The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Bibliographic Entry||Result |
|Cutnell, John D. and Johnson, Kenneth W. Physics, 3rd edition. New York: Wiley, 1995, 1013.||"Plutonium is the final product and has half-life of 24,100 yr"||24,100 year|
|"Plutonium." Microsoft Encarta 97 Encyclopedia. CD-ROM. Microsoft. 1993-1996.||"The most important isotope, Pu-239, has a half life of 24,360 years"||24,360 year|
|Knapp, Brian. Nuclear Physics. United States: Atlantic Europe, 1996, 26.||"Plutonium, a silvery metal with a half-life of 24,000 years"||24,000 year|
|Cleveland, J. M. The Chemistry of Plutonium. New York: Gordon & Beach, 1970: 57.||"Pu-239, the more common isotope of Plutonium has a half life of 24,000 years"||24,000 year|
|IEER Plutonium Factsheet. Institute for Energy and Environmental Research.||"For instance, plutonium-239 has a half-life of 24, 110 years while plutonium-241 has a half-life of 14.4 years."||24,110 year |
Plutonium belongs to the class of elements called transuranicelements whose atomic number is higher than 92, the atomic numberof uranium. Plutonium is the most economically important of thetransuranic elements. Plutonium-239 readily undergoes fission,and it is used for nuclear weapons and for energy. The atomicnumber of plutonium is 94. Isotopes of plutonium were first preparedand studied by the American chemist Glenn T. Seaborg and his associatesat the University of California at Berkeley in 1941. Plutoniumhas 15 isotopes with mass numbers ranging from 232 to 246. Allisotopes of plutonium are radioactive, but they have widely varyinghalf-lives. The half-life is the time it takes for half the atomsof an element to decay. The various isotopes also have differentprincipal decay modes.
The most important isotope of plutonium is Pu-239. It's virtuallynonexistent in nature. It is produced by bombarding uranium-238with slow neutrons. This forms neptunium-239, which in turn emitsa beta particle and forms plutonium-239. Plutonium-239's principalmode of decay is alpha decay. Various sources give slightly differentfigures for the half-life. The values found include 24,360, 24,400,24,110, and 24,000 years. None of theses measurements agree.It is because there are many factors that can affect the accuracyof this measurement. Plutonium-239 is produced artificially, andevery time it is produced, it is mixed with varying amounts ofother isotopes, notably plutonium-240, plutonium-241 and plutonium-242.Since all the isotopes have nearly the same chemical characteristics,it is very difficult to separate isotopes from each other by chemicaltechniques. This means, it is virtually impossible to study theproperties of pure Plutonium-239. Therefore, the results mightbe the average half-life of it being mixed with a small amountof the other isotopes. And there will be a slight difference inthe density and purity of it every time it is being produced,depending upon the amount of reactants used in the process ofits production. In addition, a little spontaneous fission occursin most plutonium isotopes. So while some of the Plutonium-239atoms are undergoing decay, a small number of them are splittinginto less-massive nuclei. The rate of fission is not a constant.
Plutonium-239 is a fissile material. It can be split by bothslow and fast neutrons. Each fission of this isotope resultingfrom a slow neutron absorption results in the production of alittle more than two neutrons. If one of these neutrons, on average,splits another plutonium nucleus, a sustained chain reaction isachieved. So the source of neutrons can have big influence onthe outcome of an experiment.
Janice Ching -- 1999
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