AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), 2023: Question 1

11 marks · Low Demand difficulty · Short Answer

Identify properties of alpha and gamma radiation, balance a nuclear decay equation, calculate count-rate and half-life activity, and explain radiation safety and irradiation.

Practise this question

Question

A multi-part physics exam question about radioactive isotopes. It includes a nuclear equation for the alpha decay of polonium-210 to lead, a diagram of experimental equipment (source, detector, counter, stopwatch), and a photograph of a person using long tongs to hold a radioactive source. Questions cover identifying alpha radiation, proton numbers, balancing nuclear equations, calculating half-life activity, determining count-rates, and safety precautions like irradiation and shielding.
Question text

01 A scientist investigated the radiation emitted by different radioactive isotopes.

The scientist had a sample of polonium-210.

The radiation emitted by polonium-210 can be represented by the symbol 4 He.

01.1 Which type of radiation can be represented by the symbol 4 He?

[1 mark]

Tick ( ) one box.

Alpha

Beta

Gamma

01.2 How many protons are there in a particle of radiation represented by 4 He?

[1 mark]

Tick ( ) one box.

24 6 8

01.3 A polonium-210 (Po) nucleus changes into a lead (Pb) nucleus by emitting a

4 He particle. This is shown by the following nuclear equation.

210Po → 206Pb + 4He

84 X 2

What is the value of X?

[1 mark]

Tick ( ) one box.

80 82 843 86

01.4 The sample of polonium-210 had an activity of 100 Bq.

Complete the sentence.

Choose the answer from the box.

*02* [1 mark]

25 50 100 200

After one half-life, the activity of polonium-210 in the sample

was Bq.

The scientist investigated another radioactive isotope that is a source of gamma

radiation.

Figure 1 shows the equipment used.

Figure 1

01.5 The count-rate is the number of counts detected each second.

In 30 seconds the number of counts detected was 1500.

Calculate the count-rate.

[2 marks]

Count-rate = counts per second

The scientist placed a thick sheet of lead between the source of gamma radiation and

the detector.

01.6 What was the effect of the sheet of lead on the count-rate?

*03* Give a reason for your answer.

[2 marks]

Effect

Reason

01.7 The lead was irradiated by the gamma radiation.

*04* What happened to the lead when it was irradiated by the gamma radiation?

[1 mark]

Tick ( ) one box.

The lead atoms became radioactive.

The lead gained atoms from the radioactive source.

The lead was exposed to gamma radiation.6

01.8 Gamma radiation is emitted from the nucleus of an atom.

Complete the sentence.

Choose the answer from the box.

[1 mark]

electromagnetic waves high speed electrons

neutrons positively charged ions

Gamma radiation consists of .

01.9 Figure 2 shows the scientist holding the radioactive source using tongs.

Figure 2

Suggest one reason why using long tongs rather than short tongs was safer for

the scientist.

[1 mark]

Mark scheme

Show the mark scheme The mark scheme provides answers for questions 01.1 to 01.9, totaling 11 marks. Key answers include 'alpha' for radiation type, '2' for proton number, '82' for the missing atomic number in the equation, and '50' for activity after one half-life. It also details the calculation for count-rate (1500/30 = 50), explains that lead decreases count-rate because it absorbs gamma radiation, defines irradiation as exposure, identifies gamma as electromagnetic waves, and lists safety benefits of using long tongs to increase distance.

Question 1

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 alpha 1 AO1

6.4.2.2

AO /

Spec. Ref.

01.2 2 1 AO1

6.4.2.1

AO /

Spec. Ref.

01.3 82 1 AO2

6.4.2.2

AO /

Spec. Ref.

01.4 50 1 AO1

6.4.2.3

AO /

Spec. Ref.

01.5 1500 1 AO2

30 6.4.2.1

50 (counts per second) 1

AO /

Spec. Ref.

01.6 the count-rate decreased allow decreased to (almost) zero 1 AO1

6.4.2.1

because (gamma) radiation is allow (gamma) radiation cannot 1

absorbed by lead – OMBINED SCIENCE: TRIpenetrate (thick) leadLOGY – 1F –

AO /

Spec. Ref.7

01.7 the lead was exposed to gamma 1 AO1

radiation 6.4.2.4

AO /

Spec. Ref.

01.8 electromagnetic waves 1 AO1

6.4.2.1

AO /

Spec. Ref.

any one from: 1

01.9 AO1

• (longer tongs give) a greater 6.4.2.4

distance between the scientist

and the radioactive source

• (longer tongs) reduce the

amount of radiation the

scientist is exposed to

• (longer tongs) reduce the risk allow (longer tongs) reduce the

of cell mutation risk of cancer

Total Question 1 11

How to answer it

Radioactive Decay and Radiation Properties

What this question tests:

This question assesses your ability to identify types of nuclear radiation (Alpha and Gamma), balance nuclear equations, calculate half-life and count-rates, and understand the difference between irradiation and contamination alongside safety procedures.

Part 01.1 & 01.2: Identifying Alpha Particles

💡 Key Knowledge

  • The symbol ⁴₂He represents an Alpha particle.
  • An alpha particle is identical to a Helium nucleus.
  • The top number (4) is the mass number (protons + neutrons).
  • The bottom number (2) is the atomic number (protons).

✅ Correct Answers

01.1: Alpha

01.2: 2 (protons)

1 Mark each

Part 01.3: Nuclear Equations

The Equation: ²¹⁰₈₄Po → ²⁰⁶ₓPb + ⁴₂He

🧠 Exam Technique

In nuclear equations, the total mass and atomic numbers must be the same on both sides of the arrow.

To find X, look at the bottom numbers:

84 = X + 2

Therefore, X = 82 .

✅ Correct Answer

82

1 Mark

Part 01.4 & 01.5: Activity and Count-Rate

📐 Calculations

01.4 Half-life: After one half-life, the activity halves.

  1. Start activity = 100 Bq
  2. 100 ÷ 2 = 50 Bq

01.5 Count-rate: This is counts per second.

  1. Total counts = 1500
  2. Time = 30 seconds
  3. 1500 ÷ 30 = 50 counts per second

❌ Common Errors

  • Units: Ensure you don't confuse Bq (Becquerels) with counts per second, though they represent the same rate here.
  • Time: Always check if time is in seconds. If it was in minutes, you would need to multiply by 60 first!

Part 01.6 & 01.7: Gamma Radiation & Irradiation

💡 Key Knowledge

  • Penetration: Gamma is the most penetrating radiation. It passes through paper and aluminium but is absorbed by thick lead or concrete.
  • Irradiation: This means being exposed to radiation. It does not make the object radioactive.

🧠 Examiner Commentary

Students often confuse irradiation with contamination. Contamination involves radioactive atoms actually getting onto or into an object. Irradiation is just like standing in light—once you move away, the exposure stops.

✅ Correct Answers

01.6 Effect: The count-rate decreased (or went to zero).

01.6 Reason: Gamma radiation is absorbed by lead (or cannot penetrate thick lead).

01.7: The lead was exposed to gamma radiation.

3 Marks total

Part 01.8 & 01.9: Nature of Gamma & Safety

💡 Key Knowledge

Gamma radiation is part of the electromagnetic spectrum. Unlike Alpha or Beta, it is a wave, not a particle, so it has no mass and no charge.

🧠 Safety: Using Tongs

The further you are from a source, the lower the intensity of radiation reaching you. Long tongs increase the distance between the scientist and the source.

✅ Correct Answers

01.8: electromagnetic waves

01.9: (Any one) Increases distance / reduces exposure / reduces risk of cancer or cell mutation.

2 Marks total

Topics

Physics · P4: Atomic Structure

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.