Radioactive decay is described as a random process. Explain what is meant by the random nature of radioactive decay and describe how this affects the way in which count rate measurements should be taken in a laboratory experiment.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Radioactive decay is a random process, meaning that
1. It is impossible to predict which nucleus will decay next or exactly when it will decay.
2. The decay of one nucleus is independent of the decay of any other nucleus and is not affected by external conditions.
Because of this randomness, laboratory measurements must:
3. Be carried out over a sufficiently long period or with many repeated readings so that an average (mean) count rate can be obtained.
4. Have the background count rate subtracted from the measured count rate to give the corrected count rate.
1. It is impossible to predict which nucleus will decay next or exactly when it will decay.
2. The decay of one nucleus is independent of the decay of any other nucleus and is not affected by external conditions.
Because of this randomness, laboratory measurements must:
3. Be carried out over a sufficiently long period or with many repeated readings so that an average (mean) count rate can be obtained.
4. Have the background count rate subtracted from the measured count rate to give the corrected count rate.
Examiner tips
- Use the word ‘random’ and explain unpredictability and independence. Show that you understand the need for averaging and background subtraction. Mention that long or multiple measurements reduce statistical error.
Common mistakes
- Assuming a single short measurement gives the true rate. Forgetting to subtract the background count. Confusing random with systematic errors.
Mark scheme (4 marks)
- Cannot predict which nucleus will decay next (or when the next decay will occur)
- The decay of any individual nucleus is independent of / not influenced by other nuclei or external conditions
- Measurements should be taken over a longer time period / multiple readings taken and an average (mean) calculated
- The background count rate must be subtracted from the measured count rate to give the corrected count rate
Key terms in this question
random nature of radioactive decay · count rate
Related
- All Cambridge International IGCSE Physics (0625) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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