What are alpha, beta and gamma radiation, and how do they differ?
Radioactive decay, the properties of alpha, beta and gamma radiation, their penetrating power, and the dangers and uses of radiation.
A focused answer to the WJEC GCSE Science Double Award Unit 6 topic on radiation, covering radioactive decay, the properties and penetrating power of alpha, beta and gamma radiation, and the dangers and uses of radiation.
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What this dot point is asking
WJEC Double Award Unit 6 wants you to describe radioactive decay, the properties and penetrating power of alpha, beta and gamma radiation, and the dangers and uses of radiation.
Radioactive decay
The activity of a source is the number of decays per second; it falls over time as the unstable nuclei decay.
The three types of radiation
So the order of penetrating power is gamma > beta > alpha, and the order of ionising power is the reverse: alpha > beta > gamma.
Why penetrating power matters
The penetrating power decides how each type is used and how dangerous it is. Alpha cannot pass through skin, so it is most dangerous inside the body (where it ionises cells strongly). Gamma passes through the body easily, so it can be used for imaging and is dangerous from outside. Knowing what stops each type lets you choose the right one for a job and the right shielding.
Dangers and uses of radiation
Radiation is ionising, so it can damage or kill cells and cause cancer or mutations; exposure is kept as low as possible, and shielding (such as lead) is used. But radiation is also very useful:
- Gamma rays: sterilising medical equipment, treating cancer, and tracing the flow inside the body (medical tracers).
- Beta: thickness control in manufacturing (such as paper or foil).
- Alpha: in some smoke detectors.
Background radiation
We are all exposed to a low level of background radiation all the time, which comes from natural and human-made sources. Natural sources include radon gas from rocks and soil, cosmic rays from space, and radioactive substances in food and the ground. Human-made sources include medical X-rays and a small amount from nuclear power and weapons testing. When measuring a radioactive source, scientists first measure the background count and subtract it from their readings, so the measurement is of the source alone. Knowing what background radiation is, and that it must be subtracted, is a common practical point.
Staying safe with radiation
Because radiation is ionising and can damage cells, people who work with it must reduce their exposure. This is done by keeping a distance from the source (intensity falls with distance), reducing the time spent near it, and using shielding such as lead aprons or thick walls. Radioactive sources are stored in lead-lined containers and handled with tongs, not bare hands. Being able to suggest ways to reduce the dose - distance, time and shielding - is a common safety question, and it links to the penetrating powers of the different types of radiation.
Try this
Q1. What stops beta radiation? [1 mark]
- Cue. A few millimetres of aluminium.
Q2. What is an alpha particle? [1 mark]
- Cue. A helium nucleus (2 protons and 2 neutrons).
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksDescribe the penetrating power of alpha, beta and gamma radiation, naming what stops each.Show worked answer →
A Unit 6 describe question worth 4 marks. Reward: alpha is the least penetrating, stopped by a sheet of paper (or a few cm of air) (1); beta is more penetrating, stopped by a few millimetres of aluminium (1); gamma is the most penetrating, only reduced by thick lead or concrete (1); so the order of penetrating power is gamma > beta > alpha (1). Markers credit paper for alpha, aluminium for beta and lead/concrete for gamma. A common error is to swap alpha and gamma.
WJEC style3 marksWhat is radioactive decay, and why is it described as a random process?Show worked answer →
A Unit 6 explain question. Reward: radioactive decay is when an unstable nucleus breaks down and emits radiation (alpha, beta or gamma) (1); it is random because you cannot predict which nucleus will decay or when a particular nucleus will decay (1); you can only say how likely it is, or how the count rate falls on average (1). Markers credit the unstable nucleus emitting radiation, and the unpredictability of which/when. A common error is to say decay happens at a fixed, predictable time for each atom.
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