A hospital uses a radioactive tracer to produce images of a patient's internal organs. The tracer contains technetium, which is a gamma emitter with a half-life of 6 hours. Explain why technetium is a suitable radioactive isotope to use as a medical tracer inside the human body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Medical tracers are substances that contain radioactive isotopes. They are introduced into a patient's body and detected from outside to produce images of internal organs. The choice of isotope used in a tracer must be carefully considered to ensure it is both effective and safe.
Model answer (5 marks)
Technetium is a suitable tracer because it emits gamma rays, which can penetrate body tissue and be detected by external detectors.
Gamma radiation causes less ionisation inside the body, so it minimises damage to healthy cells.
Its half‑life of 6 h is long enough for the tracer to circulate and be imaged, yet short enough that it decays quickly, reducing the long‑term radiation dose.
Finally, technetium decays to a non‑radioactive isotope that can be safely excreted by the body.
Gamma radiation causes less ionisation inside the body, so it minimises damage to healthy cells.
Its half‑life of 6 h is long enough for the tracer to circulate and be imaged, yet short enough that it decays quickly, reducing the long‑term radiation dose.
Finally, technetium decays to a non‑radioactive isotope that can be safely excreted by the body.
Examiner tips
- Use the exact terms "gamma emitter", "half‑life", "ionisation", "safe isotope". Show the logical link between half‑life and safety. Keep the answer concise, matching the 5 marks.
Common mistakes
- Confusing gamma with beta radiation. Forgetting to mention the short half‑life. Using vague phrases like "low radiation" instead of "less ionisation".
Mark scheme (5 marks)
- Technetium is a gamma emitter, so the radiation can pass through body tissue and be detected outside the body
- Gamma radiation causes less ionisation inside the body, reducing damage to healthy cells / tissue
- The half-life of 6 hours is long enough for the tracer to travel through the body and be detected
- The short half-life means the technetium decays away quickly, reducing the long-term radiation dose to the patient
- Technetium decays into a safe isotope that can be excreted by the body
Key terms in this question
tracer · gamma emitter · half-life · isotope
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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