Lesson 29: Nuclear Fission and Fusion!
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Fission!
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Fusion!
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Part 1: Fission of Uranium !
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Uranium-235 is a common fuel used for fission to produce nuclear energy!
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The process:!
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Equations:!
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Chain reaction:!
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The fission in a nuclear reactor is self sustaining. !
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If the neutrons are shielded and reflected back into the
uranium for long enough, about 1.0 ms, the reaction
results in an atomic explosion. However, a controlling
device can be used to control and reduce the rate of
the reaction. A stable controlled reaction produces
heat that can be used to heat water into steam and
then drive a steam turbine to create electricity. Candu
reactors use heavy water to slow down the chain
reaction rate and to control the overall reaction. !
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Example: Calculate the energy released in one fission of uranium-235 into krypton-92 and barium-141!
uranium-235
235.0439299 u
kripton-92
91.92615621 u
barium-141
140.914411009 u
neutron
1.00866491600 u
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Part 2: Fusion of Hydrogen!
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In nuclear fusion we take light elements and force them together to
form larger sized atoms.!
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Nuclear fusion reactions require extremely high pressures and
temperatures to get them started. Such pressures and temperatures
are found within the core of a star like our Sun. In a star the nuclei are
forced together due to the enormous gravitational forces involved. In
turn, the forces created by the fusion reactions try to explode the star.
Thus there is a balance between the forces of gravity and the forces
produced by the fusion reactions.!
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Hydrogen fusion in the sun:!
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Example: Calculate the energy released as hydrogen fuses with deuterium (hydrogen-2) to produce
helium-3.!
hydrogen
1.00782503207 u
deuterium
2.01410177785 u
helium-3
3.01602931914 u
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Element Formation in Stars!
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75% of the matter in the universe is in the form of hydrogen. In fact, it
is from hydrogen that all elements are eventually synthesized. This
process occurs through a series of fusion reactions within stars. Our
Sun is an average star that is currently half way
through its life cycle. The main reaction that
powers the Sun’s energy is a series of reactions
leading to the formation of helium from
hydrogen.!
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Some of the elements larger than helium can be
produced by fusion in stars larger than our sun. !
Other larger elements can only be produced in
huge energetic events like supernovae. !
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Practice Problems!
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3. Calculate the energy released by the reaction. ! !
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235
92
U + 01n →
94
40
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[answer = 2.93 x 10-11 J]!
[answer = 2.83 x 10-12 J]!
[answer = 172.9 MeV]!
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Zr + 139
52Te + 3 0 n
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Masses: uranium-235 = 235.043930, n = 1.008665, zirconium-94 = 93.906315, !
tellurium-139 = 138.934700! !
1 u = 1.660539 x 10-27 kg!
4.
A uranium-235 nucleus absorbs a neutron and the splits into a bromine-87 nucleus, a
lanthanum-146 nucleus and additional neutrons. How many neutrons are released and what is the
energy released in the reaction? [3 neutrons, 167.8 MeV] (Bromine-87 = 86.920711 u,
lanthanum-146 = 145.925791)!
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5. A neutron is emitted when aluminum-27 absorbs an alpha particle.
reaction.!
Write the process for this
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6. Write the reaction for the fusion of helium-4 with oxygen-16. How much energy does this reaction
release? [4.730 MeV]!
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Helium 4 = 4.002603 u!
7. Given the following masses !
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Hydrogen-2 2.0141 u! !
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neutron = 1.0087 u! !
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oxygen-16 = 15.994915 u
neon-20 = 19.992440 u!
hydrogen-3 3.0161 u! !
helium 4 = 4.0026 u!
Determine the energy produced in the following fusion reaction: [answer = 2.82 x 10-12 J]!
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H + 13 H → 24 He + 01n