The gamma rays come from inside the atoms of these radioactive elements. Doctors use the gamma rays to kill cancer cells. This treatment is called radiotherapy. Engineers use gamma rays to look for cracks in pipes and aircraft parts. They penetrate better than X-rays.
Doctors also use radioactive substances as tracers.
A patient with lung problems can breathe in Xenon-133. Xenon-133 is a gas that emits gamma rays. A special gamma camera uses the rays to build up a picture. The patient only gets a small dose of radiation because they soon breathe out all the gas.