Embed Size (px)
Citation preview
Atomic Energy
3U Physics
Mass-Energy Equivalence
All matter is a form of stored energy.
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:
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
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
Mass-Energy Equivalence: Example
What is the energy equivalent of a 52 kg person?
Mass-Energy Equivalence: Example
What is the energy equivalent of a 52 kg person?
?
100.3
528
E
c
kgm
sm
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
The Mass Defect
More practically, we look at the energy equivalent of the mass defect.
The Mass Defect
More practically, we look at the energy equivalent of the mass defect.
The Mass Defect
Consider a Carbon 12 nucleus:
The Mass Defect
Consider a Carbon 12 nucleus:6 protons, 1.007276 amu each+ 6 neutrons, 1.008665 amu each
= 12.095646 amu
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
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
The Mass Defect
Energy stored in the nucleus can be released in nuclear reactions such as radioactive decay:
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).
Nuclear Fission
However, in a nuclear reactor, we don’t sit around waiting for a radioactive decay.
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:
Nuclear Fission
Notice that the reaction produces more neutrons, which can then bombard more nuclei in a chain reaction:
Nuclear Fusion
Energy can also be obtained by fusing together light elements, e.g. hydrogen into helium:
Nuclear Fusion
However, fusing nuclei requires overcoming the electrostatic repulsion between the nuclei.
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.
Nuclear Power
The ejected neutron has too much energy to start another nuclear reaction on its own…
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
CANDU Reactor
• http://www.youtube.com/watch?v=jNOzh4Kwgpw
• Is it environmentally friendly?
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
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?
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
