Transcript Nuclear Fission and Fusion

05/04/2016
Nuclear Fission and
Fusion
L/O :- To know the process of nuclear fission
and fusion
05/04/2016
Nuclear fission an fusion
LO: To know the process of fission and fusion
Starter:
1) If a radioactive sample of rock started with 100
counts per second and 2 hours later has a count rate
of 25 counts per second, what is it’s half-life?
Try these questions, have a go at the answer
1) What do you think is meant by a ‘chain reaction?’
2) The gold that exists on our planet, where did it come
from? Was it made here or somewhere else?
3) How is a nuclear bomb similar to a nuclear reactor
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Nuclear reactors:
Remember that Nuclear
power stations make
electricity in a similar way
to fossil fuel power
stations.
Order these parts:
Generator, fossil fuel burner, turbine, steam boiler.
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The main difference is the burner.
Instead of a fuel being burnt, a nuclear reaction
generates heat.
This heat is then used to boil water which turns
a turbine which turns a generator to create
electricity.
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The main fuels used in nuclear reactors are:
Uranium - 235
And
Plutonium - 239
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Nuclear fission – the process
An atom of uranium or plutonium receives a neutron.
The neutron causes it to be unstable and undergo
nuclear fission.
The large atom will split into 2 smaller atoms, gamma
rays, kinetic energy and free neutrons.
What
do you
think the
neutrons
do?or
The free
neutrons
will free
join with
othermight
uranium
(thinkatoms
back to
to start
your starter!)
plutonium
a chain reaction
Nuclear fission
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More
neutrons
Neutron
Uranium or
plutonium
nucleus
Unstable
nucleus
New nuclei
(e.g. barium
and krypton)
Chain reactions
Each fission reaction releases
neutrons that are used in
further reactions.
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Controlling a chain reaction
To control a chain reaction, the spare
neutrons created after each atomic fission
need to be absorbed.
This can be done using control rods.
These are suspended above the nuclear
reactor. The more they are dipped into the
reactor the slower the reaction occurs.
(the rods are held by magnets in case of
emergency – why is this?)
Nuclear bombs
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How is a nuclear bomb like a nuclear reactor?
They both use the same fuel, they both use the
same process of having a uranium or plutonium
atom absorb a neutron which starts a chain
reaction.
So why doesn’t a reactor act like a bomb?
Fission summary
Fission uses uranium or plutonium
They first absorb a neutron.
It is the splitting of a larger nuclei into 2
smaller nuclei, energy and neutrons
The neutrons can go on and start a chain
reaction
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Nuclear Fusion
If fission is when large unstable atoms split up
and release energy,
Fusion is when atoms ‘fuse’ to become larger
ones.
It happens in stars. (We haven’t worked out
how to do it on earth YET!)
(nuclear fusion may well be the long term
answer to our planets fuel needs)
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That gold treasure!
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That gold treasure!
All the different elements found on earth were
once made in stars billions of years ago.
Long before our own sun was formed stars lived
and died in this part of the galaxy.
When a star explodes it can send its contents
scattering across millions of miles.
Our solar system is formed from the ‘debris’ or
‘left overs’ of these stars.
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So the gold?
So the gold that we treasure is made in
the heart of long dead stars.
Along with nearly every other element that
we have on earth.
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Deep within the sun,
Hydrogen atoms can fuse together
to form helium.
This releases huge amounts of
energy. (that’s why our sun is so hot)
As the hydrogen runs out the helium
nuclei will start to join releasing still
more energy.
Eventually, large atoms all the way up
to iron will be formed, when the star
may die and explode scattering its
contents.
Nuclear Fusion in stars
Proton
The heat of a supernova can
cause larger atoms to fuse
together into heavier elements.
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Neutron
In a star Hydrogen
atoms fuse
together to create
Helium atoms. This
is nuclear fusion
Fusion Summary
• Nuclear fusion is the joining of two
atomic nuclei to form a larger one.
• It is the main way that energy is
released in stars.
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