8.4.7. - Describe how neutron capture by a nucleus of uranium-238 (238U) results in the production of a nucleus of plutonium-239 (239Pu).

1. Uranium-238
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A sample of Uranium-238

Uranium-238, with 146 neutrons and 92 protons, is the most common isotope of uranium to be found in nature, comprising 99.284% of the extant naturally occurring uranium. However, as opposed to uranium-235, which is much rarer than uranium-238, uranium-238 is not fissile and therefore cannot sustain a chain reaction, from which huge amounts of energy is created; although uranium-238 is fissionable (able to undergo nuclear fission), the neutrons created by the initial fission are not fast enough to produce new fissions. Therefore, uranium-238 is not a nuclear fuel.


2. Neutron capture
However, that uranium-238 is not fissile does not render uranium-238 useless for the production of nuclear power. This is because uranium-238 can undergo what is know as neutron capture. Neutron capture describes a situation in which a neutron comes close to a nucleus (in this case uranium) and the nucleus captures it and becomes a different nucleus.

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In this case, uranium-238 captures a neutron and it becomes uranium-239, with 147 neutrons. After uranium-239 emits a beta particle (electron) it becomes neptunium-239, with 93 protons. Then, neptunium-239 emits a beta particle and becomes plutonium-239, with 94 protons. As discovered by Glenn Seaborg, Joe Kennedy, Art Wahl, and Emilio Segrè, the resultant plutonium-239 can be used as nuclear fuel, being fissile.
Neutron capture can be performed in what is called breeder reactor.
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The fissioning of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be absorbed by uranium-238 to produce plutonium-239

8.4.8 - Describe the importance of plutonium-239 (239Pu) as a nuclear fuel.

Plutonium-239
Plutonium-239 (Pu-239) is one of the three fissile isotopes used for the nuclear reactors as a source of energy. Other fissile isotopes used are uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years. The nuclear properties of plutonium-239, as well as the ability to produce large amounts of nearly pure plutonium-239, led to its use in nuclear weapons and nuclear power. The fissioning of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be absorbed by uranium-238 to produce plutonium-239 and other isotopes. Plutonium fissions provide about one-third of the total energy produced in a typical commercial nuclear power plant. The use of plutonium-239 in power plants occurs without it ever being removed from the nuclear reactor fuel, i.e., it is fissioned in the same fuel rods in which it is produced.
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Plutonium Sampte


Works Cited
CRC Handbook, 57th Ed. p. B-345
Giancoli, Douglas C. Physics Principles With Applications. 5th ed. Upper Saddle River: Prentice Hall, 2002.
McClain, D. E., A. C. Miller, and J. F. Kalinich. Status of Health Concerns about Military Use of Depleted Uranium and Surrogate Metals in Armor-Penetrating Munitions. Rep. 2005. Armed Forces Radiobiology Research Institute. 2 Apr. 2009 <http://www.afrri.usuhs.mil/www/outreach/pdf/mcclain_NATO_2005.pdf>.
"Nuclear Power Education - The Science of Nuclear Power." Nuclear Power Education. 2009. The University of Melbourne. 2 Apr. 2009 <http://nuclearinfo.net/Nuclearpower/TheScienceOfNuclearPower>."What is it? - HBO Films: PU-239." HBO Online. 02 Apr. 2009 <http://www.hbo.com/films/pu239/specialfeature/index.html>.