Edexcel IGCSE Physics Radioactivity questions

Radioactivity syllabus

Questions on radioactivity can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

• 7.2 describe the structure of an atom in terms of protons, neutrons and electrons and use symbols such as ¹⁴₆C to describe particular nuclei
• 7.3 know the terms atomic (proton) number, mass (nucleon) number and isotope
• 7.4 know that alpha (α) particles, beta (β−) particles, and gamma (γ) rays are ionising radiations emitted from unstable nuclei in a random process
• 7.5 describe the nature of alpha (α) particles, beta (β−) particles and gamma (γ) rays, and recall that they may be distinguished in terms of penetrating power and ability to ionise
• 7.6 practical: investigate the penetration powers of different types of radiation using either radioactive sources or simulations
• 7.7 describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the four main types of radiation (alpha, beta, gamma and neutron radiation)
• 7.8 understand how to balance nuclear equations in terms of mass and charge
• 7.9 know that photographic film or a Geiger−Müller detector can detect ionising radiations
• 7.10 explain the sources of background (ionising) radiation from Earth and space
• 7.11 know that the activity of a radioactive source decreases over a period of time and is measured in becquerels
• 7.12 know the definition of the term 'half-life' and understand that it is different for different radioactive isotopes
• 7.13 use the concept of the half-life to carry out simple calculations on activity, including graphical methods
• 7.14 describe uses of radioactivity in industry and medicine
• 7.15 describe the difference between contamination and irradiation
• 7.16 describe the dangers of ionising radiations, including: that radiation can cause mutations in living organisms that radiation can damage cells and tissue the problems arising from the disposal of radioactive waste and how the associated risks can be reduced

How to answer radioactivity questions

1. Track mass number and atomic number separately when completing nuclear equations.
2. Compare radiation using both ionising ability and penetrating power.
3. For half-life, repeat the same halving interval and keep the starting quantity clear.
4. Distinguish irradiation from contamination and connect each risk reduction to the exposure route.

Radioactivity example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Working With Graphs

Question 1

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6 A teacher shows his class how to investigate the half-life of a radioactive source.

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Every half a minute, the teacher records the count rate.

He corrects for background radiation and produces this results table.

Time in minutes	Corrected count rate in Bq
0	49
0.5	30
1.0	24
1.5	18
2.0	15
2.5	11
3.0	10
3.5	9
4.0	5
4.5	6

Draw a graph of corrected count rate against time for these results.

Final answer

Plot corrected count rate against time and draw one smooth curve through the points:

Mark scheme points

1. M1 Use suitable, even scales that cover all the results on both axes.
2. M2 Label both axes with the correct quantity and unit: time in minutes and corrected count rate in Bq.
3. M3 Plot the data points at their correct coordinates.
4. M4 Include the complete set of results, including the final points at 4.0 min and 4.5 min.
5. M5 Draw one single smooth curve through the plotted points.

Explanation

Time is the independent variable, so it is placed on the horizontal axis. Corrected count rate is placed on the vertical axis. A linear scale from 0 to 5.0 min and from 0 to 50 Bq uses the graph space well and includes every value.

Plot each ordered pair from the table, such as (0 min, 49 Bq), (0.5 min, 30 Bq), and (4.5 min, 6 Bq). The count rate generally decreases, but the final value rises slightly from 5 Bq at 4.0 min to 6 Bq at 4.5 min, so both final points must be plotted accurately. Join the points with one smooth curve rather than separate straight-line sections.

Common mistakes

• Putting time on the vertical axis or corrected count rate on the horizontal axis.
• Leaving out the units, or using an uneven scale.
• Missing the close final points, especially (4.0, 5) and (4.5, 6).
• Joining points with a series of straight segments or drawing several separate curves instead of one smooth curve.

Example 2: Using a Diagram

Question 2

Scientists use the term radiation in different ways.
Sometimes radiation means streams of particles and sometimes radiation means high frequency waves.

People who work with ionising radiations need to measure the amount of radiation they are exposed to.
For many years, a film badge was used to detect the radiations.
The diagram shows how a film badge is constructed.
Each absorber window is made from different thicknesses of paper, aluminium or lead.
Complete the table to show if alpha, beta and gamma radiations penetrate each material. Some have been done for you.
Use the words ‘goes through’ or ‘stopped’.

	0.1 cm paper	0.5 cm aluminium	0.5 cm lead
alpha radiation	stopped
beta radiation		stopped
gamma radiation	goes through

Final answer

	0.1 cm paper	0.5 cm aluminium	0.5 cm lead
alpha radiation	stopped	stopped	stopped
beta radiation	goes through	stopped	stopped
gamma radiation	goes through	goes through	goes through

Mark scheme points

1. M1 The complete alpha radiation row is correct.
2. M2 The complete beta radiation row is correct.
3. M3 The complete gamma radiation row is correct.

Explanation

Alpha radiation has the least penetrating power, so it is stopped by all three absorbers.

Beta radiation passes through the thin paper but is stopped by the thicker aluminium and lead.

Gamma radiation is the most penetrating, so it goes through all three materials shown.

Common mistakes

• Do not write that alpha radiation goes through paper; it is stopped.
• Do not stop beta radiation with the paper column; beta goes through the paper.
• Gamma radiation goes through every material and thickness listed in this table.
• Use exactly “goes through” or “stopped” rather than vague descriptions such as “partly blocked”.

Practise Radioactivity questions

Build a focused practice set from this part of the Edexcel IGCSE Physics syllabus.