A hospital uses technetium as a radioactive tracer to image internal organs. 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 injected into a patient and its radiation is detected outside the body to build up an image of an internal organ. Technetium has a half-life of 6 hours and is a gamma emitter.
Model answer (5 marks)
Technetium is a suitable tracer because it emits high‑energy gamma rays, which are highly penetrating and can pass through body tissues to be detected by external detectors.
The gamma radiation can be measured outside the patient, allowing an image to be formed.
Its half‑life of 6 h is short enough that the activity falls rapidly, minimising long‑term radiation exposure.
The same half‑life is long enough for the isotope to circulate through the body and reach the target organ before it decays.
Finally, technetium decays to a stable, non‑radioactive isotope that can be safely excreted from the body.
The gamma radiation can be measured outside the patient, allowing an image to be formed.
Its half‑life of 6 h is short enough that the activity falls rapidly, minimising long‑term radiation exposure.
The same half‑life is long enough for the isotope to circulate through the body and reach the target organ before it decays.
Finally, technetium decays to a stable, non‑radioactive isotope that can be safely excreted from the body.
Examiner tips
- Use the exact terms "gamma emitter" and "highly penetrating". Show the balance between short half‑life and sufficient circulation time. Mention that the decay product is safe and can be removed.
Common mistakes
- Confusing beta with gamma emission. Forgetting to state that the decay product is non‑radioactive. Over‑emphasising the half‑life without linking it to safety and detection time.
Mark scheme (5 marks)
- Technetium is a gamma emitter, so the radiation can pass through body tissue without being absorbed / is highly penetrating
- The gamma radiation can be detected outside the body / by a detector placed outside the patient
- The half-life of 6 hours is short enough that the technetium decays / activity dies down relatively quickly, reducing long-term radiation risk to the patient
- The half-life of 6 hours is long enough for the technetium to flow through the body and be detected before it decays away
- Technetium decays into a safe / stable isotope that can be excreted / removed from the body
Key terms in this question
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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