What is radioactivity, and how do we describe nuclear decay and half-life?
The structure of the atom and isotopes, the types of nuclear radiation (alpha, beta and gamma), nuclear decay equations, half-life, and the dangers and uses of radioactivity.
A focused answer to Edexcel GCSE Combined Science Topic 6 (CP6), covering atomic structure and isotopes, the types of nuclear radiation, nuclear decay, half-life, and the dangers and uses of radioactivity.
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What this dot point is asking
Edexcel wants you to describe atomic structure and isotopes, describe alpha, beta and gamma radiation and their properties, write simple nuclear decay descriptions, define and use half-life, and outline the dangers and uses of radioactivity.
Atomic structure and isotopes
Radioactive decay is a random process: you cannot predict when a particular nucleus will decay, only the rate for a large number.
Types of nuclear radiation
The more ionising a radiation, the more damage it does over a short range; the more penetrating, the further it travels through materials.
Half-life
Dangers and uses
Radiation is dangerous because it ionises atoms and can damage or kill cells, and high doses can cause cancer or radiation sickness. Exposure is reduced by shielding, distance and limiting time. Radiation is also useful: gamma rays sterilise equipment and treat cancer, beta sources are used in thickness gauges, alpha sources are used in some smoke detectors, and isotopes are used as medical tracers and to date rocks and ancient remains.
The choice of radiation for a use depends on its properties. A medical tracer uses a gamma (or beta) source with a short half-life, so it can be detected outside the body but does not stay radioactive for long. A thickness gauge for paper or foil uses a beta source, because beta is partly absorbed by the material: if the material gets thicker, less beta gets through, and the gauge adjusts the rollers. A smoke detector uses an alpha source, because alpha is stopped by smoke particles, which sets off the alarm.
Two ways of being exposed are worth distinguishing. Irradiation is being exposed to a source from outside; it stops as soon as the source is removed or shielded. Contamination is getting radioactive atoms onto or into the body, which is more serious because the source stays with you and keeps emitting radiation. Alpha sources are especially hazardous if swallowed or inhaled, because all their ionising energy is deposited inside the body, even though they are harmless outside the skin.
Try this
Q1. State what an alpha particle is made of. [1 mark]
- Cue. Two protons and two neutrons (a helium nucleus).
Q2. Define half-life. [1 mark]
- Cue. The time for half the radioactive nuclei (or the activity) to decay.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20204 marksCompare alpha, beta and gamma radiation in terms of what they are made of and their penetrating power.Show worked answer →
A 4-mark compare question on the three radiations.
An alpha particle is two protons and two neutrons (a helium nucleus); it is the most ionising but the least penetrating, stopped by paper or skin (1 mark). A beta particle is a fast-moving electron from the nucleus; it is moderately ionising and penetrating, stopped by a few millimetres of aluminium (1 mark). Gamma is a high-energy electromagnetic wave; it is the least ionising but the most penetrating, needing thick lead or concrete to reduce it (2 marks).
Markers reward what each radiation is and a correct penetrating-power order: alpha (paper), beta (aluminium), gamma (lead/concrete).
Edexcel 20224 marksA radioactive isotope has a half-life of 5 days. A sample has an activity of . Calculate its activity after 15 days, showing your working.Show worked answer →
A 4-mark half-life calculation.
15 days is three half-lives () (1 mark). After each half-life the activity halves: after 5 days it is , after 10 days , after 15 days (3 marks).
Markers reward finding the number of half-lives and halving the activity that many times to reach 100 Bq. A table or step-by-step halving is the clearest method.
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Sources & how we know this
- Edexcel GCSE (9-1) Combined Science (1SC0) specification — Pearson (2016)