IGCSE Physics / Applications of radioactivity
Uses of radioactivity in medicine
Edexcel International GCSE Physics (4PH1), chapter 24: Applications of radioactivity, specification point 7.14. Free lesson.
Read the revision notes · IGCSE Physics past papers
Radioactivity is used in medicine for tracers, radiotherapy and sterilising equipment. The radiation type and half-life are chosen to make each use effective while limiting unwanted exposure.
What radioactivity is used for in hospitals
Hospitals use carefully controlled radioactive sources in three main ways. Tracers help doctors see how an organ is working without surgery. Radiotherapy kills cancer cells in a tumour, a lump of cells growing out of control. Sterilising kills bacteria on medical equipment so it is safe to use. A tracer can be used to check the kidneys. Radiotherapy treats a tumour. Sterilising can be used for sealed syringes and other equipment.
How a medical tracer works
A tracer is a radioactive substance followed as it moves through the body. It must give out gamma rays, which are penetrating enough to pass out through the skin and tissue. A gamma camera outside the body detects the rays and makes an image of the organ.
Why tracers need a short half-life
A scan takes only a few hours, so the tracer needs to remain active long enough to produce an image. After the scan, a short half-life makes its activity fall quickly. This reduces how long the patient is exposed to radiation. A long half-life could keep irradiating the patient for days or weeks. Gamma is weakly ionising, so it causes less damage to cells as it passes through the body. Alpha radiation is absorbed inside the body. It would not reach the camera and could damage nearby cells because it is strongly ionising.
How radiotherapy and sterilising use gamma rays
Both uses rely on gamma rays killing cells, but they have different targets. Gamma can penetrate into the body or pass through sealed packaging. Radiotherapy aims gamma beams from several directions so they meet at the tumour. The tumour receives a high dose, while the healthy tissue around it receives less. No surgery is needed, and the patient does not become radioactive. Sterilising exposes the whole sealed pack to gamma rays, killing bacteria on equipment such as syringes and dressings. It works without heat, so plastic is not melted. The equipment does not become radioactive.