OCR A Level Physics

Topic Questions

A LevelPhysicsOCRTopic Questions6. Particles & Medical Physics6.9 Radioactivity

6.9 Radioactivity

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A student is modelling the decay of a radioactive source using the equation ΔN / Δt = −0.5 N.
The student decides to use Δt = 0.10 s.
The number N of radioactive nuclei is 2000 at t = 0.

Part of the modelling spreadsheet from the student is shown below.

t / s Number N of radioactive nuclei remaining at time t Number of nuclei decaying in the next 0.10 s
0 2000 100
0.10 1900  
0.20    
0.30    
     

What is the value of N at t = 0.30 s?

  • 1700

  • 1710

  • 1715

  • 1805

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2
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A radiation detector is placed in front of a beta-emitting source.
The count-rate is measured and recorded every 10 minutes.
The results are shown below.

311 s–1 309 s–1 299 s–1 307 s–1  321 s–1


What term can be used to describe the data shown?

  • exponential

  • linear

  • random

  • spontaneous

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3
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The nucleus of thorium-232  open parentheses Th presubscript 90 presuperscript 232 close parentheses emits two alpha particles and two beta-minus particles to become a nucleus of an isotope of radium.

What is the nucleon number A and the proton number Z for the nucleus of this radium isotope?

  • A = 224, Z = 88

  • A = 228, Z = 86

  • A = 224, Z = 84

  • A = 228, Z = 88

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4
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A sample of plutonium-210 has 4.0 ✕ 1010 nuclei.

Given that the initial activity of the sample is 2.3 ✕ 103 Bq, what is the half-life of plutonium-210?

  • 40 ns

  • 3300 days

  • 1.2 s

  • 140 days

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