plutonium

plutonium C화학적 특성, 용도, 생산

물리적 성질

All isotopes of plutonium are radioactive. The two isotopes that have found the most usesare Pu-238 and Pu-239. Pu-238 is produced by bombarding U-238 with deuterons in acyclotron, creating neptunium-238 and two free neutrons. Np-238 has a half-life of abouttwo days, and through beta decay it transmutates into plutonium-238. There are six allotropicmetallic crystal forms of plutonium. They all have differing chemical and physical properties.The alpha (α) allotrope is the only one that exists at normal room temperatures and pressures.The alpha allotrope of metallic plutonium is a silvery color that becomes yellowish as it oxidizesin air. All the other allotropic forms exist at high temperatures.
The most stable isotope of plutonium is Pu-244, with a half-life of 8.00×10⁺⁷years (about82,000,000 years). Being radioactive, Pu-244 can decay in two different ways. One wayinvolves alpha decay, resulting in the formation of the isotope uranium-240, and the other isthrough spontaneous fission.
The melting point of plutonium is 640°C, its boiling point is 3,232°C, and its density isover 19 times that of the same volume of water (19.84g/cm³).

Isotopes

There are a total of 24 isotopes of plutonium. All of them are unstable andradioactive. Their half-lives range from 28 nanoseconds to 8.00×10⁺⁷years.

Origin of Name

Named for the planet Pluto.

출처

Plutonium exists in trace amounts in nature. Most of it isotopes are radioactive and manmadeor produced by the natural decay of uranium. Plutonium-239 is produced in nuclearreactors by bombarding uranium-238 with deuterons (nuclei of deuterium, or heavy hydrogen).The transmutation process is as follows: 238U + deuterons→ 2 nuclei + ²³⁹Np + β→decays to→ ²³⁸Pu + β-.
There is more than an adequate supply of plutonium-239 in the world because it is a“waste” product of the generation of electricity in nuclear power plants. One of the objectionsto developing more nuclear reactors is the dilemma of either eliminating or storing allthe excess plutonium. In addition, there is always the risk of terrorists’ obtaining a supply ofPu-239 to make nuclear weapons.

용도

The most common use of plutonium is as a fuel in nuclear reactors to produce electricity oras a source for the critical mass required to sustain a fission chain reaction to produce nuclearweapons. Plutonium also is used to convert nonfissionable uranium-238 into the isotopecapable of sustaining a controlled nuclear chain reaction in nuclear power plants. It takesonly 10 pounds of plutonium-239 to reach a critical mass and cause a nuclear explosion, ascompared with about 33 pounds of fissionable, but scarce, uranium-235.
Plutonium-238 and plutonium-239 are two isotopes that can be used outside of thenuclear weapons industry. Plutonum-238 is currently used in small thermoelectric generatorsto provide electricity for space probes that are sent far beyond the region where the sun couldbe used to generate electric power. Two early instruments sent beyond our solar system arethe Galileo and Cassini probes. Plutonium-239’s critical mass undergoes a fissionable chainreaction, making it ideal for use as fuel for some types of nuclear reactors as well as to producenuclear weapons. In the future it may be possible to use all the waste plutonium produced inthe world to power small thermal electrical power plants that could be installed in each houseto provide inexpensive and continuous household electrical power. This probably will nothappen until the public overcomes its fear of nuclear energy.

정의

A radioactive silvery element of the actinoid series of metals. It is a transuranic element found on Earth only in minute quantities in uranium ores but readily obtained, as ²³⁹Pu, by neutron bombardment of natural uranium. The readily fissionable ²³⁹Pu is a major nuclear fuel and nuclear explosive. Plutonium is highly toxic because of its radioactivity; in the body it accumulates in bone. Symbol: Pu; m.p. 641°C; b.p. 3232°C; r.d. 19.84 (25°C); p.n. 94; most stable isotope ²⁴⁴Pu (half-life 8.2 × 107 years).

위험도

Plutonium is by far one of the most toxic radioactive poisons known. The metal, its alloys,and its compounds must be handled in a shielded and enclosed “glove box” that contains an inertargon atmosphere. It is a carcinogen that can cause radiation poisoning leading to death.

공업 용도

Plutonium is made from uranium-238 byabsorption of neutrons from recycled fuel. Themetal, 99.8% pure, is obtained by reduction ofplutonium fluoride, PuF₄, or plutonium chloride,PuCl₃. Plutonium-238 has a low radiationlevel and is used as a heat source for smallwater-circulating heat exchangers for navalundersea diving suits.
Plutonium-241 emits beta and gamma rays.Because all the allotropic forms are radioactive,it is a pure nuclear fuel in contrast touranium, which is only 0.7% directly usefulfor fission. It is thus necessary to dilute plutoniumfor control. For fuel elements it may bedispersed in stainless steel and pressed intopellets at about 871°C, or pellets may be madeof plutonium carbide. Plutonium–iron alloy,with 9.5% iron, melts at 410°C. It is encasedin a tantalum tube for use as a reactor fuel.Plutonium–aluminum alloy is also used.

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