Nuclear Reactions

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Nuclear Reactions

• Fission and Fusion

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CS 4.4
State that in fission a nucleus of large mass
splits into 2 nuclei of smaller mass numbers,
usually with the release of neutrons.
CS 4.5
State that fission may be spontaneous or induced
by neutron bombardment.
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CS 4.6
State that in fusion, 2 nuclei combine to form a
nucleus of larger mass number.
CS 4.7
Explain, using E mc2, how the products of
fission and fusion acquire large amounts of
kinetic energy.
CS 4.8
Carry out calculations using E mc2 for fission
and fusion reactions.
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Fission
When atoms are bombarded with neutrons, their
nuclei splits into 2 parts which are roughly
equal in size.
Nuclear fission in the process whereby a nucleus,
with a high mass number, splits into 2 nuclei
which have roughly equal smaller mass numbers.
During nuclear fission, neutrons are released.
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Nuclear Fission
There are 2 types of fission that exist
1. Spontaneous Fission
2. Induced Fission
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Spontaneous Fission
Some radioisotopes contain nuclei which are
highly unstable and decay spontaneously by
splitting into 2 smaller nuclei.
Such spontaneous decays are accompanied by the
release of neutrons.
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Induced Fission
Nuclear fission can be induced by bombarding
atoms with neutrons.
The nuclei of the atoms then split into 2 equal
parts.
Induced fission decays are also accompanied by
the release of neutrons.
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The Fission Process
A neutron travels at high speed towards a
uranium-235 nucleus.
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The Fission Process
A neutron travels at high speed towards a
uranium-235 nucleus.
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The Fission Process
A neutron travels at high speed towards a
uranium-235 nucleus.
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The Fission Process
The neutron strikes the nucleus which then
captures the neutron.
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The Fission Process
The nucleus changes from being uranium-235 to
uranium-236 as it has captured a neutron.
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The Fission Process
The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short
time.
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The Fission Process
The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short
time.
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The Fission Process
The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short
time.
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The Fission Process
It then splits into 2 fission fragments and
releases neutrons.
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The Fission Process
It then splits into 2 fission fragments and
releases neutrons.
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The Fission Process
It then splits into 2 fission fragments and
releases neutrons.
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The Fission Process
It then splits into 2 fission fragments and
releases neutrons.
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Nuclear Fission Examples
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Energy from Fission
Both the fission fragments and neutrons travel at
high speed.
The kinetic energy of the products of fission are
far greater than that of the bombarding neutron
and target atom.
EK before fission ltlt EK after fission
Energy is being released as a result of the
fission reaction.
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Energy from Fission
Element Atomic Mass (kg)
23592U 3.9014 x 10-25
13855Cs 2.2895 x 10-25
9637Rb 1.5925 x 10-25
10n 1.6750 x 10-27
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Energy from Fission
Calculate the total mass before and after fission
takes place.
The total mass before fission (LHS of the
equation)
3.9014 x 10-25 1.6750 x 10-27 3.91815 x 10-25
kg
The total mass after fission (RHS of the
equation)
2.2895 x 10-25 1.5925 x 10-25 (2 x 1.6750 x
10-27) 3.9155 x 10-25 kg
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Energy from Fission
The total mass before fission
3.91815 x 10-25 kg
3.91550 x 10-25 kg
The total mass after fission
total mass before fission gt total mass after
fission
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Energy from Fission
mass difference, m total mass before fission
total mass after fission
m 3.91815 x 10-25 3.91550 x 10-25
m 2.65 x 10-28 kg
This reduction in mass results in the release of
energy.
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Energy Released
The energy released can be calculated using the
equation
E mc2
Where
E energy released (J)
m mass difference (kg)
c speed of light in a vacuum (3 x 108 ms-1)
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Energy from Fission
Calculate the energy released from the following
fission reaction
m 2.65 x 10-28 kg
E mc2
E 2.65 x 10-28 x (3 x 108)2
c 3 x 108 ms-1
E 2.385 x 10-11 J
E E
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Energy from Fission
The energy released from this fission reaction
does not seem a lot.
This is because it is produced from the fission
of a single nucleus.
Large amounts of energy are released when a large
number of nuclei undergo fission reactions.
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Energy from Fission
Each uranium-235 atom has a mass of 3.9014 x
10-25 kg.
The total number of atoms in 1 kg of uranium-235
can be found as follows
No. of atoms in 1 kg of uranium-235 1/3.9014 x
10-25
No. of atoms in 1 kg of uranium-235 2.56 x 1024
atoms
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Energy from Fission
If one uranium-235 atom undergoes a fission
reaction and releases 2.385 x 10-11 J of energy,
then the amount of energy released by 1 kg of
uranium-235 can be calculated as follows
total energy energy per fission x number of
atoms
total energy 2.385 x 10-11 x 2.56 x 1024
total energy 6.1056 x 1013 J
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Nuclear Fusion
In nuclear fusion, two nuclei with low mass
numbers combine to produce a single nucleus with
a higher mass number.
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The Fusion Process
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The Fusion Process
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The Fusion Process
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The Fusion Process
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The Fusion Process
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The Fusion Process
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The Fusion Process
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The Fusion Process
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The Fusion Process
ENERGY
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The Fusion Process
ENERGY
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The Fusion Process
ENERGY
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The Fusion Process
ENERGY
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Energy from Fusion
Element Atomic Mass (kg)
21H 3.345 x 10-27
31H 5.008 x 10-27
42He 6.647 x 10-27
10n 1.6750 x 10-27
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Energy from Fusion
Calculate the following

• The mass difference.

• The energy released per fusion.

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Energy from Fusion
The total mass before fusion (LHS of the
equation)
3.345 x 10-27 5.008 x 10-27 8.353 x 10-27 kg
The total mass after fission (RHS of the
equation)
6.647 x 10-27 1.675 x 10-27 8.322 x 10-27 kg
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Energy from Fusion
m total mass before fission total mass after
fission
m 8.353 x 10-27 8.322 x 10-27
m 3.1 x 10-29 kg
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Energy from Fusion
m 3.1 x 10-29 kg
E mc2
E 3.1 x 10-29 x (3 x 108)2
c 3 x 108 ms-1
E 2.79 x 10-12 J
E E
The energy released per fusion is 2.79 x 10-12 J.