This topic has no equations on the equation sheet – it’s about understanding the atom and radioactivity. Each page has short notes, then questions to try on paper.
Key: C+S = Combined and Separate | S only = Separate Physics only | HT = Higher tier only
- Atoms, isotopes and the model of the atom (C+S)
- Radioactive decay and half-life (C+S)
- Hazards, uses, fission and fusion (S only)
Key definitions
Write your answer on paper first, then tap Show answer. Learn the key words – definition questions are quick marks in the exam.
1. What is the atomic number of an atom? (C+S)
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The number of protons in the nucleus. All atoms of the same element have the same atomic number.
2. What is the mass number of an atom? (C+S)
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The total number of protons and neutrons in the nucleus.
3. What are isotopes? (C+S)
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Atoms of the same element with the same number of protons but different numbers of neutrons.
4. What is an ion? (C+S)
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A charged atom. Atoms become positive ions when they lose one or more outer electrons.
5. What is radioactive decay? (C+S)
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The random process in which an unstable nucleus gives out radiation to become more stable.
6. What is activity, and what is its unit? (C+S)
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The rate at which a source of unstable nuclei decays. Unit: becquerel (Bq).
7. What is count-rate? (C+S)
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The number of decays recorded each second by a detector, such as a Geiger-Muller tube.
8. What is the half-life of a radioactive isotope? (C+S)
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The time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count-rate (or activity) to fall to half its initial level.
9. What is an alpha particle? (C+S)
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Two protons and two neutrons – the same as a helium nucleus.
10. What is a beta particle? (C+S)
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A high-speed electron ejected from the nucleus as a neutron turns into a proton.
11. What is a gamma ray? (C+S)
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Electromagnetic radiation emitted from the nucleus.
12. What does ionising mean? (C+S)
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Able to knock electrons off atoms, turning them into ions. Alpha is the most ionising, then beta, then gamma.
13. What is the difference between contamination and irradiation? (C+S)
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Contamination: the unwanted presence of materials containing radioactive atoms on or in other materials. Irradiation: the process of exposing an object to nuclear radiation – the object does not become radioactive.
14. What is background radiation? (S only)
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Radiation that is around us all the time, from natural sources (rocks, cosmic rays) and man-made sources (fallout from nuclear weapons testing and nuclear accidents).
15. What is nuclear fission? (S only)
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The splitting of a large, unstable nucleus (e.g. uranium or plutonium) into two smaller nuclei, releasing energy, two or three neutrons and gamma rays.
16. What is a chain reaction? (S only)
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When the neutrons released by one fission go on to cause further fissions, which release more neutrons, and so on.
17. What is nuclear fusion? (S only)
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The joining of two light nuclei to form a heavier nucleus. Some of the mass is converted into energy.
