atomic energy 3u physics. mass-energy equivalence all matter is a form of stored energy
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Atomic Energy
3U Physics
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Mass-Energy Equivalence
All matter is a form of stored energy.
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Mass-Energy Equivalence
All matter is a form of stored energy.
If matter of mass m is converted to energy, the amount of energy E that can be released is equal to:
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Mass-Energy Equivalence
All matter is a form of stored energy.
If matter of mass m is converted to energy, the amount of energy E that can be released is equal to:
E = mc2
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Mass-Energy Equivalence
All matter is a form of stored energy.
If matter of mass m is converted to energy, the amount of energy E that can be released is equal to:
E = mc2
c = 3.0 x 108 m/s
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Mass-Energy Equivalence: Example
What is the energy equivalent of a 52 kg person?
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Mass-Energy Equivalence: Example
What is the energy equivalent of a 52 kg person?
?
100.3
528
E
c
kgm
sm
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Mass-Energy Equivalence: Example
What is the energy equivalent of a 52 kg person?
?
100.3
528
E
c
kgm
sm
JE
kgE
mcE
sm
18
28
2
107.4
100.352
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The Mass Defect
More practically, we look at the energy equivalent of the mass defect.
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The Mass Defect
More practically, we look at the energy equivalent of the mass defect.
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The Mass Defect
Consider a Carbon 12 nucleus:
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The Mass Defect
Consider a Carbon 12 nucleus:6 protons, 1.007276 amu each+ 6 neutrons, 1.008665 amu each
= 12.095646 amu
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The Mass Defect
Consider a Carbon 12 nucleus:6 protons, 1.007276 amu each+ 6 neutrons, 1.008665 amu each
= 12.095646 amu
Actual mass of Carbon 12 nucleus:= 11.996709 amu
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The Mass Defect
The 0.098937 amu mass defect is the binding energy of the nucleus.
E = mc2
E ≈ (0.098937)(1.66 x 10-27 kg)(3.0 x 108 m/s)2
E ≈ 1.5 x 10-11 J
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The Mass Defect
Energy stored in the nucleus can be released in nuclear reactions such as radioactive decay:
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The Mass Defect
Energy stored in the nucleus can be released in nuclear reactions such as radioactive decay:
The energy is released in the form of kinetic energy (of the resulting particles).
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Nuclear Fission
However, in a nuclear reactor, we don’t sit around waiting for a radioactive decay.
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Nuclear Fission
However, in a nuclear reactor, we don’t sit around waiting for a radioactive decay. We trigger them by bombarding nuclei with neutrons:
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Nuclear Fission
Notice that the reaction produces more neutrons, which can then bombard more nuclei in a chain reaction:
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Nuclear Fusion
Energy can also be obtained by fusing together light elements, e.g. hydrogen into helium:
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Nuclear Fusion
However, fusing nuclei requires overcoming the electrostatic repulsion between the nuclei.
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Nuclear Fusion
However, fusing nuclei requires overcoming the electrostatic repulsion between the nuclei.
This requires enormous temperatures and pressures such as those produced in the core of the Sun.
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Nuclear Power
The ejected neutron has too much energy to start another nuclear reaction on its own…
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CANDU Reactor
• Fuel rods are surrounded by “heavy water”• Deuterium: istotope of hydrogen with one
neutron• Makes water 11% more dense
• Heavy water heats up; free neutrons slow down
• Chain reaction continues• EK of neutron becomes Eth of water • Steam turns turbine, generates power
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CANDU Reactor
• http://www.youtube.com/watch?v=jNOzh4Kwgpw
• Is it environmentally friendly?
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Radioactive Waste
• Unstable atoms are called “radioactive”
• They have the ability to decay into another substance and emit radiation
• The rate of decay is predictable
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Half-Life
• The average length of time it takes a radioactive material to decay to half its original mass
• Ex. If a 10 kg sample of radioactive material has a half-life of 5 years, how much will be left after 5 years? 10 years?
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Types of Decay
Type of Decay
RadiationEmitted Particle
Penetrating Power
alpha alpha particle helium nucleus
skin or paper (slow moving)
beta negative
beta particle electron a few sheets of aluminum foil
gamma gamma rays photon a few centimetres of lead