5.2.2Nuclear Physics
THE Three Types OF Nuclear Emission — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 11 parts Lesson 11 of 17 1 quiz
Curriculum Equation Key Radioactive Decay & Half-Life FormulasFast Exam Solution
N(t) = N₀ × (1/2)t / t½ | λ = ln(2) / t½ ≈ 0.693 / t½ | E = Δm × c²
Lesson summary
5.2.2 The Three Types of Nuclear Emission — IGCSE PHYSICS notes: Describe alpha, beta and gamma emissions in terms of nature, charge, ionising effect and penetration, and their deflection in fields.Random — emissions occur randomly over space and time from unstable nuclei.Three t…
- Ionisation
- Electric field
- Magnetic field
- Linked to charge and kinetic energy
- Alpha particle
- Beta particle
Part 1 of 9Radioactive emission
Radioactive emission
Random
- Random emissions occur randomly over space and time from unstable nuclei.
Three types
- Three types alpha, beta and gamma radiation can be emitted.
Ionisation
- Ionisation the removal (or addition) of electrons from atoms to make ions.
- Ionising radiation damages living cells.
Part 2 of 9Alpha (α)
Nature
- Nature a helium nucleus of 2 protons and 2 neutrons, 42He, with charge +2.
Ionising
- Ionising the most strongly ionising.
Penetration
- Penetration the least penetrating, stopped by a sheet of paper or a few cm of air.
Part 3 of 9Beta (β−)
Nature
- Nature a fast-moving electron emitted from the nucleus, with charge −1.
Ionising
- Ionising moderately ionising.
Penetration
- Penetration stopped by a few mm of aluminium, with a range of roughly a metre in air.
Part 4 of 9Gamma (γ)
Nature
- Nature high-frequency electromagnetic radiation with no charge and no mass.
Ionising
- Ionising the least ionising.
Penetration
- Penetration the most penetrating, reduced by thick lead or concrete.
Part 5 of 9Comparison
| Property | Alpha | Beta | Gamma |
|---|---|---|---|
| Nature | Helium nucleus | Electron | Electromagnetic wave |
| Charge | +2 | −1 | 0 |
| Ionising | Strongly | Moderately | Weakly |
| Stopped by | Paper | Aluminium | Thick lead (reduced) |
| Magnetic field | Deflected slightly | Deflected strongly, opposite way | Not deflected |
Part 6 of 9Deflection in fields (Extended)
Electric field
- Electric field alpha is deflected towards the negative plate, beta towards the positive plate and gamma is undeflected.
Magnetic field
- Magnetic field alpha and beta are deflected in opposite directions and gamma is undeflected.
- Use Fleming's left-hand rule, remembering that the current for beta is opposite to its motion.
Amount
- Amount beta is deflected much more than alpha because it has a much smaller mass.
Part 7 of 9Ionising power (Extended)
Ionising power (Extended)
Linked to charge and kinetic energy
- Linked to charge and kinetic energy alpha has a large charge and is slow and heavy, so it interacts with many atoms and loses its energy quickly.
Result
- Result it is strongly ionising and poorly penetrating.
Gamma
- Gamma it is uncharged, so it interacts with few atoms and penetrates far.
Part 8 of 9Identifying radiation using absorbers
1
Measure the background count rate and subtract it from all later readings.
2
Measure the count rate with no absorber, with the source close to the detector.
3
Place paper between the source and detector: a large drop shows alpha.
4
Replace with a few mm of aluminium: a further drop shows beta.
5
Replace with thick lead: any count remaining before this shows gamma.
6
Conclude which emissions are present.
Part 9 of 9More from the specification
More from the specification
Differential penetration as an identification means
- Differential penetration as an identification means testing attenuation through paper, aluminium,
- or lead absorbers provides a clear experimental means to distinguish radiation types.
Alpha particles
- Helium nuclei of two protons and two neutrons, strongly ionising, stopped by paper and a few centimetres of air.
Beta particles
- Fast electrons emitted when a neutron changes into a proton, moderately ionising and stopped by a few millimetres of aluminium.
Gamma radiation
- Electromagnetic waves from the nucleus, weakly ionising and very penetrating, reduced only by thick lead or concrete.
Radioactive decay and half-life
- Decay is random and spontaneous, and the half-life is the time for the activity or number of undecayed nuclei in a sample to halve.
Isotopes and nuclear equations
- Isotopes of an element have the same atomic number but different mass numbers,
- and decay equations balance both the nucleon number and the charge.
Alpha particle
- Helium nucleus, charge +2.
Penetrating power
- How far radiation travels through a material.
Ionising power
- How strongly radiation ionises atoms.
Decay equation
- An equation in nuclide notation with balanced nucleon and proton numbers.
Radioactive
- Describes a nucleus that decays spontaneously and randomly.
Half-life
- Time for half the nuclei of an isotope to decay.
Isotope
- Atom of the same element with a different number of neutrons.
Activity
- Number of decays per second of a sample.
Key terms
| Term | Meaning |
|---|---|
| Alpha particle | Helium nucleus, charge +2. |
| Beta particle | Fast electron, charge −1. |
| Gamma ray | High-frequency electromagnetic wave with no charge. |
| Ionisation | Removing or adding electrons to make ions. |
| Absorber | Material placed between source and detector to identify the radiation. |
Avoid these mistakes
1
Saying the most ionising radiation is the most penetrating — it is the least penetrating.
2
Saying alpha and beta curve the same way in a field — they curve in opposite directions.
3
Forgetting to subtract the background count.
4
Saying gamma is deflected by a magnetic field — it has no charge.
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