What is inside the atom, what are the three types of radiation, and what does half-life mean?
The nuclear model of the atom and isotopes, radioactive decay as random and spontaneous, the three types of radiation alpha, beta and gamma with their properties, half-life and decay curves, and the uses and dangers of radioactivity.
A focused CCEA GCSE Single Award Science answer on atomic and nuclear physics, covering the nuclear model and isotopes, radioactive decay, the three types of radiation alpha, beta and gamma, half-life and decay curves, and the uses and dangers of radioactivity.
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What this dot point is asking
CCEA wants you to describe the nuclear model of the atom and isotopes, explain that decay is random and spontaneous, give the properties of alpha, beta and gamma radiation, define and use half-life, and state the uses and dangers of radioactivity.
The nuclear model and isotopes
Radioactive decay
The three types of radiation
The more ionising a radiation, the more cell damage it does but the shorter its range.
Half-life
To find the activity after a whole number of half-lives, halve the starting value once for each half-life.
There is also a low level of background radiation around us all the time, from natural sources such as rocks (especially radon gas), cosmic rays from space and food and drink, plus small man-made sources such as medical X-rays. When measuring a source's activity you should subtract this background count to get the true reading.
Examples in context
Example 1. Why a smoke alarm uses an alpha source. A smoke alarm contains a weak alpha source. The alpha radiation ionises the air, letting a small current flow; smoke absorbs the alpha and disrupts the current, setting off the alarm. Alpha is ideal because it is stopped by a few centimetres of air, so it cannot escape the alarm to harm anyone, yet it ionises the air strongly. This links the properties of alpha to a real device.
Example 2. Choosing a medical tracer. A medical tracer must give out radiation that leaves the body to be detected, so a gamma emitter is used, and it must have a short half-life so the patient is not exposed for long. Matching the type of radiation and the half-life to the job is exactly the reasoning CCEA rewards in uses-of-radiation questions, and it shows why alpha would be a poor choice for a tracer.
Try this
Q1. Which type of radiation is a helium nucleus? [1 mark]
- Cue. Alpha radiation.
Q2. A source has a half-life of 2 hours and starts at 800 Bq. What is its activity after 4 hours? [2 marks]
- Cue. Two half-lives: 800 to 400 to 200 Bq.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA SAS 20214 marksCompare the penetrating power of alpha, beta and gamma radiation, and state what stops each one.Show worked answer →
Four marks for the order and what stops each.
Alpha is the least penetrating; it is stopped by paper or a few centimetres of air.
Beta is moderately penetrating; it is stopped by a few millimetres of aluminium.
Gamma is the most penetrating; it is only reduced by thick lead or concrete.
Alpha is the most ionising and gamma the least, so the more penetrating a radiation, the less ionising it is. Markers reward the order of penetration and the correct absorber for each.
CCEA SAS 20193 marksA radioactive source has an activity of 1600 Bq and a half-life of 5 days. Calculate its activity after 20 days.Show worked answer →
Three marks for the number of half-lives, the halving and the answer.
Number of half-lives equals 20 divided by 5, which is 4 half-lives.
Halve the activity four times: 1600 to 800 to 400 to 200 to 100.
So the activity after 20 days is 100 Bq.
Markers reward the correct number of half-lives, halving the right number of times, and the final value with the unit becquerels.
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Sources & how we know this
- CCEA GCSE Science: Single Award specification — CCEA (2017)