Doctors may use radioactive chemicals called tracers for medical imaging. Certain chemicals concentrate in different damaged or diseased parts of the body, and the radiation concentrates with it. Radiation detectors placed outside the body detect the radiation emitted and, with the aid of computers, build up an image of the inside of the body.
When a radioactive chemical is used in this way it is not normally harmful, because:
Radioactive tracers are also used in hydraulic fracturing. This is the fracturing of underground rock layers (and is often called fracking). A pressurised liquid is forced into the rock layers which fracture and release natural gas which is collected and sold. The tracers help locate the created fractures.