Lesson 6.4.2.3

6.4.2.3 Half-lives and the random nature of radioactive decay Quiz: AQA Combined Science, Unit 21

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6.4.2.3, Half-lives and the random nature of radioactive decay: 20 multiple choice questions for the AQA GCSE Combined Science (8464), Unit 21: Atomic structure, written with Revision Ninja.

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The 20 questions

  1. What is defined as the time taken for the number of nuclei in a sample to halve?

    • Count-rate
    • Decay constant
    • Half-life
    • Activity rate

  2. What does half-life predict for large radioactive samples?

    • Zero final activity
    • Exact decay time
    • A predictable average
    • Individual nucleus life

  3. What alternative measurement decreases by half during one half-life period?

    • Count-rate
    • Neutron number
    • Total mass
    • Atomic number

  4. Which property of radioactive decay explains why half-life must be defined statistically?

    • Fixed energy
    • Deterministic decay
    • Constant rate
    • Random nature

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

    • It increases with mass
    • It decreases over time
    • It is constant
    • It varies randomly

  6. After one half-life, what fraction of the original nuclei remains?

    • Three quarters
    • One quarter
    • One tenth
    • One half

  7. After two half-lives, what fraction of the original nuclei remains?

    • Zero
    • One quarter
    • One eighth
    • One half

  8. A sample has a half-life of 5 minutes. How long does its count rate take to halve twice?

    • 20 minutes
    • 5 minutes
    • 10 minutes
    • 2.5 minutes

  9. What fraction of radioactive nuclei remain in a sample after exactly one half-life?

    • Zero
    • One quarter
    • One half
    • Three quarters

  10. A count rate starts at 800 counts per minute. What is it after one half-life?

    • 400 counts per minute
    • 600 counts per minute
    • 200 counts per minute
    • 1600 counts per minute

  11. A count rate falls from 320 counts per second to 40 counts per second. How many half-lives have passed?

    • 5
    • 3
    • 4
    • 2

  12. An activity of 1200 Bq halves to 300 Bq in 6 hours. What is the half-life?

    • 2 hours
    • 3 hours
    • 1.5 hours
    • 6 hours

  13. A sample has a half-life of 2 days. What fraction remains after 6 days?

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

  14. A graph shows count rate falling from 600 to 300 between 0 s and 40 s. What is the half-life?

    • 80 s
    • 40 s
    • 600 s
    • 20 s

  15. A sample has a count of 800 at the start. What is the count after 3 half-lives?

    • 100
    • 50
    • 400
    • 200

  16. A sample's count falls from 1000 to 125 in 9 hours. What is its half-life?

    • 1.5 hours
    • 4.5 hours
    • 3 hours
    • 9 hours

  17. (Higher tier) A count rate is 4800 and then falls to 300. How many half-lives have passed?

    • 4
    • 5
    • 3
    • 6

  18. (Higher tier) What is the ratio of the initial emission to the emission after 4 half-lives?

    • 8 : 1
    • 16 : 1
    • 2 : 1
    • 4 : 1

  19. A source has half-life 10 minutes. Its count rate falls from 500 to 62.5. How long has passed?

    • 20 minutes
    • 30 minutes
    • 60 minutes
    • 40 minutes

  20. A 2 g sample has a half-life of 1 year. What mass remains after 3 years?

    • 0.25 g
    • 1 g
    • 0.125 g
    • 0.5 g

All AQA Combined Science quizzes