Nuclear Energy
Nuclear Reactions
Nuclear Fission / Nuclear Fusion
Harnessing the Power of the Nucleus
Unstable Atomic Nuclei
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Shortly after the discovery of
radioactivity by Becquerel, scientists
discovered that the nucleus of an atom
contained huge amounts of potential
energy
WHY?
Unstable Atomic Nuclei
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A nucleus becomes unstable when the
strong nuclear force is not strong
enough to overcome the repulsion of
protons
All atoms with atomic numbers greater
than 82 are radioactive

Radioactive: unstable nucleus emits
energy when it breaks into smaller parts
Types of Nuclear Radiation
Radioactive Decay Rates
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Half Life: The time it takes for half of a
radioactive sample to decay
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In one half life, half of the radioactive
atoms decay & half are left unchanged
In the next half life (2 half lives), half of
the remaining atoms decay

Only ¼ of the original sample is now left
unchanged
Radioactive Decay Rates
Half Life
Nuclear Fission
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Proposed / explained by Lise Meitner &
Otto Frisch in 1939
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Based on work by Meitner & Hahn
Definition: Splitting of a larger atomic
nucleus into smaller nuclei
Tremendous amounts of energy are
released from very small amounts of
mass
Two smaller nuclei that are not radioactive are created
Fast moving neutron
runs into a radioactive
nucleus
Why use a neutron?
Also released: 2 or 3 stray
Neutrons have no charge – their
motion will not change as they move
neutrons and LOTS of
closer to the nucleus
energy!!
Mass-Energy Equation

Proposed by Einstein in 1905 (long
before fission or fusion were
discovered)
 E = mc2
 E: Energy
 m: mass
8
 c: speed of light (3.010 m/s)
Mass-Energy Equation
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What does it mean?
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Mass and energy are two forms of the
same thing
Under the right conditions, mass can be
converted into energy and energy can be
converted into mass
When mass is converted into energy,
tremendous amounts of energy are
released from very small amounts of mass
Chain Reactions
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The neutrons released during fission can
be used to split other unstable atoms
Left unchecked, a chain reaction can
release huge amounts of energy
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Atomic Bombs
Nuclear Reactors use a controlled chain
reaction where the number of neutrons
that split other unstable atoms is limited
Chain Reactions
(Nuclear Reactors)
Steam turns generator
Electricity is created
Fission
reaction
occurs
Energy
released
turns
water into
steam
Nuclear Fusion


Two small nuclei are combined to form
a nucleus with a greater atomic number
A small amount of mass is converted to
energy during fusion

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Mass-Energy equation says small amounts
of mass produces large amounts of energy
Fusion requires extremely high
temperatures (WHY?)
The only way to get them to stay close
together is to raise the temperature
really high to make them move really
fast
Both small nuclei are
positively charged –
they repel
When they combine,
a small amount of
mass turns to a
HUGE amount of
energy