IGCSE Physics Three Types of Nuclear Emission Questions and Worked Solutions
50 topic-wise practice questions on The Three Types of Nuclear Emission (Unit 5: Nuclear Physics), written to the Cambridge IGCSE Physics 0625 syllabus for 2026–2028, each with a step-by-step worked solution.
Topic guide: The Three Types of Nuclear Emission
Unstable nuclei emit alpha particles, beta particles or gamma radiation. The three emissions differ in nature, ionising ability and penetrating power. Emission is spontaneous and random.
Key formulas
| α = ⁴₂He, β = ⁰₋₁e, γ = EM wave | nature of the emissions | Core |
Prerequisite knowledge
- Nucleus and charges (5.1)
- EM spectrum (3.3)
Exam tips & common mistakes
- Ionising and penetrating abilities are in opposite orders
- Use absorber tests (paper, aluminium, lead) to identify radiation
- β⁺ is not on the syllabus — β means β⁻
Key facts from the syllabus (5.2.2)
- Emission is spontaneous and random in direction
- Alpha: helium nucleus (2p + 2n), most ionising, least penetrating — stopped by paper or a few cm of air
- Beta: high-speed electron, moderately ionising — stopped by a few mm of aluminium
- Gamma: electromagnetic radiation, least ionising, most penetrating — reduced by thick lead or concrete
- Extended in electric and magnetic fields, alpha and beta are deflected in opposite directions; beta much more (lower mass); gamma undeflected
- Extended alpha is most ionising because of its large charge and kinetic energy
Textbook: §5.2 Radioactivity, pp. 260–274
Describe the emission of radiation from a nucleus in terms of timing and direction.
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Method: Spontaneous, random.
State the nature of an alpha particle.
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Method: Helium nucleus.
State the nature of a beta particle.
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Method: Fast electron.
State the nature of gamma radiation.
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Method: EM wave.
State which radiation is the most ionising.
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Method: Alpha.
State which radiation is the most penetrating.
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Method: Gamma.
State what is needed to stop alpha particles.
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Method: Paper.
State what is needed to stop beta particles.
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Method: Aluminium.
State what reduces gamma radiation significantly.
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Method: Lead.
A source's count rate is unchanged by paper, falls a lot with 3 mm aluminium, but is not zero. State the radiations emitted.
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Method: No alpha; beta stopped; remainder gamma.
Arrange alpha, beta and gamma in order of increasing ionising ability.
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Method: Gamma least.
Explain why alpha sources are dangerous inside the body but less so outside.
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Method: Highly ionising but stopped by skin.
State the composition of an alpha particle.
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Method: 2p + 2n.
State the charge on a beta particle.
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Method: −1.
State the charge on gamma radiation.
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Method: 0.
State the range of alpha particles in air.
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Method: Few cm.
Arrange α, β, γ in order of increasing penetrating power.
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Method: α least.
A source's count rate drops to background when paper is inserted. State the radiation and explain.
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Method: Paper stops α.
A source's count rate is unchanged by 5 mm of aluminium but falls with thick lead. State the radiation.
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Method: Penetrates Al.
A source's count rate falls a little with paper and to background with 5 mm aluminium. State the radiations.
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Method: α and β.
Explain why gamma radiation is used to treat deep tumours.
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Method: Penetrating.
State what is meant by ionising radiation.
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Method: Removes electrons.
State the approximate thickness of lead needed to significantly reduce gamma radiation.
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Method: Several cm.
Describe the deflection of alpha and beta particles in an electric field.
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Method: Opposite directions.
State the deflection of gamma radiation in an electric or magnetic field.
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Method: Uncharged.
Explain why beta particles are deflected more than alpha particles in a magnetic field.
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Method: Much smaller mass.
Explain why alpha particles are highly ionising.
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Method: Large charge and KE.
Explain why gamma radiation is weakly ionising.
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Method: No charge.
Explain why alpha particles have a short range in air.
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Method: Lose energy quickly.
State the relative charge of alpha and beta particles.
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Method: +2 and −1.
Alpha, beta and gamma pass between two charged plates. Describe what is seen.
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Method: Three paths.
Explain why beta particles are less ionising than alpha particles.
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Method: Smaller charge, less KE.
State the direction of deflection of beta particles between charged plates.
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Method: Towards +.
State the direction of deflection of alpha particles between charged plates.
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Method: Towards −.
Explain why alpha particles are deflected less than beta particles in an electric field, though they have a larger charge.
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Method: Much larger mass.
Alpha particles move right through a magnetic field pointing into the page. State the deflection direction.
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Method: Left-hand rule, current right.
Beta particles move right through a magnetic field pointing into the page. State the deflection direction.
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Method: Current left.
Explain why gamma rays pass through an electric field undeflected.
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Method: No charge.
Explain how the kinetic energy of radiation affects its ionising ability.
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Method: More energy, more ions.
Explain why gamma rays are the most penetrating radiation.
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Method: Few interactions.
Challenge questions
Harder, multi-step questions at the top end of the exam. Attempt these once you are confident with the questions above.
Describe the nature, relative ionising effect and penetrating ability of alpha, beta and gamma radiation.
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Method: Table.
A source is tested: no change with paper; count falls from 300 to 160 counts/min with 3 mm aluminium; falls to near background with 5 cm lead. Identify the emissions.
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Method: Penetration.
Explain why the most ionising radiation is the least penetrating.
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Method: Loses energy fast.
Describe how you would use absorbers and a GM tube to show that a source emits only beta radiation.
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Method: Absorber test.
Explain the relative ionising effects of alpha and beta in terms of charge and kinetic energy.
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Method: Charge and KE.
A mixed α, β, γ beam passes between two charged plates (top positive). Describe the path of each and explain the size of the deflections.
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Method: Charge and mass.
Beta particles enter a magnetic field directed into the page while moving to the right. State the direction of the deflection and explain using Fleming's left-hand rule.
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Method: Current to the left.
Explain why alpha particles are deflected in a magnetic field less than beta particles despite having twice the charge.
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Method: Mass.
Explain why gamma radiation passes undeflected through both electric and magnetic fields.
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Method: No charge.
Explain why alpha emitters are dangerous if swallowed but relatively safe outside the body, using ionisation and penetration.
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Method: Range.
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