9/18/2012
Fusion, Fission, and ½ Life
Objectives
• To compare and contrast nuclear fusion
and nuclear fission
• To calculate the amount of energy
generated by small changes in mass
during nuclear equations
• To compare and contrast chemical and
nuclear reactions
Nuclear Terminology
• Parent isotopes are
the beginning of the
decay process
• Daughter products
are the new atoms
that are made by
decay
• Half Life is the
amount of time in
takes to convert 50%
of parent isotopes
into daughter
products.
Chemical
Reactions
• Involve changes in
electrons
– Acids & Bases,
combustion, displacement
• The same atoms appear
on both sides of the
reaction.
• Follows Dalton’s Law of
Conservation of Mass
• Small amount of energy
generated
– Burning fossil fuels
• Rate can be influenced
by temperature, pressure,
presence of a catalyst
Decay & ½ Life
• The amount of time a
radioactive isotope takes to
decay can vary from a few
seconds to millions of years
• To measure this, scientists
calculate the half life
• 1 Half life is the amount of
time it takes for half of the
sample to decay into another
element
• The Red spheres are Uranium
238 molecules, which have a
½ life of 4.9 billion years.
Nuclear
Reactions
• Involve changes in the
nucleus
– Nuclear fusion, nuclear
fission
• New atoms appear as
products of the reaction.
• Breaks Dalton’s Law of
Conservation of Mass
• Large amount of energy
generated
– 1 million times more than
chemical reactions
– Nuclear fusion on the sun
– Nuclear fission for reactors
• Rate does not depend on
any physical properties
Show Me the Energy!!!
• Because nuclear reactions break Dalton’s Law
of Conservation of Mass, a very small amount of
mass is converted to energy.
• Einstein is credited with discovering the equation
to calculate the mass-energy defect.
E = mc2
E = change in energy (Joules)
M = change in mass (kilograms)
C = speed of light = 3x108 meters/second
• How Much Energy? The energy released from
the nuclear reaction of 1kg of uranium is
equivalent to the energy released during the
combustion of 4 billion kilograms of coal
1
9/18/2012
How to Use My Calculator!!
• Never type in “x10” into • Type in “3x108” into
your calculator!!
your calculator
• Your calculator either
– 3 EE 8
uses:
– 3 EXP 8
– EE
– EXP
– 10x
– 3 x10x
• Your calculator
should show:
• In some cases, the EE
or EXP may be on the
button or in a different
color ABOVE the
button
– 3 08
– 3E08
– 3 x10 8
• How would you write
it down?
Nuclear Fission
Decay vs. Nuclear Reactions
• Alpha, beta, and gamma
• Nuclear reactions involve
decay occur as ONE atom
more than just getting rid of
a few protons or neutrons.
tries to increase it’s
stability by getting rid of a
The new atoms produced
few neutrons, or protons &
are VERY different
neutrons.
elements than the reactant.
• The product is an alpha,
• Nuclear reactions must be
beta, or gamma particle
started, so there are 2
and ONE new atom.
things on the left hand side.
There is only ONE thing
– Nuclear fission: makes 2
on the left hand side.
or more much smaller
atoms
– Nuclear fusion: makes 1
much larger atom
Nuclear Fission
How is the above reaction different than a decay?
• Fission is where the nucleus breaks apart into 2 or
more much smaller nuclei.
1 large atom → 2 or more smaller atoms + ENERGY
• Heavy atoms (mass number>60) go through fission
to try to increase their stability.
• Like all nuclear reactions, nuclear fission releases a
large amount of energy.
Chain Reaction of Uranium-235
• The true power of
fission reactions
comes from a chain
reaction.
• A chain reaction is
where one fission
reaction can lead to
several more fission
reactions.
• Many, much smaller
atoms are made,
each one starting its’
own fission reaction.
• A chain reaction can only occur if the starting
material has enough mass to sustain a chain
reaction. This amount is called the critical mass.
• Nuclear Fission chain reactions are what occurs
in Nuclear Reactors and Atomic Bombs.
• The Nuclear reactor is a controlled fission
reaction, the bomb is not.
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9/18/2012
Nuclear Fusion
Nuclear Fusion
2 small atoms → 1 large atom + ENERGY
• The combining of 2 small atomic nuclei to form a
larger atom.
• Nuclear fusion occurs in the sun and generate
enough energy to power the solar system
• Fusion reactions release very large amount of
energy, but require extremely high temperatures
to start.
• Nuclear fusion is how all elements bigger than
Hydrogen, were made in stars.
1
4 1 H + 2 -10 e- 4
2
He + energy
Other Fusion Reactions
• Hydrogen Bomb or possible Fusion
nuclear reactor reaction
3H
1
+ 12H 4He
2
+ 10n
New Research Area is to create new
elements using fusion
• 20Ca + 95Am 115Uup
•
115Uup
113Uut
+ 42He
3