthur C. Wahl at Berkeley, California, in the nuclear reaction ²³⁸U(²H, 2n) ²³⁸Np → β − → ²³⁸Pu. The longest half-life associated with this unstable element is 80 million year ²⁴⁴Pu.

• Verwenden

  The principal plutonium isotopes, ²³⁹Pu and ²⁴⁰Pu, were produced as ingredients for nuclear weapons. It is estimated that the United States produced 400 kCi of plutonium for nuclear weapons testing, and approximately 325 kCi was dispersed globally into the environment from conducted aboveground tests. Overall, an estimated 500 aboveground nuclear tests were conducted between 1945 and 1963 by the Soviet Union, Britain, France, and the United States. From these tests, it is estimated 100 000 kCi of plutonium were dispersed into the environment.
  Applications for 238Pu include using it as a heat source for thermoelectric power devices. Radioisotope thermoelectric generators (RTGs) have been used to provide a source of power in remote locations, such as deep space probes. This plutonium isotope generates a large amount of heat through its decay process. The generated heat is converted into electric power via a thermocouple in the RTG. Small-scale application of ²³⁸Pu is also used to provide power to heart pacemakers. The concept behind the use of this material is a result of the half-life of the isotope, since its half-life is extremely long, changing out the power source is not necessary.

• Definition

  ChEBI: Plutonium atom is an actinoid atom and a f-block element atom.

• Environmental Fate

  Plutonium was dispersed in the environment by fallout from aboveground weapons testing that occurred from the 1940s through the 1960s. Approximately one-fifth of the plutonium fallout from a nuclear weapons test remained on the test site. The remaining plutonium fallout was released into the atmosphere, absorbed to particulate matter, and transported back to the surface by either dry or wet deposition. Additional releases can be traced to accidental reactor effluent releases, improper disposal of radioactive waste, and military accidents. Each release directly introduced plutonium into the ecosystem, where it has stayed.
  Plutonium and its isotopes have relatively long half-lives. The most common plutonium isotopes are ²³⁸Pu, ²³⁹Pu, and ²⁴⁰Pu. The decay process for each of these varies, and all are extremely long in duration. ²³⁸Pu (the principal isotope for satellites) has a half-life of 87.7 years, ²³⁹Pu (a principal isotope for nuclear weapons) has a half-life of 24 100 years, and ²⁴⁰Pu has a half-life of 6560 years. Plutonium undergoes a change in form through radioactive decay. As each of these isotopes decay, they release energy and form a new product. The energy being released is referred to as radiation. Plutonium reactions in the environment are either oxidative or reductive reactions. Plutonium can be found in five different oxidations states: plutonium(III), plutonium(IV), plutonium( V), plutonium(VI), and plutonium(VII).
  Most atmospheric and underwater nuclear weapons testing were stopped by the Partial Test Ban Treaty of 1963. The treaty did not cease the testing of nuclear weapons, it only banned testing aboveground, and the testing continued underground until the 1980s. Although the move to test underground was to reduce the release of plutonium into the environment, releases still occurred via test venting. Plutonium can migrate vertically at various rates depending on meteorological conditions, the form of plutonium as it enters the environment, and human activity. However, almost all plutonium introduced into the environment can be found in the surface soil. Soil particles are the primary mode of distribution. Plutonium compounds are ionic and will not volatilize from the soil. Surface soils contaminated with plutonium have been known to resuspend in the atmosphere via fugitive dust emissions, causing it to be rereleased into the environment. Parameters such as particle size, presence of organic substances, and soil pH can influence the distribution of the plutonium isotopes in the soil and sediment. It has been documented in arctic surface sediment studies that the partition coefficients (Kd) for ^239，240Pu range from 8 × 10⁺⁴ to 1.5 × 10⁺⁵. Plutonium fallout from the atmosphere can be deposited as insoluble dioxide. This is an important factor since microorganisms can change the oxidation state of plutonium, potentially causing it to increase or decrease in solubility. But microorganism changes occur only in a small fraction of the plutonium released into the environment and this is based on the released plutonium form. If the plutonium does enter the soluble phase, it can become available for plant uptake. Studies have shown that the plutonium(IV) oxidation state is able to hydrolyze in the environment, and plants can readily uptake the contaminant.
  Atmospheric plutonium fallout can reach surface water and settle in the sediment under the water. The long halflives of plutonium isotopes allow for contaminated sediment to act as a repository, and eventually the contaminants can resuspend in the water column, reintroducing them into the environment. How plutonium in surface water acts is dependent on the oxidation state of the released plutonium and the nature of the suspended particulates in the environment. It has been reported that plutonium in water with suspended solids have Kd values ranging fro

• Toxicity evaluation

  The toxicity of plutonium is based on the radiation emitted during the exposure and radiological decay of the plutonium isotope. Radiation emitted by plutonium can have many different mechanistic impacts on cells, including ionization and destruction of cell constituents that can result in a variety of effects ranging from cell death with/without regeneration to cells growing out of control if the DNA damage resulting is not arrested by normal healthy body repair mechanisms. Additional factors of toxicity include the radiosensitivity of the tissue exposed and the retention time. Tissues that undergo rapid cell regeneration are more sensitive than slower or nonregenerating cells.

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