A hospital uses radioactive tracers to image internal organs. Technetium is commonly used as a medical tracer. Explain why technetium is a suitable radioactive isotope for use as a medical tracer inside the human body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Technetium is a gamma emitter with a half-life of 6 hours. It decays into a stable isotope that can be excreted by the body. It is either injected or swallowed by the patient so that it travels through the body and can be detected externally.
Model answer (5 marks)
1. Technetium emits gamma rays, which can penetrate body tissues and be detected externally.
2. Gamma radiation has the lowest ionising power of the three main types of radiation, so it causes minimal damage to cells.
3. Its half‑life of 6 h is short enough that the isotope decays quickly, reducing long‑term radiation exposure.
4. The same 6 h half‑life is long enough for the tracer to circulate and be imaged before it decays.
5. It decays to a stable isotope that can be excreted, leaving no long‑term radioactive residue in the body.
2. Gamma radiation has the lowest ionising power of the three main types of radiation, so it causes minimal damage to cells.
3. Its half‑life of 6 h is short enough that the isotope decays quickly, reducing long‑term radiation exposure.
4. The same 6 h half‑life is long enough for the tracer to circulate and be imaged before it decays.
5. It decays to a stable isotope that can be excreted, leaving no long‑term radioactive residue in the body.
Examiner tips
- Use the exact wording from the mark scheme (e.g. "gamma emitter", "least ionising power").
- Show the logical link between half‑life and safety/diagnostic time.
- Include both safety and practical imaging aspects in separate points.
Common mistakes
- Confusing gamma with beta or alpha radiation.
- Forgetting to mention the stable decay product.
- Using vague terms like "low radiation" instead of "least ionising power".
Mark scheme (5 marks)
- Technetium is a gamma emitter, so gamma radiation can pass through body tissue to be detected outside the body
- Gamma radiation has the least ionising power, so it causes minimal damage to body tissue / cells
- The half-life of 6 hours is short enough that the technetium decays away quickly, reducing the long-term radiation risk to the patient
- The half-life of 6 hours is long enough for the technetium to travel through the body and be detected before it decays away
- Technetium decays into a stable / safe isotope that can be excreted by the body, so no long-term radioactive material remains inside the patient
Key terms in this question
Related
- All OCR A-Level Physics A (H556) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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