AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2022: Question 6

11 marks · Standard Demand difficulty · Extended Answer

Explain hazards and identify properties of alpha and beta radiation, complete an alpha decay equation, use barrier data to determine emitted nuclear radiation, and use an activity-time graph to rank isotopes by nuclear stability.

Practise this question

Question

The question page shows Question 06 with four parts about nuclear radiation. Part 06.1 states that a smoke detector contains a source of alpha radiation in a plastic case and asks why a beta source would be more hazardous than an alpha source for 2 marks. Part 06.2 says actinium emits an alpha particle and turns into francium, showing the nuclear equation with unknown mass number A and atomic number Z for actinium on the left and 223 over 87 next to Fr plus an alpha particle on the right, then asks for A and Z for 2 marks. Part 06.3 describes an investigation using barriers between a source and detector, with a table of counts after 30 seconds: none gives 985, paper 0.1 mm gives 149, aluminium 5.0 mm gives 0, and lead 20.0 mm gives 0; it asks what nuclear radiation was emitted for 4 marks. Part 06.4 shows a graph titled Figure 11 of activity in becquerels against time in years for isotopes A, B, C and D, with four decreasing curves starting at different activities and ending at different values by about 20 years, and asks for the order of increasing stability with an explanation for 3 marks.
Question text

06 A smoke detector contains a source of alpha radiation in a plastic case.

06.1 A source of beta radiation in a smoke detector would be more hazardous than a

source of alpha radiation.

Explain why.

[2 marks]

06.2 Actinium (Ac) is one source of alpha radiation.

An actinium (Ac) nucleus emits an alpha particle (α) and turns into a

francium (Fr) nucleus.

This can be represented as:

Determine the values of A and Z.

[2 marks]

A =

25 Z =

06.3 A teacher wanted to find out what nuclear radiation is emitted from a source.

The teacher placed different barriers between the source and a detector.

The teacher recorded the count for 30 seconds after each barrier was put in place.

Table 2 shows the results.

Table 2

Barrier Thickness in Count after 30

millimetres seconds

None 985

Paper 0.1 149

Aluminium 5.0 0

Lead 20.0 0

Explain what nuclear radiation was emitted by the source.

[4 marks]

06.4 Figure 11 shows how the activity of four different radioactive isotopes, A, B, C and D,

changes over time.

Figure 11

Write the isotopes A, B, C and D in order of increasing stability of their nuclei.

Explain your answer.

[3 marks]

Least stable Most stable

Explanation

Mark scheme

Show the mark scheme The mark scheme is presented in four table sections for Questions 06.1 to 06.4 with columns for answers, extra information, marks and specification references. For 06.1 it credits that beta radiation is more penetrating than alpha and therefore could irradiate people because it can pass through the case or skin; for 06.2 it gives A = 227 and Z = 89. For 06.3 it credits identifying alpha because some radiation is stopped by paper and beta because some passes through paper but is stopped by aluminium, concluding no gamma is emitted. For 06.4 it gives the stability order D B A C and explains that longer half-life means a more stable nucleus, so the order follows increasing half-life; the total for Question 6 is 11 marks.

Question 6

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 beta radiation is more allow beta radiation can pass 1 AO1

penetrating (than alpha through the case (but alpha 6.4.2.1

radiation) radiation cannot) 6.4.2.4

allow beta radiation can travel

further (in air than alpha

radiation)

do not allow beta radiation is

more ionising

so beta radiation could irradiate allow beta radiation can pass 1

people passing near the smoke through skin

detector

AO /

Spec. Ref.

06.2 A = 227 1 AO1

Z = 89 1 AO2

6.4.2.2

6.4.2.1

6.4.1.2

AO /

Spec. Ref.

06.3 (some) radiation is stopped by 1 AO3

paper 6.4.2.1

so the source emits alpha MP2 dependent on MP1 1

radiation

and (some) radiation passes 1

through paper but is stopped by 19

aluminium

so the source emits beta MP4 dependent on MP3 1

radiation (but does not emit

gamma)

AO /

Spec. Ref.

06.4 D B A C all four letters must be in the 1 AO3

correct order 6.4.2.1

6.4.2.3

explanation only scores if

correct order given

explanation

a substance with a longer half- allow the more stable a nucleus, 1

life has more stable nuclei the less likely it is to decay (in a

given time)

so answers are in order of 1

increasing half-life

Total Question 6 11

How to answer it

Radioactivity in a Smoke Detector

What this question tests

You need to know the properties of alpha, beta and gamma radiation, how nuclear equations change in alpha decay, how to identify a source from barrier test results, and how half-life/activity relates to nuclear stability.

Overall mark focus: 11 marks

Part (a) 06.1 — Why beta is more hazardous than alpha in a smoke detector

✅ Correct answer

Beta radiation is more penetrating than alpha radiation, so it could pass through the plastic case and irradiate people nearby.

💡 Key knowledge

  • Alpha is stopped by paper or skin.
  • Beta can travel further and can pass through paper and sometimes skin.
  • Hazard here means people could be exposed, not just that the radiation exists.

🧠 Exam technique

  • To get 2 marks, give property + consequence.
  • Good structure: beta is more penetrating → can pass through the case → can irradiate people .

❌ Common errors

  • Saying beta is “more ionising” — that is not the reason.
  • Only saying “beta goes further” without linking it to the smoke detector case.
  • Mixing up alpha and beta penetration.
How marks were awarded: 1 mark for saying beta is more penetrating / can pass through the case, and 1 mark for explaining that this could expose or irradiate people nearby.

Part (b) 06.2 — Determining A and Z in alpha decay

Ac decay: A Ac → ²²³₈₇Fr + α

✅ Correct answers

A = 227
Z = 89

💡 Key knowledge

  • An alpha particle is ⁴₂He.
  • In alpha decay:
    • mass number decreases by 4
    • atomic number decreases by 2

📐 Calculation / method

  1. Balance the mass numbers: 223 + 4 = 227
  2. Balance the atomic numbers: 87 + 2 = 89

🧠 Exam technique

  • Always check both sides of the equation.
  • Remember: alpha emission makes the nucleus lighter and less charged.

❌ Common errors

  • Forgetting that alpha is ⁴₂He, not just “α” when balancing numbers.
  • Getting the atomic number change the wrong way round.
  • Writing A = 223 and Z = 87 from the fransium side instead of the actinium parent nucleus.

✅ Full-mark answer format

A = 227
Z = 89

Part (c) 06.3 — Identifying the radiation from barrier results

✅ Correct answer

The source emits alpha and beta radiation, but not gamma.

💡 Key knowledge

  • Alpha: stopped by paper.
  • Beta: passes through paper but is stopped by aluminium.
  • Gamma: would need thick lead/concrete to reduce strongly, and would not be stopped by paper or aluminium in this simple test.

🧠 Exam technique

  • Use the pattern of counts to eliminate each type.
  • Full marks come from linking each barrier result to a radiation type.
  • Write in a logical order: paper → aluminium → conclusion.

❌ Common errors

  • Saying only one radiation type when the evidence shows two.
  • Ignoring the fact that some radiation still passes through paper.
  • Claiming gamma because lead was used, even though the counts were already zero with aluminium.

📐 Step-by-step reasoning

  1. With no barrier, the count is high: 985.
  2. With paper, the count drops a lot to 149, so some radiation is stopped by paper → this is alpha.
  3. But not all radiation is stopped by paper, because some still gets through.
  4. With aluminium, the count becomes 0, so the radiation that passed through paper is now stopped → this is beta.
  5. Because aluminium stops it, and lead also gives 0, there is no evidence for gamma.
How marks were awarded: marks were available for identifying alpha from paper, beta from paper + aluminium, and the final conclusion that gamma was not emitted.

Part (d) 06.4 — Ordering isotopes by nuclear stability

✅ Correct order

D, B, A, C

Least stable → most stable

💡 Key knowledge

  • More stable nucleus = longer half-life.
  • More stable nuclei decay more slowly, so their activity falls more slowly.
  • On a decay graph, the isotope with the steepest drop is the least stable.

🧠 Exam technique

  • Use the graph to compare how quickly activity decreases.
  • If two curves are close, compare the overall change over the same time.
  • The question asks for increasing stability, so go from fastest decay to slowest decay.

❌ Common errors

  • Writing the letters in the wrong order.
  • Confusing activity with stability.
  • Thinking the highest starting activity means the most stable nucleus. It does not.

📐 How to read the graph

  1. D falls the fastest, so it has the shortest half-life and is the least stable.
  2. B falls more quickly than A and C, but less quickly than D.
  3. A falls more slowly than B, so it is more stable.
  4. C changes the least, so it is the most stable.

✅ Full-mark explanation

A substance with a longer half-life has more stable nuclei, because the nuclei are less likely to decay in a given time. Therefore the order is based on increasing half-life: D, B, A, C.

How marks were awarded: 1 mark for the correct order, and marks for stating that longer half-life means greater stability / slower decay.

Quick revision summary

Alpha radiation

  • Stopped by paper
  • Very ionising
  • Low penetration

Beta radiation

  • More penetrating than alpha
  • Stopped by aluminium
  • Can pass through skin

Gamma radiation

  • Most penetrating
  • Needs thick lead or concrete to reduce
  • Not stopped by paper or thin aluminium

Topics

Physics · P4: Atomic Structure

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Higher), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.