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Isotopes
212202219
Isotopes and Centrifugation
Originally by Concord Consortium Staff and modified by Ed O'Sullivan, Brookfield Academy
Uranium has an atomic number of 92, atomic mass of 238.02891, and three naturally occurring isotopes , 234U, 235U, and 238U.
Uranium is used as a fuel in nuclear reactors in a process called nuclear fission. However, of the three uranium isotopes, only uranium-235 is fissionable and can serve as a fuel. This is problematic because naturally occurring uranium contains only a very small percentage of 235U (natural abundances: 0.0055% 234U, 0.72% 235U, and 99.27% 238U). As you can see, uranium-235 composes less than 1% of naturally occurring uranium. To be used as a fuel it needs to be at least around 3%. In other words, the uranium needs to be enriched in uranium-235. One technique to accomplish such a task is known as centrifugation.
To "increase gravity" a machine called a centrifuge (shown below) spins the mixture around so fast that a gravity-like force is created within the test tube that is up to 300,000 times stronger than that of Earth's gravity. This amplified force aids in the separation of substances by density.
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<font face="Verdana" size="3">How many protons are there in <sup>234</sup>U,
<sup>235</sup>U, and <sup>238</sup>U respectively?</font>
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<font face="verdana" size="3">How many neutrons are there in <sup>234</sup>U,
<sup>235</sup>U, and <sup>238</sup>U respectively?</font>
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<font face="verdana" size="3">Based upon the atomic mass of uranium, which
isotope of uranium do you think is most abundant?</font>
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<font face="Verdana,sans-serif" size="4"><strong>Centrifugation</strong>
is a technique used to separate substances by density. Since density is
defined as mass over volume, when comparing two substances of the same
volume, the one with the higher mass will have the higher density. Since
atoms of different isotopes of the same element have the same volume, the
heavier isotope will have the higher density. For our purposes, this means
the <sup>238</sup>U is more dense than <sup>235</sup>U. </font>
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isotopes2.cml