Uses of nuclear radiation
Medical tracers (Separate Physics only)
Doctors use to look at organs inside the body. A patient swallows or is injected with a small amount of a radioactive isotope. A detector outside the body follows where it goes, showing whether an organ is working properly.
A good tracer:
- gives out radiation, which passes out of the body to the detector and is only weakly ionising
- has a , of a few hours, so it doesn't stay radioactive in the body for long
Technetium-99m is often used. It gives out gamma rays and has a half-life of about 6 hours. Iodine-123 is used to check the thyroid gland, because the thyroid absorbs iodine.
Key terms
Radiotherapy (Separate Physics only)
uses radiation to kill cancer cells.
- External beams: beams of rays are aimed at the tumour from different angles. They all meet at the tumour, so it gets a high dose while the healthy tissue around it gets much less. The source, such as cobalt-60, has a so it doesn't need replacing often.
- Internal sources: a small radioactive source is placed in or next to the tumour. It gives out or radiation, which doesn't travel far, so it damages the tumour but little else.
Iodine-131, a beta emitter, is used to treat thyroid cancer.
Key terms
Choosing an isotope (Separate Physics only)
| Job | Type of radiation | Half-life |
|---|---|---|
| : escapes the body to reach the detector | Short (hours): doesn't stay active in the body | |
| Gamma: reaches tumours deep inside the body | Long (years): the source lasts | |
| Internal radiotherapy | or : short range, so it only harms nearby cells | Days: active long enough to do the job |
There are always risks. Doctors weigh the benefit to the patient against the harm the radiation could do.
Exam tip
To justify a choice, give both the type of radiation and the half-life, and say why each suits the job.