Nuclear Physics — Class 10 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 10 Science, Physics — Chapter 6. Inside the nucleus: radioactivity, fission, fusion and their uses.
1. About this chapter
This chapter explores the nucleus, radioactivity and its three radiations, the energy of nuclear fission and fusion, the working idea of a nuclear reactor, useful radioisotopes, and the biological effects and safety of radiation.
2. Radioactivity
- Radioactivity: the spontaneous emission of radiation from unstable nuclei (discovered by Henri Becquerel).
- Three types of radiation:
| Radiation | Nature | Charge | Penetrating power | Ionising power |
|---|---|---|---|---|
| Alpha (α) | helium nucleus | +2 | low (stopped by paper) | high |
| Beta (β) | fast electron | −1 | medium (stopped by aluminium) | medium |
| Gamma (γ) | EM radiation | 0 | very high (stopped by thick lead) | low |
- Natural radioactivity occurs in heavy elements (e.g. uranium, radium); artificial (induced) radioactivity is produced by bombarding nuclei.
3. Fission and fusion
- Nuclear fission: a heavy nucleus (e.g. U-235) splits into lighter nuclei, releasing huge energy and neutrons → a chain reaction. Used in nuclear reactors and atom bombs.
- Nuclear fusion: light nuclei (e.g. hydrogen) combine to form a heavier nucleus, releasing even more energy. It powers the Sun and stars.
4. Nuclear reactor and applications
- A nuclear reactor controls fission to generate electricity. Key parts: fuel (U-235), moderator (slows neutrons), control rods (absorb neutrons), and coolant.
- Applications of radioisotopes: medicine (cancer treatment, tracers), agriculture (mutation breeding), industry (flaw detection), and carbon dating of fossils.
- Units: activity in becquerel (Bq) or curie (Ci).
5. Biological effects and safety
- Radiation can damage living cells and cause burns, mutations or cancer.
- Safety measures: lead shielding, lead aprons, remote handling, dosimeters, and safe disposal of nuclear waste. Background radiation is the low-level natural radiation around us.
6. Common mistakes
- Mistake: Saying gamma rays have the highest ionising power. Fix: Gamma has the highest penetration but the lowest ionising power; alpha is the opposite.
- Mistake: Confusing fission and fusion. Fix: Fission = splitting a heavy nucleus; fusion = joining light nuclei (Sun's energy).
- Mistake: Calling beta a helium nucleus. Fix: Beta is a fast electron; alpha is a helium nucleus.
7. Practice (book-back style)
- Define radioactivity and name its discoverer.
- Compare alpha, beta and gamma radiations (charge and penetration).
- Differentiate nuclear fission and fusion.
- Name the parts of a nuclear reactor.
- Give two applications of radioisotopes and two safety measures.
8. Answer key
- Spontaneous emission of radiation by unstable nuclei; discovered by Henri Becquerel.
- α: +2, low penetration; β: −1, medium; γ: 0, very high penetration.
- Fission: a heavy nucleus splits releasing energy; Fusion: light nuclei combine releasing energy (powers the Sun).
- Fuel, moderator, control rods and coolant.
- Applications: cancer therapy, carbon dating (also tracers, breeding). Safety: lead shielding, dosimeters (also remote handling, safe waste disposal).
9. Quick revision
- Physics Ch 6 · radioactivity, α/β/γ, fission, fusion, reactor.
- α = He nucleus (+2, low penetration, high ionising); β = electron (−1); γ = EM wave (0, high penetration).
- Fission splits heavy nuclei (reactor); fusion joins light nuclei (Sun).
- Reactor: fuel, moderator, control rods, coolant.
- Radioisotopes: medicine, agriculture, carbon dating; handle with shielding.
