Nuclear Reactions Fission and Fusion. CS 4.4 CS 4.5 State that in fission a nucleus of large mass...
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Transcript of Nuclear Reactions Fission and Fusion. CS 4.4 CS 4.5 State that in fission a nucleus of large mass...
CS 4.4
CS 4.5
State that in fission a nucleus of large mass splits into 2 nuclei of smaller mass numbers, usually with the release of neutrons.
State that fission may be spontaneous or induced by neutron bombardment.
CS 4.6
CS 4.7
CS 4.8
State that in fusion, 2 nuclei combine to form a nucleus of larger mass number.
Explain, using E = mc2, how the products of fission and fusion acquire large amounts of kinetic energy.
Carry out calculations using E = mc2 for fission and fusion reactions.
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.
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.
Induced Fission
Nuclear fission can be induced by bombarding atoms with neutrons.
Induced fission decays are also accompanied by the release of neutrons.
The nuclei of the atoms then split into 2 equal parts.
U23692
The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron.
The Fission Process
The uranium-236 nucleus formed is very unstable.
The Fission Process
It transforms into an elongated shape for a short time.
The uranium-236 nucleus formed is very unstable.
The Fission Process
It transforms into an elongated shape for a short time.
The uranium-236 nucleus formed is very unstable.
The Fission Process
It transforms into an elongated shape for a short time.
It then splits into 2 fission fragments and releases neutrons.
The Fission Process
14156Ba
9236Kr
n 1 0
n 1 0
n 1 0
It then splits into 2 fission fragments and releases neutrons.
The Fission Process
14156Ba
9236Kr
n 1 0
n 1 0
n 1 0
It then splits into 2 fission fragments and releases neutrons.
The Fission Process
14156Ba
9236Kr
n 1 0
n 1 0
n 1 0
It then splits into 2 fission fragments and releases neutrons.
The Fission Process
14156Ba
9236Kr
n 1 0
n 1 0
n 1 0
Nuclear Fission Examples
U235
92 +Ba141
56+ n1
03n
1
0 +Kr 92
36
U235
92 +Cs138
55+ n1
02n
1
0 +Rb 96
37
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 << EK after fission
Energy is being released as a result of the fission reaction.
Energy from Fission
U235
92 +Cs138
55+ n1
02n
1
0 +Rb 96
37
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
Energy from Fission
Calculate the total mass before and after fission takes place.
The total mass before fission (LHS of the equation):
The total mass after fission (RHS of the equation):
3.9014 x 10-25 + 1.6750 x 10-27 = 3.91815 x 10-25 kg
2.2895 x 10-25 + 1.5925 x 10-25 + (2 x 1.6750 x 10-27) = 3.9155 x 10-25 kg
Energy from Fission
The total mass before fission =
The total mass after fission =
3.91815 x 10-25 kg
3.91550 x 10-25 kg
total mass before fission > total mass after fission
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.
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)
E
m c2
Energy from Fission
E = mc2
U235
92 +Cs138
55+ n1
02n1
0 +Rb 96
37
Calculate the energy released from the following fission reaction:
m = 2.65 x 10-28 kg c = 3 x 108 ms-1
E = E
E = 2.65 x 10-28 x (3 x 108)2
E = 2.385 x 10-11 J
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.
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
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
Nuclear Fusion
In nuclear fusion, two nuclei with low mass numbers combine to produce a single nucleus with a higher mass number.
H 2
1 +He 4
2+ n1
0H
3
1 +Energy
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
H 2
1 +He 4
2+ n1
0H
3
1 +Energy
Energy from Fusion
Calculate the following:
• The mass difference.
• The energy released per fusion.
Energy from Fusion
The total mass before fusion (LHS of the equation):
The total mass after fission (RHS of the equation):
3.345 x 10-27 + 5.008 x 10-27 = 8.353 x 10-27 kg
6.647 x 10-27 + 1.675 x 10-27 = 8.322 x 10-27 kg
H 2
1 +He 4
2+ n1
0H
3
1 +Energy
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