AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), November 2021: Question 6
10 marks · Standard Demand difficulty · Extended Answer
Demonstrate the properties and detection of alpha, beta, and gamma radiation, including the relative size of an atom compared to its nucleus and the mechanism of ionisation.
Practise this questionQuestion
Question text
06 A radioactive source emits alpha, beta and gamma radiation.
06.1 An alpha particle is the same as a helium nucleus.
How many times bigger is the radius of a helium atom than the radius of an
alpha particle?
[1 mark]
Tick ( ) one box.
Less than 100 times bigger
Exactly 5000 times bigger
More than 10 000 times bigger
06.2 Alpha particles can ionise atoms in the air.
What happens to an atom when it is ionised by an alpha particle?
[2 marks]
Tick ( ) two boxes.
A neutron in the atom becomes a proton.
The atom becomes a positive ion.
The atom gains a neutron.
The atom gains a proton.
The atom loses an electron. 28
06.3 A spark detector is a device that can be used to detect alpha radiation.
A spark detector works by alpha particles ionising atoms in the air near a wire mesh.
A large potential difference creates a spark when the air near the wire mesh
is ionised.
Suggest why a spark detector cannot detect beta radiation.
[1 mark]
06.4 A teacher wants to demonstrate that the radioactive source emits alpha, beta and
gamma radiation.
Figure 11 shows the equipment the teacher has.
Figure 11
Describe a method the teacher could use.
[6 marks]
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
06.1 more than 10 000 times bigger 1 AO1
6.4.1.1
06.2 the atom becomes a positive ion 1 AO1
6.4.1.2
the atom loses an electron 1
06.3 beta radiation is only weakly 1 AO3
ionising – OMBINED SCIENCE: TRILOGY – – J6.4.2.1UNE 2021
AO /
Question Answers Mark
Spec. Ref.
Level 3: The method would lead to the production of a valid 5–6 AO3
06.4
outcome. The key steps are identified and logically sequenced. 6.4.2.1
Level 2: The method would not necessarily lead to a valid 3–4
outcome. Most steps are identified, but the method is not fully
logically sequenced.
Level 1: The method would not lead to a valid outcome. Some 1–2
relevant steps are identified, but links are not made clear.
No relevant content 0
Indicative content
• move the detector very close to the source
• record the count rate
• position the paper between the source and the detector
• record the new count rate
• alpha radiation will not penetrate through paper
• if the count rate with the paper is (significantly) less than without
then the source emits alpha radiation
• remove the paper and position the aluminium between the
source and the detector
• record the new count rate
• (alpha and) beta radiation will not penetrate through the
aluminium
• if the count rate has (significantly) reduced compared with using
16 paper then beta radiation is present
• if radiation penetrates through the aluminium then gamma
radiation is present
• the experiment should be repeated and mean results calculated
because radioactivity is a random process
To access level 3, the candidate must use the paper sheet, the
aluminium sheet and no sheet, and describe how the results would
indicate the presence of alpha, beta or gamma radiation.
Total 10
How to answer it
Atomic Structure and Nuclear Radiation
This question assesses key knowledge of atomic scale, the physical process of ionisation, relative ionising power of alpha and beta radiation, and the classic penetration experiment using absorbing materials (paper and aluminium) to identify alpha, beta, and gamma emissions.
Size Comparison: Atom vs Nucleus
Scale of an atom compared to an alpha particle (helium nucleus)
✅ Correct Answer
- [✓] More than 10 000 times bigger
💡 Key Knowledge
- An alpha particle is simply a helium nucleus (2 protons + 2 neutrons).
- Radius of an atom: approximately 1 × 10⁻¹⁰ m.
- Radius of a nucleus: less than 1 × 10⁻¹⁴ m (around 10 000 to 100 000 times smaller).
❌ Common Errors
Choosing "Exactly 5000 times bigger" or "Less than 100 times bigger". Students often forget just how empty an atom is: the vast majority of atomic volume is empty space around the tiny nucleus.
Mechanism of Ionisation
What happens to a neutral atom when ionised by alpha particles?
✅ Correct Answers (Tick 2 boxes)
- [✓] The atom becomes a positive ion. (1 mark)
- [✓] The atom loses an electron. (1 mark)
💡 Key Knowledge
- Ionisation is the process where radiation knocks orbiting electrons free from neutral atoms.
- Loss of a negatively charged electron leaves behind more protons than electrons, giving the atom an overall positive charge.
🧠 Exam Technique
Always link the two selected answers logically: removing a negative electron directly explains why the remaining particle must become a positive ion.
❌ Common Errors
- Selecting "A neutron in the atom becomes a proton" (confusing atomic ionisation with beta-minus radioactive decay).
- Thinking ionisation changes the nucleus by gaining or losing protons.
Why a Spark Detector Cannot Detect Beta Radiation
Relating ionising ability to practical device function
✅ Correct Answer
Beta radiation is only weakly ionising (or not ionising enough / less ionising than alpha).
💡 Key Knowledge: Ionising Power
- Alpha: Strongly ionising (large charge +2, high mass). Creates enough charged ions in air to trigger a visible spark across the high-voltage gap.
- Beta: Moderately / weakly ionising.
- Gamma: Very weakly ionising.
❌ Common Errors
Writing about penetration instead of ionisation (e.g., saying "beta passes straight through the mesh" or "beta has too much range"). The stem explicitly states that the detector works by ionising air, so the reason it fails for beta must relate directly to ionisation power.
6-Mark Practical: Identifying Radiation Types
Describe an experiment using paper and aluminium to prove the source emits alpha, beta, and gamma
🧠 How to Get Level 3 (5–6 Marks)
To access Level 3, the method must describe measurements with: (1) no absorber, (2) paper, and (3) aluminium sheet, AND explicitly state how each result confirms the presence of alpha, beta, and gamma radiation.
📐 Step-by-Step Practical Method
- Set-up & Baseline Count:
Place the radiation detector close to the source (within 2–3 cm, so short-range alpha can reach it). Measure and record the count rate with no absorber. - Test for Alpha Radiation (Paper):
Place a thin sheet of paper between the source and detector. Record the new count rate.
Deduction: Alpha cannot penetrate paper. If the count rate drops significantly, alpha radiation is present. - Test for Beta Radiation (Aluminium):
Remove the paper and place the 3 mm aluminium sheet between source and detector. Record the count rate.
Deduction: Beta cannot penetrate aluminium (alpha is also stopped). If the count rate decreases significantly compared to using paper alone, beta radiation is present. - Test for Gamma Radiation:
Observe the count rate through the 3 mm aluminium sheet.
Deduction: Gamma radiation penetrates aluminium. If the count rate is still higher than background radiation, gamma radiation is present. - Experimental Reliability:
Repeat the measurements and calculate mean count rates (radioactive decay is a random process).
✅ Summary of Deductions
- Count rate drops with paper: Alpha confirmed.
- Count rate drops further with aluminium: Beta confirmed.
- Radiation still passes through aluminium: Gamma confirmed.
❌ Common Errors in 6-Markers
- Placing detector too far away: Alpha only travels ~3–5 cm in air; if the detector is 20 cm away, alpha will not be detected even with no barrier.
- Stating what stops radiation without describing measurements: Just writing "paper stops alpha, aluminium stops beta" gives no method and caps marks at Level 1.
- Omitting the baseline: Forgetting to measure the count rate with no sheet first.
Topics
Physics · P4: Atomic Structure
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.