All three of these methods produce "free radicals." Free radicals are produced when parts of a molecule are knocked off. These damaged molecules become free radicals, which are very reactive and can cause a lot of damage. Free radicals generated in irradiated bacteria damage the bacteria's DNA. The damage to the DNA prevents the bacteria from growing and dividing. When the bacteria are killed then the food stops rotting.
Unfortunately, these free radicals can also damage important nutrients in the food, such as certain vitamins. They also produce unique radiolytic products in food that could potentially be harmful to people. If food is exposed to radiation for too long it will start destroying the food. Some foods, like raw eggs, are changed when irradiated, making them less desirable to eat. Basically, the egg white become white and thicker.
Some radioactive elements emit gamma rays. Radioactive elements are elements that exist in a very unstable state. One example of a radioative element is cesium with a molecular weight of 137. Cesium normally has a molecular weight of about 133. However, when extra weight is added to cesium it makes it very unstable. Cesium prefers to be at 133 and cesium 137 will lose some of its extra weight by losing parts of itself. This is called radioactive decay. When cesium decays it emits gamma rays.
Gamma rays are a very powerful form of energy. Gamma rays can penetrate foods to a depth of several feet. The elements used in irradiation of food (cobalt 60 and cesium 137) do not give off neutrons, which means they do not make anything around them radioactive.
This technology has been used routinely for more than thirty years to sterilize medical, dental and household products, and it is also used for radiation treatment of cancer. The radioactive elements, also called the "radioactive source," do not touch the food.
These radioactive substances emit gamma rays all the time. When not in use, the radioactive "source" is stored in a pool of water, which absorbs the radiation. To irradiate food or some other product the source is pulled up out of the water into a chamber with massive concrete walls that keep any rays from escaping. Medical products or foods to be irradiated are brought into the chamber and are exposed to the rays for a defined period of time. After it is used, the source is returned to the water tank. The food does not become radioactive.
