Irradiation
Irradiation is the process whereby an item is exposed to radiation. In common usage the term refers to a level of radiation that will be destructive to life, rather than simply exposure to normal levels of radiation, or background radiation.This may happen as the result of a specific nuclear event at a given point. For example, a nuclear bomb being detonated will irradiate a specific area. This is one measure of the destructive power of nuclear bombs. Neutron bombs are specifically designed to irradiate an area, and minimise the mechanical damage to that area. The idea is that all living things will be killed or disabled, but that the resources of the place (buildings, vehicles and the like) will not be destroyed. In practice this is not practical as objects (especially metals) which have been irradiated with neutrons will themselves become radioactive (this is the principle behind neutron activation analysis).
Some forms of radiation will not induce objects to become radioactive. One example of this is gamma rays. Gamma rays are very short wavelength electromagnetic radiation, and are extremely energetic and hostile to life. If used at the correct doses, they can be used to sterilise objects, and this technique is used in the production of medical instruments and disposables, such as syringes.
There has been controversy about the practice of irradiating food. By irradiating the food, some or all microbes in it are killed (depending on dose). This prolongs the life of the food greatly, but can have the disadvantage of killing beneficial microbes. Some foods (e.g., fish) are irradiated at a low dose to avoid killing all spoilage bacteria so that if the food is stored improperly it will begin to smell bad long before botulism bacteria could reach harmful levels (Botulism bacteria are hard to kill, except at such high doses of radiation that the taste of these foods changes). Other foods (e.g., herbs and spices) are irradiated at such high doses (30 kilo-grays or more) that they are completely sterilized. Most foods are irradiated at doses between these levels. It has also been claimed that irradiation can delay the ripening of fruits and vegetables and replace the need for pesticides. However, there is a big BUT in all of this. If any food needed to be irradiated consumers might want to ask what was wrong with it in the first place? Bacterial contamination for example is a sign of bad handling and storage - and there have been some notorious cases of food companies using irradiation to cover up such contamination (cases uncovered by the London Food Commission and documented in "Food Irradiation the Myth and the reality" Tony Webb and Tim Lang, Thorsons 1990) Even irradiation of spices is questionable. How did such spices get so badly contaminated that they needed this 'sterilisation'? Many attempts have been made to paint this as an approved process (see the link below) but the reality is that the technology has little use, is generally rejected by consumers, severely limited in most European and Asian and Australasian countries and - unfortunaely - has more to do with the failing nuclear industry trying to find a rationale for its by products (and nuclear wastes) than anything to do with food safety.
Irradiation is harmful to life as radiation of almost any type in sufficient doses will disrupt or destroy the chemical bonds that make up the molecules of the living thing. Some forms of radiation, such as gamma rays have very high penetrating capabilities, and so can destroy or change crucial molecules in the body, such as those making up internal organs, or DNA molecules. If the DNA is disrupted it may form a cancerous cell by causing mutations to the DNA. Conversely, radiation from space and the sun (Cosmic Background Radiation), as well as background radiation from the earth is responsible for many mutations that help to drive evolution. The key is to find a balance such that mutations are not so common or disadvantageous that they threaten the existence and viability of a species.