Theme E — Nuclear and Quantum Physics
E.4 Fission — IB Physics SL Revision Notes & Topical Questions
5 min read 8 parts Lesson 16 of 30 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
E.4 Fission — IB PHYSICS SL notes: Summarise how nuclear fission releases energy, how a chain reaction is controlled in a reactor and how the waste is managed.Nuclear fission = the splitting of a large unstable nucleus into two smaller nuclei.Uranium and plutonium isotopes are us…
- A neutron strikes the nucleus
- Spontaneous fission is rare
- Uranium-235 absorbs a slow neutron to form uranium-236
- The mass defect between parent and daughters appears as energy
- Energy transfers from the nuclear potential store to the kinetic energy of the fragments
- Neutrons released by one fission can trigger further fissions
Section 1 of 8The fission process
1Nuclear fission
Nuclear fission the splitting of a large unstable nucleus into two smaller nuclei.
- Uranium and plutonium isotopes are used as fuels in power stations.
2A neutron strikes the nucleus
- A neutron strikes the nucleus it splits into two daughter nuclei, two or three neutrons and gamma rays.
3Spontaneous fission is rare
- Spontaneous fission is rare it happens without added energy; induced fission needs an absorbed neutron.
4Uranium-235 absorbs a slow neutron to form uranium-236
- Uranium-235 absorbs a slow neutron to form uranium-236 which splits almost immediately.
Section 2 of 8Energy release
1
The daughter nuclei have a higher binding energy per nucleon than the parent.
2The mass defect between parent and daughters appears as energy
- The mass defect between parent and daughters appears as energy about 200 MeV per fission of uranium-235.
3
Energy transfers from the nuclear potential store to the kinetic energy of the fragments
- and is then carried away as heat.
4
Fission fuel has the highest energy density of any fuel currently available.
Section 3 of 8Chain reaction and critical mass
1Neutrons released by one fission can trigger further fissions
- Neutrons released by one fission can trigger further fissions this is a chain reaction.
2Only thermal (slow) neutrons induce fission
- Only thermal (slow) neutrons induce fission faster neutrons rebound from the uranium-235 nucleus.
3Controlled reaction
- Controlled reaction exactly one neutron from each fission causes another fission.
4Critical mass
Critical mass the minimum mass of fuel that maintains a steady chain reaction.
- Below critical mass (subcritical) the reaction dies away.
- Above critical mass (supercritical) the reaction runs away and may explode.
Section 4 of 8Reactor components
| Component | Purpose |
|---|---|
| Control rods | Absorb neutrons; lowering them slows fission, raising them speeds it |
| Moderator | Slows fast neutrons to thermal speeds |
| Heat exchanger | Transfers thermal energy from the coolant to water making steam |
| Shielding | Steel and concrete wall absorbs radiation from the core |
- Steam from the heat exchanger drives turbines
- the turbines drive generators.
Section 5 of 8Waste and safety
Waste is low-, intermediate- or high-level
- Waste is low-, intermediate- or high-level depending on its activity and half-life.
High-level waste is vitrified, sealed in containers and stored deep underground
- High-level waste is vitrified, sealed in containers and stored deep underground after cooling in ponds.
Advantages of nuclear power
- Advantages of nuclear power no greenhouse gases in operation, high energy density and large fuel reserves.
Disadvantages
- Disadvantages long-lived waste, risk of accidents such as Chernobyl, possible misuse and mining hazards.
Section 6 of 8More from the specification
1Deep geological storage over years
- Deep geological storage over years vitrified high-level radioactive actinide waste requires secure subterranean isolation lasting hundreds of thousands of years.
2Radioactive
- Describes a nucleus that decays spontaneously and randomly.
3Efficiency
- Useful output divided by total input.
4Specific energy
- Energy released per unit mass of a fuel, in J kg−1
5Radioactive waste
- Unwanted material that emits ionising radiation.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Nuclear fission | Splitting of a heavy nucleus into two smaller nuclei with release of energy. |
| Chain reaction | Fissions caused by neutrons released in earlier fissions. |
| Critical mass | Minimum fuel mass needed to sustain a chain reaction. |
| Moderator | Material that slows fast neutrons by collisions. |
| Control rod | Neutron-absorbing rod used to regulate the fission rate. |
| Thermal neutron | Slow neutron in thermal equilibrium with its surroundings. |
Section 8 of 8Exam technique
1
Thinking fission is alpha decay — fission splits the nucleus into two comparable pieces.
2
Saying control rods slow the neutrons — they absorb them.
3
Using more than critical mass in a reactor — that gives a runaway reaction.
4
Forgetting that fission products stay radioactive for a long time.
Marked practiceQuizzes for this lesson
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