Unit Overview
Particle physics (AS)
CIE A-Level PhysicsΒ· 5 min read π n/a
1. Unit at a glance
This unit moves from a macroscopic view of matter to the microscopic structure of atoms and radiation. We start by breaking down the atom into its fundamental subatomic particles, then explore variations in atomic structure through isotopes. Next, we examine the three common types of ionizing radiation emitted by unstable nuclei, before covering the rules of spontaneous radioactive decay. The unit concludes by introducing the particle nature of light (photons), connecting particle physics to core quantum concepts.
Work through the following sub-topics in order to build your understanding:
Atomic structure
Learn the properties, relative masses and charges of the three core subatomic particles.
β β± 6 min
Isotopes
Understand isotopes and how to represent nuclides with proton and nucleon number notation.
β β± 4 min
Alpha, beta and gamma radiation
Compare ionizing power, penetration, range and deflection of the three main types of nuclear radiation.
β β β± 7 min
Radioactive decay
Balance nuclear decay equations and understand the spontaneous random nature of decay.
β β β± 6 min
Photons
Introduce the photon model of light, calculate photon energy and solve basic photon problems.
β β β β± 8 min
2. Common Pitfalls
Wrong move:
Confusing proton number (Z) with nucleon number (A) when calculating neutron count.
Why:
Z (lower subscript) is the number of protons, while A (upper superscript) is the total number of protons + neutrons.
Correct move:
Always calculate number of neutrons as , double-checking which number corresponds to which.
Wrong move:
Incorrectly balancing proton and nucleon numbers for beta decay.
Why:
Beta minus decay changes proton number but leaves total nucleon number unchanged, unlike alpha decay which reduces both.
Correct move:
Balance proton numbers and nucleon numbers separately on both sides of the decay equation to confirm they are equal.
3. Quick Reference Cheatsheet
Key Concept / Formula | Definition / Relationship |
|---|---|
Number of neutrons | , = nucleon number, = proton number |
Specific charge | Specific charge = , units: C kg |
Alpha decay general equation | |
Beta minus decay general equation | |
Photon energy | , J s |
What's Next
Start your study of this unit with the first sub-topic on atomic structure, where you will learn the fundamental properties of subatomic particles that underpin all topics in this unit. Work through each sub-topic in sequence to build your knowledge of radioactivity and the particle nature of light. Once you complete all topics here, you will be ready to progress to the next AS unit.