# Nuclear and particle physics

> Rutherford scattering, nuclear radius, radioactive decay and half-life, mass–energy equivalence, fission and fusion, and the quark model of hadrons.

Canonical: https://revise-gray.vercel.app/library?topic=wjec-alevel-physics.nuclear
Last updated: 2026-08-01

Flagship subject: topics and specification statements are authored to the WJEC specification. No question in it has been through human review yet.

- Subject: [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- Specification reference: Unit 4.3–4.5
- Difficulty: 4/5
- Assessment objectives: AO1, AO2
- Status: authored · checked · 2026-08-01

## Specification coverage

| Reference | Statement | AOs |
| --- | --- | --- |
| Unit 4.3(a) | describe Rutherford scattering evidence for the nuclear atom | AO1 |
| Unit 4.3(b) | relate nuclear radius to nucleon number by r proportional to A to one third | AO2 |
| Unit 4.4(a) | define activity decay constant half-life and use A equals lambda N and N equals N0 exp minus lambda t | AO2 |
| Unit 4.4(b) | use mass-energy equivalence delta E equals delta m c squared for binding energy | AO2 |
| Unit 4.4(c) | explain binding energy per nucleon curve and energy release in fission and fusion | AO1, AO2 |
| Unit 4.5(a) | classify hadrons as baryons or mesons in the quark model and apply conservation laws | AO1, AO2 |
| Unit 4.5(b) | describe neutron to proton beta minus decay with emission of electron and antineutrino | AO1 |

## Summary

Rutherford scattering, nuclear radius, radioactive decay and half-life, mass–energy equivalence, fission and fusion, and the quark model of hadrons.

## What earns marks

- Activity A = λN and N = N₀e^(−λt), with half-life t½ = ln2/λ.
- ΔE = Δmc²; binding energy per nucleon peaks near iron-56, which is why both fission and fusion can release energy.
- Baryons are three quarks, mesons a quark–antiquark pair; charge, baryon number and lepton number are conserved.
- β⁻ decay converts a neutron into a proton, emitting an electron and an antineutrino.

## Where marks are lost

- Using half-life in the exponential formula without converting to the decay constant.
- Forgetting the antineutrino in β⁻ decay and breaking lepton-number conservation.
- Confusing binding energy with binding energy per nucleon when comparing nuclei.

## Related

- [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- [Nuclear and particle physics lesson](https://revise-gray.vercel.app/lesson?subject=wjec-alevel-physics&topic=wjec-alevel-physics.nuclear)