# Technetium-99m is a radioactive isotope used as a medical tracer. Explain why technetium-99m is well suited for use as a medical tracer, including reference to its type of emission, its half-life, and the difference between irradiation and contamination.

> OCR A-Level Physics B: Advancing Physics (H557) — 6.1 Capacitors · Explain · 5 marks

> Hospitals use radioactive tracers to produce images of the inside of the body. A patient is injected with a small amount of a radioactive substance, which is then detected by scanners outside the body. Technetium-99m has a half-life of 6 hours and is a gamma emitter.

## Mark scheme (5 marks)

1. Technetium-99m is a gamma emitter, so gamma radiation can pass through body tissue to be detected by scanners outside the body.
2. Gamma radiation has the least ionising power, so it causes less damage to healthy cells as it passes through the body.
3. The half-life of 6 hours is long enough for the tracer to travel through the body and be detected, but short enough that it decays away quickly afterwards.
4. The patient is irradiated (not contaminated) by the tracer — irradiation is temporary exposure to radiation and ends once the source has decayed or been removed.
5. Contamination is the unwanted presence of radioactive atoms on or in a material, which is hazardous because those atoms continue to decay; the tracer is designed to be excreted by the body to avoid lasting contamination.

## Key terms

- [half-life](https://www.gradenine.co.uk/glossary/half-life)
- [irradiation](https://www.gradenine.co.uk/glossary/irradiation)

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Source: [GradeNine](https://www.gradenine.co.uk/q/technetium-99m-is-a-radioactive-isotope-used-1291f745) · Published by Druglandscape Ltd.