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 for sterilisation

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.

Medical irradiation

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:

  • maximises the dose on the tumour cells, but
  • minimises the dose on the surrounding soft tissue cells

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.

Person receiving gamma treatment for cancer, with rays being directed to the head.

Efforts are made to ensure that irradiation does not cause any long-term effects. This is done by considering:

Advantages and disadvantages of irradiation


  • sterilisation can be done without high temperatures
  • it can be used to kill bacteria on things that would be damaged by heating


  • it may not kill all bacteria on an object
  • a person standing in the environment where objects are being treated by irradiation could suffer cell damage and cell mutation