Practise 36 exam-style questions on Radioactive decay and nuclear radiation for AQA GCSE Physics. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
36 questions
1–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
State what is meant by the activity of a radioactive source.
Give the unit of activity.
Model answer
Activity is the rate at which the unstable nuclei in a source decay, that is the number of decays each second. It is measured in becquerels (Bq).
Explanation
Activity describes the source itself: how many of its nuclei decay every second. One becquerel is one decay per second. Do not confuse activity with count-rate, which is only the number of decays a detector actually records each second.
Mark scheme
1 mark
the rate at which the unstable nuclei in the source decay
allow the number of nuclei that decay each second / the number of decays per second; do not accept the number of counts recorded per second (that is count-rate)
1 mark
becquerel / Bq
allow decays per second
Question 2
2 marks
A student measures the count-rate from a radioactive source. She records the number of counts over 5 minutes, rather than over 10 seconds.
Explain why counting for a longer time gives a more accurate value for the count-rate.
Model answer
Radioactive decay is random, so the number of counts in a short time varies a lot from one reading to the next. Counting for 5 minutes gives many more counts, so the random fluctuations have much less effect on the average count-rate.
Explanation
In 10 seconds a source might give 8 counts one time and 14 the next, purely by chance. Over a long time these random ups and downs average out, so the count-rate calculated is much closer to the true value.
Mark scheme
1 mark
radioactive decay is random so the number of counts in a short time varies / fluctuates
1 mark
a longer time gives many more counts so the random variations have a smaller effect
allow gives a more representative average count-rate
Question 3
3 marks
A radioactive source has an activity of 3.6 kBq. A Geiger-Müller tube is placed 25 cm from the source. After correcting for background radiation, the count-rate is 1.2 counts per second.
Calculate the percentage of the decays in the source that are recorded by the detector.
Model answer
Activity = 3.6 kBq = 3600 decays per second Percentage recorded = (1.2 ÷ 3600) × 100 = 0.033 %
Explanation
Activity is the total number of decays per second in the source, while count-rate is only what the detector records. Here only about 1 decay in 3000 is recorded, because the radiation spreads out in all directions and some is absorbed before it reaches the tube.
Mark scheme
1 mark
3.6 kBq = 3600 Bq / decays per second
an answer of 0.033 (%) scores 3 marks
1 mark
(1.2 ÷ 3600) × 100
1 mark
0.033 (%)
allow 0.0333... / 0.03; allow ecf from an incorrect conversion (e.g. 33 % scores 2 marks)
Question 4
4 marks
Describe what happens to the numbers of protons and neutrons in a nucleus when it emits each of the following: an alpha particle a beta particle a gamma ray
Model answer
When a nucleus emits an alpha particle it loses two protons and two neutrons. When it emits a beta particle, a neutron turns into a proton, so there is one neutron fewer and one proton more. When it emits a gamma ray, the numbers of protons and neutrons stay the same; the nucleus just loses energy.
Explanation
An alpha particle carries away two protons and two neutrons. In beta decay the total number of particles in the nucleus is unchanged, but one neutron becomes a proton. A gamma ray is only energy, so the nucleus keeps all its particles.
Mark scheme
1 mark
alpha: the nucleus loses two protons and two neutrons
both needed
1 mark
beta: a neutron turns into a proton
1 mark
so the number of neutrons decreases by one and the number of protons increases by one
1 mark
gamma: the numbers of protons and neutrons do not change
allow the nucleus just loses energy
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