Both radio waves and gamma rays are used in medicine. Give one medical use of gamma rays.

Gamma rays have very high energy and are highly penetrating and ionising. These properties are utilised in several medical applications: - **Sterilisation:** Gamma rays can kill bacteria, viruses, and other microorganisms, making them effective for sterilising medical instruments like syringes and scalpels that cannot be heated. - **Radiotherapy:** A focused beam of gamma rays can be directed at cancerous tumours to kill the cancer cells and shrink the tumour. - **Medical Tracers:** A radioactive substance that emits gamma rays can be injected into or swallowed by a patient. The gamma rays can be detected outside the body by a gamma camera to monitor the function of organs like the kidneys or thyroid.