Edexcel International GCSE Physics Section 7: Radioactivity and Particles Exam Questions

About Edexcel International GCSE Physics Section 7: Radioactivity and Particles

Section 7 of Edexcel International GCSE Physics covers the structure of the atom, radioactive decay and nuclear energy. You describe atoms and isotopes using nuclide notation, the properties of alpha, beta, gamma and neutron radiation, and how to balance nuclear equations. The section covers background radiation, measuring activity with a Geiger-Muller detector, half-life calculations and graphs, and the uses and dangers of radiation, including contamination and irradiation. The final part deals with nuclear fission of uranium-235 in a reactor, chain reactions, control rods and moderators, and nuclear fusion in stars. Examiners commonly test half-life, nuclear equations and the role of each part of a reactor.

What you need to know

• Atoms and isotopes An atom has a nucleus of protons and neutrons surrounded by electrons. Isotopes of an element have the same atomic number but different mass numbers. Use nuclide notation with mass number on top and atomic number below.
• Types of radiation Alpha: helium nucleus, strongly ionising, stopped by paper. Beta: fast electron from the nucleus, stopped by a few mm of aluminium. Gamma: electromagnetic radiation, weakly ionising, reduced by thick lead or concrete. Neutrons can also be emitted.
• Nuclear equations Alpha decay reduces mass number by 4 and atomic number by 2. Beta decay leaves mass number the same and increases atomic number by 1. Gamma emission does not change either number.
• Half-life and activity Activity is measured in becquerels using a Geiger-Muller detector, subtracting background count. Half-life is the time for half the undecayed nuclei, or the activity, to halve.
• Uses and hazards Uses include medical tracers, radiotherapy, sterilisation, thickness gauges and smoke alarms. Contamination involves radioactive material getting on or in something; irradiation is exposure to radiation from outside.
• Nuclear fission A uranium-235 nucleus absorbs a slow neutron and splits into two daughter nuclei, releasing two or three neutrons and kinetic energy. The moderator slows neutrons; control rods absorb neutrons to control the chain reaction.
• Nuclear fusion Two light nuclei join to form a heavier nucleus, releasing energy. Fusion is the energy source of stars; it needs very high temperatures and pressures to overcome the electrostatic repulsion between nuclei.

Common mistakes in Section 7: Radioactivity and Particles

• Saying the moderator absorbs neutrons. The moderator slows them down; control rods absorb them.
• Forgetting to subtract background count before working out half-life from data.
• Saying an irradiated object becomes radioactive. It does not; contamination is the problem because the source stays on or in the object.
• Saying gamma radiation is the most ionising. Alpha is the most ionising; gamma is the most penetrating.
• Mixing up fission and fusion. Fission splits a large nucleus; fusion joins small nuclei.

Try three Section 7: Radioactivity and Particles exam-style questions