A patient is given a radioactive tracer containing technetium before a medical scan. 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).
Technetium is a radioactive isotope widely used in hospitals to help produce images of the inside of the body. It has a half-life of 6 hours and is a gamma emitter. Once inside the body, it decays into a safe isotope that can be excreted.
Model answer (5 marks)
Technetium is a suitable tracer because it emits gamma rays, which can penetrate body tissues and be detected externally to create an image.
Its half‑life of 6 h is short enough that the isotope does not remain radioactive for long, minimising radiation dose to the patient.
At the same time the 6‑h half‑life is long enough for the tracer to circulate through the body and be imaged before it decays.
Finally, technetium decays to a non‑radioactive isotope that can be excreted, so it does not leave a residual radioactive source in the body.
Its half‑life of 6 h is short enough that the isotope does not remain radioactive for long, minimising radiation dose to the patient.
At the same time the 6‑h half‑life is long enough for the tracer to circulate through the body and be imaged before it decays.
Finally, technetium decays to a non‑radioactive isotope that can be excreted, so it does not leave a residual radioactive source in the body.
Examiner tips
- Mention gamma emission and external detection first. Balance the half‑life argument: short for safety, long enough for imaging. Include the safe decay product to show no long‑term contamination.
Common mistakes
- Confusing beta with gamma emission. Forgetting to mention the 6‑h half‑life’s dual role. Omitting that the decay product is non‑radioactive and excreted.
Mark scheme (5 marks)
- Technetium is a gamma emitter, so the radiation can pass out through body tissue
- Gamma radiation can be detected outside the body to form an image
- The half-life of 6 hours is short enough that the tracer does not remain radioactive in the body for a long time, reducing harm to the patient
- The half-life is long enough for the tracer to travel through the body and be detected before it decays away
- Technetium decays into a safe isotope that can be excreted by the body, so it does not remain as a source of radioactive contamination
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 →
More Medical imaging questions
- A hospital uses a radioactive tracer to produce images of a patient's internal o…
- A patient requires a medical scan to investigate blood flow through the heart. A…
- A patient with suspected liver disease is given a radioactive tracer that is abs…
- A doctor suspects that a patient has a bone tumour. The patient is given a radio…