Atoms, nuclei and radiation
Cambridge A-Level Physics (9702) · Unit 11: Particle physics · 14 flashcards
Atoms, nuclei and radiation is topic 11.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 11 — Particle physics , alongside Fundamental particles. In one line: The nuclear model consists of a central nucleus containing protons and neutrons, surrounded by orbiting electrons. The nucleus contains almost all the mass of the atom.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 14 flashcards — 11 definitions, 2 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 11 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Describe the simple nuclear model of the atom
The nuclear model consists of a central nucleus containing protons and neutrons, surrounded by orbiting electrons. The nucleus contains almost all the mass of the atom.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Infer from the α-particle scattering results that atoms contain a nucleus and that this nucleus is very small.
- Describe a simple nuclear model of the atom made up of protons, neutrons and orbiting electrons.
- Distinguish between proton number and nucleon number.
- Understand that isotopes are versions of one element whose nuclei contain different numbers of neutrons.
- Understand and use the standard nuclide notation, where the symbol X carries the nucleon number A at top left and the proton number Z at bottom left.
- Understand that in nuclear processes both charge and nucleon number are conserved.
- Describe what α-, β- and γ-radiations are made of, and their mass and charge, covering both β⁻ (electrons) and β⁺ (positrons).
- Understand that an antiparticle matches its corresponding particle in mass but has the opposite charge, and that the positron is the electron's antiparticle.
- State that β⁻ decay produces (electron) antineutrinos, while β⁺ decay produces (electron) neutrinos.
- Understand that α-particles are emitted with discrete energies, whereas β-particles show a continuous spread of energies, since β-decay also emits (anti)neutrinos.
- Represent α-decay and β-decay with a radioactive decay equation in the form ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂α.
- Express and work with masses in unified atomic mass units (u).
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Atoms, nuclei and radiation
- › When describing scattering experiments, use precise terms like 'very large proportion' for undeflected particles and 'very small proportion' for large-angle deflections.
- › Recall that in β+ decay, a proton changes into a neutron and emits a positron and a neutrino.
- › Recall that in beta-minus decay, an electron and an antineutrino are emitted; ensure nucleon and proton numbers balance precisely.
- › Recall that an alpha particle consists of two protons and two neutrons; its charge is always +2e.
What did the α-particle scattering experiment reveal about the atom's structure?
The experiment showed that the atom contains a tiny, dense, positively charged nucleus. This refuted the plum pudding model and suggested most of the atom is empty space.
Describe the simple nuclear model of the atom.
The nuclear model consists of a central nucleus containing protons and neutrons, surrounded by orbiting electrons. The nucleus contains almost all the mass of the atom.
Distinguish between nucleon number (A) and proton number (Z).
Nucleon number (A) is the total number of protons and neutrons in the nucleus. Proton number (Z) is the number of protons in the nucleus, which defines the element.
What are isotopes?
Isotopes are forms of the same element that have the same number of protons but different numbers of neutrons in their nuclei.
Explain the notation A Z X for representing nuclides.
A Z X represents a nuclide where X is the element symbol, A is the nucleon number (mass number), and Z is the proton number (atomic number).
State the conservation laws applicable to nuclear processes.
In nuclear processes, both nucleon number (A) and charge (Z) are conserved. The total number of nucleons and the total charge before and after the process remain constant.
Describe the composition, mass, and charge of α-radiation.
α-radiation consists of helium nuclei (2 protons and 2 neutrons). It has a mass of approximately 4u and a charge of +2e (where e is the elementary charge).
Describe the composition, mass, and charge of β-radiation.
β-radiation consists of either electrons (β⁻) or positrons (β⁺). Both have a mass close to 0u and charges of -e (β⁻) or +e (β⁺), respectively.
Describe the composition, mass, and charge of γ-radiation.
γ-radiation consists of high-energy photons. It has zero mass and zero charge.
What is an antiparticle, and what is the antiparticle of an electron?
An antiparticle has the same mass as its corresponding particle but opposite charge. The antiparticle of an electron is a positron.
What particles are emitted during β⁻ and β⁺ decay?
During β⁻ decay, an electron and an antineutrino are emitted. During β⁺ decay, a positron and a neutrino are emitted.
Explain why α-particles have discrete energies, while β-particles have a continuous range of energies.
α-particles have discrete energies because the energy released in α-decay is fixed. β-particles have a continuous range of energies because the energy is shared with the (anti)neutrino also emitted in β-decay.
Represent the alpha decay of Uranium-238.
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Define the unified atomic mass unit (u).
The unified atomic mass unit (u) is defined as 1/12 of the mass of a neutral carbon-12 atom. It is approximately equal to 1.66 x 10⁻²⁷ kg.
Review the material
Read full revision notes on Atoms, nuclei and radiation — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 11 — Particle physics
Atoms, nuclei and radiation sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Atoms, nuclei and radiation deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Atoms, nuclei and radiation deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Rate each card Hard, Okay, or Easy after flipping.