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Today: Fusion & Review
Exam #3 is a week from today!
1/3 millimeter
Electron Microscope Image of MEMS Force Sensor
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Quiz 8
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Quiz 8
Chemical reactions involve interactions of electrons
The nuclei do not change, elements remain the same!
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Quiz 9
Discuss!
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Quiz 9
These have atomic mass number zero
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Quiz 9
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A question probably on the next quiz
(Which has more mass?)
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Protons and neutrons weigh LESS when bound together!
Mo
re d
ecre
ase
in m
ass
+
0
+++ 0
+
+
00 00 Carbon-12 nucleus,
Mass = 12 u (by definition)
+
0
Single free protonMass = 1.007825 u
Single free neutronMass = 1.008665 u
You need to ADD energy to takeapart a C-12 nucleus
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Uranium-235 decreases in mass during fission
One possible fission reaction is:
U-235 + neutron Ba-141 + Kr-92 + 3 neutrons
Ending mass = 99.9% of starting mass0.1% Missing mass = kinetic energy of products
(and some gamma rays)
Fission of 1000 kilograms of Uranium-235 releases 1 kilogram of mass energyEquivalent to a few days of U.S. electrical needs
(true: free neutrons do increase in mass)
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Clicker question—Mass energy available
Which reaction can potentially release more energy per nucleon
A) More energy can be released per fission event
B) More energy can be released per fusion event
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Immediately, Nuclear Fusion was recognized as an even greater source of energy
High mass atoms can yieldenergy via nuclear fission
Low mass atoms can yieldenergy via nuclear fusion
Energy availablefrom U-235
Energy availablefrom
hydrogen fusion
And of course, hydrogen is a very abundant element!
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Fusion power first harnessed for weapons
Hyrdrogen fusion initiated by “conventional” fission bombs
Fusion bombs or “H-bombs” 100’s of times more powerful than fission bombs
User:Boostin on wikipedia
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Fission energy took 18 months to harnessWe are still waiting for fusion power!!!
Conceptually, fusion is as simple as fissionE.g. the sun shown above
In practice, fusion is way way way way way way way way harder to control in a machine(fusion weapons work well, but not good for a reactor)
ITERMagnetic confinementfusion experiment
The sun is a successfulfusion reactor
http://www.youtube.com/watch?v=SQ9j2cajRo4&feature=related
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Remember to study quizzes for exam!
One topic that we will cover is diffraction and interference of light. Let’s review a little by looking at applications.
We stopped lecture here, because I became confused about exam #3 topics! Exam #3 DEFINITELY contains interference!