A.2 Applications & Nuclear Energy
Exploring uses of radioisotopes in medicine and industry, nuclear fission, fusion, and the associated risks and benefits.
Questions to explore
- ? Can the energy inside an atom's nucleus solve our energy crisis?
- ? How do doctors use radioactivity to heal rather than harm?
💡 Key ideas, explained simply
🔨 Fission: splitting atoms
In nuclear fission a large nucleus (like uranium-235) absorbs a neutron and splits into two smaller nuclei, releasing energy plus 2–3 more neutrons. Those neutrons split more nuclei — a chain reaction. Control rods soak up spare neutrons to keep it steady in a reactor.
☀️ Fusion: joining atoms
In nuclear fusion two small nuclei (hydrogen isotopes) join to make a bigger one, releasing even more energy. This powers the Sun, but needs enormous temperature and pressure, which makes it very hard to sustain on Earth.
Fission vs fusion
| Feature | Fission | Fusion |
|---|---|---|
| What happens | Big nucleus splits | Small nuclei join |
| Fuel | Uranium, plutonium | Hydrogen isotopes |
| Where used | Nuclear power stations | The Sun and stars |
| Waste | Long-lived radioactive | Very little |
📖 Key terms
- Nuclear fission
- Splitting a large nucleus, releasing energy and neutrons.
- Nuclear fusion
- Joining small nuclei to form a larger one, releasing energy.
- Chain reaction
- Neutrons from one fission triggering further fissions.
- Control rod
- Absorbs neutrons to regulate a reactor.
- Radioactive tracer
- A radioisotope tracked through the body or a system.
- Radiotherapy
- Using gamma rays to destroy cancer cells.
✏️ Worked example
Evaluating nuclear power
Give one advantage and one disadvantage of generating electricity from nuclear fission (a common Criterion D "evaluate" task).
- 1
Advantage
Huge energy from little fuel, with almost no CO₂ emissions — helps fight climate change.
- 2
Disadvantage
Produces long-lived radioactive waste and carries a small risk of serious accidents.
A strong answer weighs both sides and reaches a justified conclusion.
🏥 Physics around you
Radioactivity heals as well as powers. Doctors inject short-half-life tracers to image organs, and aim gamma beams at tumours. The isotope is chosen carefully by its radiation type and half-life so it does its job then quickly fades.
🎯 Nail it in the exam
Fission, Fusion, and Chain Reactions
Fission: A heavy nucleus (e.g., uranium‑235) absorbs a neutron, becomes unstable, and splits into two smaller nuclei plus 2‑3 neutrons and energy. The neutrons go on to cause further fissions → chain reaction. Control rods absorb neutrons to regulate the reaction.
Fusion: Two light nuclei (e.g., hydrogen isotopes) combine at very high temperatures and pressures. This releases more energy than fission but is technically difficult to sustain on Earth.
Past papers often ask for the advantages and disadvantages of nuclear power (Criteria D).
-
In an ‘evaluate’ question, present both sides: reliable, low CO₂ vs radioactive waste, accidents, decommissioning costs.
-
Do not confuse chemical reactions with nuclear – nuclear changes the nucleus, chemical involves electrons only.
-
Diagrams of chain reactions must show neutrons splitting other nuclei.
Radioisotopes in Medicine and Industry
Radioactive sources are chosen based on half‑life and type of radiation.
Medical tracers: beta or gamma emitters with short half‑lives (hours) so they decay quickly after diagnosis. Iodine‑131 (beta/gamma, 8 days) is used for thyroid scans.
Radiotherapy: gamma rays (e.g., cobalt‑60) focused on tumours to kill cancer cells.
Industrial tracers: gamma sources to detect leaks in pipes; half‑life must be long enough for the process.
Thickness monitoring: beta particles – amount transmitted indicates paper thickness.
Always link the choice of isotope to its properties (penetrating power, half‑life).
-
Alpha sources are not used inside the body because they are too ionising and cannot penetrate tissue to be detected externally.
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When ‘justifying’ an isotope choice, use data: half‑life, decay type.
-
For ‘suggest’ questions, think about safety: short half‑life reduces exposure time, penetrating radiation can be detected outside the body.
🧠 Check your understanding
Tap an answer to see if you're right — and why.
Q1. Which process powers the Sun?
Q2. Why is a radioactive tracer used in medicine?
📝 Exam-style questions
Try each one, then reveal the model answer.