Lesson 4.4.2.3

4.4.2.3 Half-lives and the random nature of radioactive decay Quiz: AQA Physics, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.4.2.3, Half-lives and the random nature of radioactive decay: 20 multiple choice questions for the AQA GCSE Physics (8463), Unit 4: Atomic structure, written with Revision Ninja.

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The 20 questions

  1. What halves during the half-life of a radioactive isotope?

    • Proton count
    • Atomic radius
    • Nuclei number
    • Total mass

  2. What term describes the time taken for a radioactive count rate to halve?

    • Half-life
    • Activity time
    • Decay constant
    • Period

  3. Why is radioactive decay described as random?

    • Always constant
    • Occurs linearly
    • Happens simultaneously
    • Impossible to predict

  4. What is true about the half-life of a specific radioactive isotope?

    • It varies randomly
    • It decreases
    • It increases
    • It is constant

  5. A sample has an activity of 80 Bq. What is its activity after one half-life?

    • 80 Bq
    • 20 Bq
    • 160 Bq
    • 40 Bq

  6. A sample starts with an activity of 800 Bq. What is its activity after two half-lives?

    • 400 Bq
    • 100 Bq
    • 0 Bq
    • 200 Bq

  7. The count rate from a sample falls from 640 counts per minute to 320 counts per minute in 6 hours. What is the half-life?

    • 12 hours
    • 3 hours
    • 6 hours
    • 320 hours

  8. A source has a half-life of 4 days. How long does it take for its activity to fall to one quarter?

    • 4 days
    • 16 days
    • 8 days
    • 2 days

  9. A source has a half-life of 10 minutes and a count rate of 1200 counts per minute at the start. What is the count rate after 30 minutes?

    • 300 counts per minute
    • 150 counts per minute
    • 0 counts per minute
    • 200 counts per minute

  10. (HT only) Activity halves three times. What is the ratio of final activity to initial activity?

    • 1 : 8
    • 1 : 3
    • 1 : 6
    • 3 : 1

  11. (HT only) A source has an initial activity of 400 Bq. What is its activity after four half-lives?

    • 25 Bq
    • 100 Bq
    • 0 Bq
    • 50 Bq

  12. (HT only) What is the net decline, expressed as a ratio of initial to final emission, after five half-lives?

    • 16 : 1
    • 10 : 1
    • 32 : 1
    • 5 : 1

  13. A sample has an activity of 500 Bq at the start, 250 Bq after 12 days and 125 Bq after 24 days. What is its half-life?

    • 6 days
    • 12 days
    • 24 days
    • 250 days

  14. Why do measured count rates sometimes deviate slightly from expected halving times?

    • Systematic error
    • Temperature effects
    • Pressure changes
    • Decay is random

  15. A radioisotope has a half-life of 2 hours. How long does it take for the activity to fall to one eighth of its starting value?

    • 8 hours
    • 6 hours
    • 4 hours
    • 2 hours

  16. What defines the half-life of a radioactive isotope?

    • Mass halves
    • Activity doubles
    • Activity halves
    • All nuclei decay

  17. A source has a half-life of 5 minutes and an initial count rate of 4800 counts per minute. What is the count rate after 15 minutes?

    • 300 counts per minute
    • 800 counts per minute
    • 1200 counts per minute
    • 600 counts per minute

  18. What does half-life actually describe in relation to individual atoms?

    • Simultaneous decay
    • Average behaviour
    • Exact lifespan
    • Forced reaction

  19. A count rate is 3200 counts per minute at time zero and 1600 counts per minute at 10 minutes. What is the half-life?

    • 5 minutes
    • 1600 minutes
    • 10 minutes
    • 20 minutes

  20. A sample has a half-life of 30 days. What fraction of the original nuclei remain after 90 days?

    • One half
    • One eighth
    • One sixth
    • One quarter

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