Free electrons form the visible light source in a fluorescent light. If we look at visible light produced in this way we are not contaminated by the electrons contained in the glass envelope. Likewise, products ionised by gamma rays from a cobalt-60 source are not contaminated by the radioactive elements contained in the stainless steel tubes.

Within the electromagnetic spectrum, gamma radiation has the greatest energy of all. It is the best suited for destroying the micro-organisms that would otherwise be a health hazard. The level of exposure of a product to gamma radiation is used to control the results which correspond to complete sterilisation in the case of medical supplies, or to pasteurisation in the case of foodstuffs.