FUSION AND FISSION
THE SUN
Nuclear Fusion
• Nuclear fusion is the process by
which multiple nuclei join together to
form a heavier nucleus.
• It is accompanied by the release or
absorption of energy depending on
the masses of the nuclei involved..
FUSION
NEUTRON
DEUTERIUM
HELIUM
TRITIUM
http://fusioned.gat.com
Nuclear Fusion
• Iron and nickel nuclei have the largest
binding energies per nucleon of all nuclei
and therefore are the most stable.
Nuclear Fusion
• The fusion of two nuclei lighter than iron or
nickel generally releases energy.
• The fusion of nuclei heavier than them
absorbs energy.
Complete the Reaction
1H
element
atomic number
(protons)
4Be
1H
6C
2He
1H
2He
1H
2He
6C
4Be
2He
8
2He
O
Energy needed for Fusion
The thermal activity of a gas is described by its
temperature measurement which is really an
indication of its velocity/energy.
Thermal energy is represented by the height that the
upper magnet.
The upper ring has a potential energy given by PE = mgh
at its drop point which is converted into kinetic energy
(KE = 1/2 mv2)
As the magnet falls towards the lower magnet. The two
magnets click lightly when the kinetic energy is just
greater than the magnetic energy that holds them
apart.
Since Kinetic Energy = Potential Energy (ignoring
frictional components), the gravitational pull and mass
of the upper magnet are constant, then the height
needed to overcome the magnetic repelling force is
proportional to that magnetic repelling force.
Energy needed for Fusion
PE =mg x h2-h1
PE = KE = Fxh1
F=force of repulsion
F=PE/h1
Upper Drop
Position
Ring
Magnets
Float
Position
Lower
Magnet
Wood Block
h2
h1
Fusion Changes Mass to Energy
E=mc2
.993 kg Helium
1kg Hydrogen
Cookie Fusion
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Procedure
Cut 2 squares of wax paper 10 cm on a side
Cut 5 cm wide slice of cookie dough (atom)
Find the mass of the atom and record on the table
Place the atom one cm away from the edge of a wax
paper square
Repeat step 2 thru 4 for a second atom
Place the atoms about 2 cm from each other
Place both atoms on a plate and microwave for 1 minute
Remove the “new element” and let cool for 2 minutes
Find the mass of the “new element”
Complete the table
Cookie Fusion
Mass Before
Cooking
Atom 1
Atom 2
Total
Difference
Mass After
Cooking
Learning Check
What process creates energy in the Sun?
Fusion of hydrogen into helium in the Sun’s core
generates the Sun’s energy.
How long ago did fusion generate the
energy we now receive as sunlight?
Fusion created the energy we receive today about a
million years ago. This is the time it takes for photons
and then convection to transport energy through the
solar interior to the photosphere. Once sunlight
emerges from the photosphere, it takes only about 8
minutes to reach Earth.
Learning Check
NUCLEAR FISSION
A reaction in which an atomic
nucleus of a radioactive element
splits by bombardment from an
external source, with
simultaneous release of large
amounts of energy, used for
electric power generation
Nuclear Fission
Neutron induced in U235
Fission is Exothermic
The sum of the masses of
the resulting nuclei is less
than the original mass
(about 0.1% less)
The “missing mass” is converted
to energy according to E=mc2
Neutrons may:
1 - Cause another fission by colliding with a U235 nucleus
• Creates two smaller nuclides and free neutrons
• The free neutrons potentially collide with nearby U235 nuclei
• May cause the nuclide to split as well
Each split (fission) is
accompanied by a large
quantity of E-N-E-R-G-Y
2 - Be absorbed in other material
3 - Lost in the system
If sufficient neutrons are present, we may achieve a chain reaction
U.S. Electrical Power
Production by Source
Source: EIA
(2004)
Nuclear Fuel Costs
• Nuclear Fuel Costs Include
–
–
–
–
Uranium
Enrichment
Manufacturing
Waste Disposal
• Total Nuclear Fuel Cost is Only About 0.5 cents
per kilowatt-hour
– Uranium accounts for only about 20% of this cost or
0.1 cents per kilowatt-hour
– Increasing Uranium Cost has Minimal Impact
Review
Nuclear fission:
A large nucleus splits into several
small nuclei when impacted by a
neutron, and energy is released in
this process
Nuclear fusion:
Several small nuclei fuse
together and release
energy.
Draw a Double Bubble Map of
Fusion and Fission
fission
fusion
Differences
Similarities
Differences