PHY213_Chapter30_Sec1to2

PHY213_Chapter30_Sec1to2 - Chapter 30 Nuclear Energy...

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Chapter 30 Nuclear Energy
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General Physics Nuclear Energy Sections 1–2
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General Physics Processes of Nuclear Energy Fission A nucleus of large mass number splits into two smaller nuclei The total mass of the fission products is less than the original mass of the heavy nucleus Fusion Two light nuclei fuse to form a heavier nucleus The mass of the fusion product is less than the total mass of the original two light nuclei Large amounts of energy are released in either case
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General Physics Nuclear Fission Equation Fission of 235 U by a slow (low energy) neutron 236 U* is an intermediate, short-lived state Lasts about 10 -12 s X and Y are called fission fragments Many combinations of X and Y satisfy the requirements of conservation of energy and charge 1 235 236 0 92 92 * n U U X Y neutrons + ++
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General Physics More About Fission of 235 U About 90 different daughter nuclei can be formed Several neutrons are also produced in each fission event Example: The fission fragments and the neutrons have a great deal of KE following the event 1 235 141 92 1 0 92 56 36 0 3 n U Ba Kr n +→ + +
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General Physics Sequence of Events in Fission The 235 U nucleus captures a thermal (slow-moving) neutron This capture results in the formation of 236 U*, and the excess energy of this nucleus causes it to undergo violent oscillations The 236 U* nucleus becomes highly elongated, and the force of repulsion between the protons tends to increase the distortion The nucleus splits into two fragments and several neutrons
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General Physics Energy in a Fission Process Binding energy for heavy nuclei is about 7.2 MeV per nucleon Binding energy for intermediate nuclei is about 8.2 MeV per nucleon Therefore, the fission fragments have less mass than the nucleons in the original nuclei This decrease in mass per nucleon appears as released energy in the fission event
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General Physics An estimate of the energy released Assume a total of 240 nucleons Releases about 1 MeV per nucleon 8.2 MeV – 7.2 MeV Total energy released is about 240 MeV This is very large compared to the amount of energy released in chemical processes Energy in a Fission Process, cont
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General Physics Chain Reaction Neutrons are emitted when 235 U undergoes fission These neutrons are then available to trigger fission in other nuclei This process is called a chain reaction If uncontrolled, a violent explosion can occur The principle behind the nuclear bomb, where 1 kg of U can release energy equal to about 20,000 tons of TNT
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General Physics Chain Reaction – Diagram Active Figure: A Nuclear Chain Reaction
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This note was uploaded on 08/25/2009 for the course PHY 213 taught by Professor Cao during the Summer '08 term at Kentucky.

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PHY213_Chapter30_Sec1to2 - Chapter 30 Nuclear Energy...

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