A torch beam lights up a person's hand because the hand is exposed to light, which is visible electromagnetic radiation. Exposing objects to beams of radiation is called irradiation. This term applies to all types of radiation, including radiation from the nuclei of atoms.
Irradiation from radioactive decay can damage living cells. However, it can be put to good use as well as being a hazard.
Irradiation can be used to preserve fruit sold in supermarkets. The fruit is exposed to a radioactive source, typically cobalt-60. The gamma rays emitted by the cobalt-60 nuclei destroy bacteria on the fruit without changing the fruit in any significant way. The process does not cause the irradiated object itself to become radioactive.
Doctors use radioactive sources for sterilisation of surgical instruments. They may also use beams of gamma rays to kill cancerous tumour cells deep inside the body. The beams are aimed at the tumour from many different directions. This:
This technique can damage healthy tissue, so careful calculations are done to find the best dose. This is enough to kill tumour cells but not so high that healthy tissue is damaged.
Efforts are made to ensure that irradiation does not cause any long-term effects. This is done by considering: