45_fissionfusion - Lesson 45 Fission Fusion Start talking...

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Start talking to someone about nuclear energy, and they’ll probably think of two things: nuclear bombs, and the towers of a nuclear power plant like on the Simpsons. Most people view nuclear energy as something to be afraid of, but like most things, once you understand it a lot of the fear disappears. There are two main types of nuclear reactions that can release energy: Fission : The process of causing a large nucleus (A > 120) to split into multiple smaller nuclei, releasing energy in the process. It can start when the large nuclei absorbs a neutron, causing it to become unstable to the point that it falls apart. This is the reaction that we use in nuclear power plants and early nuclear weapons. Fission is relatively easy to do, but also leaves us with lots of nuclear waste that must be stored for thousands of years before it is safe. Fusion : The process of causing small nuclei to stick together into a larger nucleus, in the process releasing energy. This is the process that drives our sun, and all other suns. We can do it under the right conditions in a lab, but we end up putting in more energy than we get out. The left over products of fusion are relatively safe, which is why a lot of research is going into developing fusion reactors. Fission The most typical fuel used in a fission reactor is uranium-235. In 1939 four German scientists discovered that uranium-235 would become very unstable if it gained an extra neutron, forming uranium-236. Uranium-236 is so unstable that a fraction of a second later it will split to form two smaller atoms, and in the process release energy. Here are two common fission reactions that uranium-236 can go through. .. U 92 235 n 0 1 U 92 236 Ba 56 141 Kr 36 92 3 n 0 1 and U 92 235 n 0 1 U 92 236 Xe 54 140 Sr 38 94 2 n 0 1 Some things to notice… 1. Both reactions start the same when we add a single neutron to uranium-235, which forms uranium-236 for a split second. 2. Barium-141, krypton-92, xenon-140, and strontium-94 are smaller nuclei that uranium-236 could split into. 3. At any point in the reaction the conservation of nucleons stays the same. 4.
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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45_fissionfusion - Lesson 45 Fission Fusion Start talking...

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