What types of nuclear radiation are there, and how do they differ?
Radioactive decay and nuclear radiation: the nature of alpha, beta and gamma radiation and neutron emission, their penetrating and ionising powers, and decay equations.
A focused answer to AQA GCSE Physics 4.4.2, covering radioactive decay as a random process, the nature of alpha, beta, gamma and neutron radiation, their relative ionising and penetrating powers, and how to balance nuclear decay equations.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
AQA wants you to describe radioactive decay as a random process, give the nature and properties of alpha, beta and gamma radiation (and neutron emission), compare their ionising and penetrating powers, and balance nuclear decay equations. This is part of topic 4.4.2 of the AQA GCSE Physics (8463) specification.
Radioactive decay
The types of radiation
The more ionising a radiation is, the less penetrating it tends to be, because it transfers its energy more quickly. Ionisation means knocking electrons off atoms in the material the radiation passes through, turning them into ions. A heavy, doubly charged alpha particle interacts strongly with the electrons it passes, so it produces a dense trail of ionisation and quickly runs out of energy, which is why it stops after a few centimetres of air. A gamma photon has no charge and interacts only weakly, so it can travel a long way while ionising very little, which is why it is so penetrating. Beta sits between the two. This ranking has practical consequences: outside the body, gamma and beta are the more hazardous because they reach living tissue, but if a source is swallowed or inhaled, alpha becomes the most dangerous because it deposits all its energy in a small region of tissue.
These properties also determine real uses. Alpha sources are used in smoke detectors, where the short range means the radiation does not escape the device. Beta is used to monitor and control the thickness of materials such as paper or foil, because the amount passing through depends sensitively on thickness. Gamma is used to sterilise medical equipment and to treat cancer, because it penetrates deep into the body or through packaging.
Decay equations
Try this
Q1. State the nature and penetrating power of alpha radiation. [2 marks]
- Cue. A helium nucleus (2 protons and 2 neutrons); stopped by paper or a few centimetres of air.
Q2. A nucleus emits a beta particle. State the change in its mass number and atomic number. [2 marks]
- Cue. Mass number unchanged; atomic number increases by .
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20206 marksCompare alpha, beta and gamma radiation in terms of their nature, their ionising power and their penetrating power.Show worked answer →
A top-band level-of-response answer covers all three radiations on all three points. Nature: alpha is a helium nucleus (2 protons and 2 neutrons), beta is a fast-moving electron emitted from the nucleus when a neutron changes into a proton, and gamma is a high-frequency electromagnetic wave with no charge or mass. Ionising power: alpha is the most strongly ionising, beta is moderate, gamma is the least ionising. Penetrating power: alpha is the least penetrating (stopped by paper or a few centimetres of air), beta is more penetrating (stopped by a few millimetres of aluminium), and gamma is the most penetrating (needs thick lead or concrete). The key linking idea, worth credit, is that the more strongly ionising a radiation is, the less penetrating it is, because it gives up its energy more quickly. Markers reward a structured comparison covering each radiation on each property.
AQA 20184 marksA radium nucleus has a mass number of and an atomic number of . It decays by emitting an alpha particle to form radon. Calculate the mass number and atomic number of the radon nucleus produced, and state how these would change if the original nucleus had instead emitted a beta particle.Show worked answer →
For alpha decay the mass number decreases by and the atomic number decreases by . So mass number becomes (1 mark) and atomic number becomes (1 mark), which is radon. For beta decay instead, the mass number would be unchanged at because a beta particle (an electron) has negligible mass (1 mark), while the atomic number would increase by to because a neutron changes into a proton (1 mark). Markers reward correct application of both decay rules and the reasoning that beta emission leaves the nucleon count unchanged.
Related dot points
- The structure of the atom: the sizes and charges of protons, neutrons and electrons, the nuclear model, and how the model developed from the plum pudding model.
A focused answer to AQA GCSE Physics 4.4.1, covering the relative sizes and charges of protons, neutrons and electrons, the nuclear model of the atom, and how the alpha scattering experiment replaced the plum pudding model.
- Isotopes and ions: atomic number and mass number, how isotopes differ, how ions form, and the standard nuclear notation.
A focused answer to AQA GCSE Physics 4.4.1, covering atomic number and mass number, how to read nuclear notation, what makes atoms isotopes of an element, and how atoms become positive or negative ions.
- Half-life: the meaning of half-life, calculating activity after a number of half-lives, and the difference between contamination and irradiation.
A focused answer to AQA GCSE Physics 4.4.2, covering the meaning of half-life, how to calculate the remaining activity or number of nuclei after several half-lives, and the difference between radioactive contamination and irradiation.
- Nuclear fission and fusion: the process of fission and the chain reaction, the process of fusion, and how each releases energy (separate physics only).
A focused answer to AQA GCSE Physics 4.4.3, covering nuclear fission as the splitting of a large unstable nucleus, the chain reaction in a reactor, nuclear fusion as the joining of light nuclei in stars, and how each process releases energy.
Sources & how we know this
- AQA GCSE Physics (8463) specification — AQA (2016)