Explain why the decay constant of a radioactive nuclide is unaffected by changes in temperature or chemical bonding of the nuclide.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Radioactive decay is a spontaneous process observed in unstable nuclei. Scientists have found that placing a radioactive source in extreme chemical or physical environments does not alter its measured activity.
Model answer (4 marks)
Radioactive decay takes place inside the nucleus and is governed by the strong nuclear force. The electrons and their chemical bonds are far outside the nucleus and only influence the electron cloud. Therefore a change in temperature or a change in chemical bonding can alter the electronic energy levels but has no effect on the nuclear structure or the strong force that determines the decay probability. The decay constant is an intrinsic property of the nucleus, set by its binding energy and nuclear structure, and so it remains unchanged by external chemical or thermal conditions.
Examiner tips
- State that decay is a nuclear process, not an electronic one.
- Explain that temperature/chemical changes affect only electrons, not the nucleus.
- Mention that the decay constant is a property of the nucleus alone.
- Use the phrase "strong nuclear force" or "nuclear binding energy" to show understanding.
Common mistakes
- Confusing the decay constant with the half‑life of a chemical reaction.
- Claiming that temperature can change the decay rate by affecting the nucleus.
- Using vague terms like "environment" without specifying nuclear vs electronic effects.
Mark scheme (4 marks)
- Radioactive decay originates within the nucleus, not from the electron cloud or chemical bonds.
- Temperature changes and chemical bonding only affect the electrons / electron energy levels, not the nucleus.
- The decay constant is a property of the nucleus alone, determined by the strong nuclear force / nuclear binding energy / nuclear structure.
- Because the nucleus is unaffected by these external conditions, the probability of decay per unit time (decay constant) remains constant.
Key terms in this question
Related
- All IB DP Physics Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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