Alpha, beta and gamma radiation, half-life calculations, nuclear equations, fission and fusion — all of nuclear physics for GCSE.
Radioactivity and nuclear physics is one of the most concept-rich topics in GCSE Physics. It requires you to understand atomic structure at a deeper level, learn the properties of three different types of radiation, perform half-life calculations, write nuclear equations, and understand fission and fusion. This guide covers all of it clearly and precisely.
Some atomic nuclei are unstable — they have too many or too few neutrons relative to protons, making the nucleus energetically unfavourable. Unstable nuclei emit radiation spontaneously in order to become more stable. This process is called radioactive decay.
Radioactive decay is random and spontaneous — it cannot be predicted when any individual nucleus will decay, and it is not affected by temperature, pressure, chemical state or any other external factor. The rate of decay (activity) decreases over time as more nuclei decay and fewer unstable nuclei remain.
The most ionising radiation (alpha) is the least penetrating. The most penetrating (gamma) is the least ionising. This inverse relationship is tested directly — it occurs because alpha particles interact so strongly with matter that they lose energy very quickly and travel only short distances.
Nuclear equations show radioactive decay. Both mass number (top) and atomic number (bottom) must balance on both sides.
To complete a nuclear equation: find the missing mass number (top numbers must balance) and atomic number (bottom numbers must balance), then identify the element from the atomic number using the periodic table.
Half-life is the time taken for half the radioactive nuclei in a sample to decay, or equivalently, for the activity of the sample to halve. It is constant for any given isotope and cannot be changed by any physical or chemical process.
Start with the initial count/activity. Divide by 2 for each half-life that passes. Example: a sample has activity 800 Bq and half-life 3 years. After 3 years: 400 Bq. After 6 years: 200 Bq. After 9 years: 100 Bq. After 12 years: 50 Bq. If asked how many half-lives have passed: divide total time by half-life period. If asked the half-life from a graph: find the time for activity to halve from any starting point on the curve.
Fission is the splitting of a large, unstable nucleus into two smaller nuclei, releasing a large amount of energy and two or three neutrons. The released neutrons can trigger further fission events in other nuclei — a chain reaction. In a nuclear reactor, the chain reaction is controlled. In a nuclear bomb, it is uncontrolled.
Common fissile material: uranium-235 and plutonium-239. When a slow neutron is absorbed by U-235, the nucleus splits, releasing energy and 2–3 neutrons.
Fusion is the joining of two light nuclei to form a heavier nucleus, releasing a very large amount of energy. It is the process that powers stars — in the Sun, hydrogen nuclei fuse to form helium.
Fusion releases more energy per kilogram of fuel than fission and produces no long-lived radioactive waste. However, achieving fusion requires extremely high temperatures (millions of degrees) to overcome the electrostatic repulsion between positively charged nuclei. Sustained controlled fusion has not yet been achieved commercially — it remains one of the biggest challenges in physics.
The AQA radioactivity specification is at the AQA GCSE Physics specification page.
PaperPlus generates GCSE Physics radioactivity questions — radiation types, half-life, nuclear equations — for AQA, Edexcel and OCR. Completely free.
Start Practising Free →