4.7 - fission and fusion reactions
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Syllabus pointsNeutron‐induced nuclear fission is a reaction in which a
heavy nuclide captures a neutron and then splits into smaller radioactive nuclides with the release of energy
A fission chain reaction is a self‐sustaining process that may be controlled to produce thermal energy, or uncontrolled to release energy explosively if its critical mass is exceeded
Nuclear fusion is a reaction in which light nuclides combine to form a heavier nuclide, with the release of energy
More energy is released per nucleon in nuclear fusion than in nuclear fission because a greater percentage of the mass is transformed into energy
Learning goals Define:
Fission Neutron-induced fission Chain reaction Critical mass
Recall that fission is only possible for two isotopes, Uranium-235 and Plutonium-239
Describe the fission process Describe how the velocity of incoming neutrons can affect the fission
process Compare and contrast controlled and uncontrolled fission reactions Define:
Fusion
Describe the fusion process Explain why the fusion process releases more energy (per nucleon) than
the fission process Compare and contrast energy emission from a fission reaction, fusion
reaction and decay processes
What is Fission? NUCLEAR FISSION occurs when an atomic nucleus
splits into two or more pieces. This is often triggered by the absorption of a neutron. – HP p. 180
Example 1Identify the unknown quantities (A, Z, X, Y) in the fission reactions below.
a) 01𝑛 + 92
235𝑈 → 𝑍𝐴𝑋 + 38
93𝑆𝑟 + 201𝑛
b) 01𝑛 + 92
235𝑈 → 𝑍88𝑋 + 54
𝐴𝑌 + 1201𝑛
c) 01𝑛 + 92
235𝑈 → 3587𝐵𝑟 + 𝑍
143𝐿𝑎 + 𝑥01𝑛
d) 01𝑛 + 92
235𝑈 → 𝑍𝐴𝑋 + 36
92𝐾𝑟 + 301𝑛
Example 1Identify the unknown quantities (A, Z, X, Y) in the fission reactions below.
a) 01𝑛 + 92
235𝑈 → 54141𝑋𝑒 + 38
93𝑆𝑟 + 201𝑛
b) 01𝑛 + 92
235𝑈 → 3888𝑆𝑟 + 54
136𝑋𝑒 + 1201𝑛
c) 01𝑛 + 92
235𝑈 → 3587𝐵𝑟 + 57
143𝐿𝑎 + 601𝑛
d) 01𝑛 + 92
235𝑈 → 56141𝐵𝑎 + 36
92𝐾𝑟 + 301𝑛
Example 2
A typical fission reaction can be seen below:
01𝑛 + 92
235𝑈 → 56141𝐵𝑎 + 36
92𝐾𝑟 + 301𝑛
If there is a loss of mass of 0.215 u calculate how much energy is released from this fission reaction.
Example 2
A typical fission reaction can be seen below:
01𝑛 + 92
235𝑈 → 56141𝐵𝑎 + 36
92𝐾𝑟 + 301𝑛
If there is a loss of mass of 0.215 u calculate how much energy is released from this fission reaction.
Example 3
Calculate the amount of energy released by the fission reaction shown below:
01𝑛 + 92
235𝑈 → 54141𝑋𝑒 + 38
93𝑆𝑟 + 201𝑛
Isotope Mass (u)
Uranium-235 235.043930
Xenon-141 140.92665
Strontium-93 92.914026
Example 3
Calculate the amount of energy released by the fission reaction shown below:
01𝑛 + 92
235𝑈 → 54141𝑋𝑒 + 38
93𝑆𝑟 + 201𝑛
Isotope Mass (u)
Uranium-235 235.043930
Xenon-141 140.92665
Strontium-93 92.914026
Example 4
mass of neutron = 1.674 95 × 10–27 kg,mass of Uranium-235 = 3.903 05 × 10–25 kg,mass of Barium-144 = 2.389 92 × 10–25 kgmass of Krypton-89 =1.476 53 × 10–25 kg
a What is the decrease in the mass of the nuclear particles involved in this fission reaction?b How many joules of energy are released during the fission of this uranium-235 nucleus?c Express the decrease in mass as a percentage of the mass of the initial nuclear particles. d If a 5 kg lump of pure uranium-235 completely underwent fission, how much energy (in joules) would be released?
Example 5
If you build a Nuclear reactor using Uranium 235 (previous slide), how many fission reactions per second are required to power Dr Pusey’s PlayStation 4 (110 Watts)?
ResourcesAV
Tyler DeWitt – Nuclear Fission (8:59)
Crash Course – Nuclear Chemistry (part 2): Fission and fusion (11:18) – Following this slide!
Bang Goes the Theory – Inside a nuclear reactor core (3:52)
ANSTO – OPAL research reactor animation (3:55)
Harvard Lecture Demonstrations – Mousetrap Fission (2:27)
Simulation
Nuclear Fission – pHet simulation
From: http://nuclear.duke-energy.com/2013/01/30/fission-vs-fusion-whats-the-difference/
Example 1Identify the unknown quantities (A, Z, X, Y) in the fusion reactions below.
a) 𝑍2𝐻 + 𝑍
3𝐻 → 𝑍𝐴𝑋 + 0
1𝑛
b) 12𝐻 + 1
𝐴𝐻 → 𝑍3𝑋 + 0
1𝑛
c) 12𝑋 + 2
3𝑌 → 𝑍4𝐻𝑒 + 𝑍
𝐴𝐻
Example 1Identify the unknown quantities (A, Z, X, Y) in the fusion reactions below.
a) 12𝐻 + 1
3𝐻 → 24𝐻𝑒 + 0
1𝑛
b) 12𝐻 + 1
2𝐻 → 23𝐻𝑒 + 0
1𝑛
c) 12𝐻 + 2
3𝐻𝑒 → 24𝐻𝑒 + 2
1𝐻
Example 2
Calculate the amount of energy released by the fusion reaction shown below:
12𝐻 + 1
3𝐻 → 24𝐻𝑒 + 0
1𝑛
Isotope Mass (u)
Deuterium (Hydrogen-2) 2.014101
Tritium (Hydrogen-3) 3.016049
Helium-4 4.002602
Example 2
Calculate the amount of energy released by the fusion reaction shown below:
12𝐻 + 1
3𝐻 → 24𝐻𝑒 + 0
1𝑛
Isotope Mass (u)
Deuterium (Hydrogen-2) 2.014101
Tritium (Hydrogen-3) 3.016049
Helium-4 4.002602
ResourcesAV
PhD Comics – What is fusion, video and simulation (7:56)
Further Reading
Scientific American - Fusion Experiment Breakthrough
How did you go? Define:
Fission
Neutron-induced fission
Chain reaction
Critical mass
Recall that fission is only possible for two isotopes, Uranium-235 and Plutonium-239
Describe the fission process
Describe how the velocity of incoming neutrons can affect the fission process
Compare and contrast controlled and uncontrolled fission reactions
Define:
Fusion
Describe the fusion process
Explain why the fusion process releases more energy (per nucleon) than the fission process
Compare and contrast energy emission from a fission reaction, fusion reaction and decay processes
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