A LevelPhysicsAQAExam QuestionsNuclear PhysicsRadioactive Decay

Radioactive Decay (AQA A Level Physics)

Exam Questions

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Radioactive Decay

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Radioactive Decay

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11 mark

Which of the following statements about the random process of radioactive decay is incorrect?

  • An estimate of the proportion of nuclei decaying in a given time period can be known

  • There is an equal probability of any nucleus decaying 

  • It cannot be known which particular nucleus will decay next

  • It can be known at what time a particular nucleus will decay

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21 mark

Which of the following is the unit for the decay constant λ?

  • Bq s–1

  • s

  • s–1

  • No units

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31 mark

Which of the following graphs of the number of undecayed nuclei N over time has the smallest decay constant?

q3-8-2-mcq-radioactive-decay

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    41 mark

    What is the half–life from the graph in the diagram below?

    q4-8-2-mcq-radioactive-decay

    • 9 s

    • 25 s

    • 40 s

    • 5 s

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    51 mark

    What is the decay constant for plutonium–238 which has a half–life of 88 years?

    • 61 year–1

    • 127 year–1

    • 7.9 × 10–3 year–1

    • 1.1 × 10–2 year–1

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    11 mark

    After 75 days the activity of a radioactive nuclide is reduced by a factor of 1 over 32.

    What is the half–life of the radioactive nuclide?

    • 3 days

    • 15 days

    • 10 days

    • 7.5 days  

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    21 mark

    The activity of a sample of polonium–214 reduces to a third of its initial value in 260 µs. 

    What is the half-life of polonium–214?

    • 100 µs

    • 87 µs

    • 164 µs

    • 135 µs

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    31 mark

    A pure sample of nuclide P containing N nuclei has an activity A. The half–life of P is 4000 years. A pure sample of nuclide Q containing 4N nuclei has an activity 6A.

    What is the half–life of nuclide Q?

    • 1500 years

    • 6000 years

    • 2700 years

    • 13 000 years

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    41 mark

    The graph below shows the amount of radiation emitted by a sample of U–238 as time passes.

    q9-8-2-mcq-radioactive-decay

    What fraction of the U–238 nuclei will have decayed after 9 billion years?

    • 1 half

    • 1 fourth

    • 1 third

    • 3 over 4

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    51 mark

    A radioactive source has a half–life of 12 minutes. A detector connected to a Geiger–counter records a rate of 45 counts s–1.

    Which rate is recorded after 60 minutes?

    • 12 counts s–1

    • 1.4 counts s–1

    • 2.8 counts s–1

    • 5.0 counts s–1

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    11 mark

    Radium–226 has a half–life of 1600 years.

    What is the total activity of 3.0 g of radium–226?

    • 3.5 × 1018Bq

    • 1.1 × 1011Bq

    • 6.2 × 1014Bq

    • 2.8 × 1012Bq

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    21 mark

    A radioactive source X consists of 7.3 × 1011 atoms of a nuclide of half–life 5 days. A second source Y consists of 5.2 × 1010 atoms of another nuclide of half–life 6 days.

    After how many days will the number of radioactive atoms in X be equal to Y?

    • 162 days

    • 120 days

    • 114 days

    • 7.9 days

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    31 mark

    The graph below shows the relationship between the number of particles, N, emitted by a radioactive source and the time. The source consists of a single isotope that does not produce any radioactive daughter nuclei when it decays.

    q13-8-2-mcq-radioactive-decay

    What is the half–life of the isotope?

    • 20.1 s

    • 32.5 s

    • 0.13 s

    • 7.51 s

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    41 mark

    Two radioactive elements X and Y have half–lives T subscript X and T subscript Y respectively. Initially samples of S, N subscript X contains three times as many atoms of Y, N subscript Y. After a certain time t, which of the expressions for fraction numerator n u m b e r space o f space d e c a y e d space a t o m s space o f space X over denominator n u m b e r space o f space d e c a y e d space a t o m s space o f space Y end fraction is correct?

    • fraction numerator 3 open parentheses N subscript Y minus N subscript Y open parentheses begin display style 1 half end style close parentheses to the power of begin display style t over T subscript X end style end exponent close parentheses over denominator N subscript Y minus N subscript Y open parentheses begin display style 1 half end style close parentheses to the power of begin display style t over T subscript Y end style end exponent end fraction

    • fraction numerator N subscript X open parentheses 1 half close parentheses to the power of t over T subscript X end exponent space minus space N subscript X over denominator N subscript Y open parentheses 1 half close parentheses to the power of t over T subscript Y end exponent minus N subscript Y end fraction

    • fraction numerator N subscript X open parentheses 1 half close parentheses to the power of t over T subscript X end exponent over denominator N subscript Y open parentheses 1 half close parentheses to the power of t over T subscript Y end exponent end fraction

    • fraction numerator 3 N subscript Y open parentheses 1 half close parentheses to the power of t over T subscript X end exponent over denominator N subscript Y open parentheses 1 half close parentheses to the power of t over T subscript Y end exponent end fraction

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    51 mark

    The initial activity of a radioactive source is 160 counts per second. After a time T, its activity becomes 5 counts per second.

    If the half–life of the source is 18 hours, what is T?

    • 25 hours

    • 90 hours

    • 3.6 hours

    • 1.8 hours

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