Irradiation vs Contamination

Outside the nuclear and scientific community, there is a general misunderstanding that everything exposed to ionizing radiation has been contaminated and is dangerous forever. This is not so. Many of the things you use everyday have been irradiated. Ever use a cotton swab to clean your ear, or a band-aid to protect a cut? Well, it may surprise you to know; both of these products were irradiated or exposed to ionizing radiation to sterilize them. Most people think if something was exposed to ionizing radiation, it must be radioactive. This is simply not the case. There is a big difference between something being irradiated and something becoming contaminated.

When something has been irradiated, by x-rays, gamma rays or electron beams for example, the irradiation stops as soon as the source of ionizing radiation has been removed or terminated. Think of it this way. When you turn a light on, the room is filled with electromagnetic radiation in the form of visible light. The instant you turn the light off, the electromagnetic radiation is gone. The same can be said about the energy of ionizing radiation. (Note: However, even though the irradiation stops, the biological effects may still occur if unrepaired cell damage has been inflicted).

Contamination is much different. When contamination has occurred, the source of the ionizing radiation itself is transferred, such as when radioactive isotopes in solid, liquid or gaseous forms are introduced into the environment. For example strontium-90, a radioactive isotope found in spent reactor fuel which can cause a variety of bone disorders including cancer, can become airborne and settle on buildings, trees and grass, thus contaminating them. Once the strontium-90 has settled it can become mixed with soil and water contaminating them as well. For this reason spent reactor fuel is kept isolated from the environment and in a solid form that cannot be easily dispersed.

nuclear worker
Nuclear worker checking an area for contamination.

When something has been contaminated with radioactive isotopes, it will remain radioactive until the radioactive isotope has decayed to a safe level. In the case of a strontium-90, decades may pass before it decays to a safe level (depending on the initial contamination). If the contamination occurs in a controlled environment such as a building or over a fairly small area, the radioactive isotopes can be cleaned using specialized techniques, equipment and procedures. The contaminated materials must then be properly stored until the isotope involved has decayed into a stable state.

Contamination may not always be dangerous, and can sometimes be useful.  Most living organisms, including plants, are continuously “contaminated” by naturally radioactive isotopes in the environment, such as carbon-14, potassium-40, or uranium-238, during their lifetime.  This contamination leads to a relatively safe level of background irradiation within the organism itself and, even thousands of years later, the decay of carbon-14 can be used to estimate the date of the organism’s death (carbon dating).

In Canada, like most parts of the world, facilities that use ionizing radiation such as nuclear power plants, manufacturing facilities, hospitals, research laboratories, universities and pharmaceutical companies as well as the areas surrounding these facilities are constantly monitored and inspected to insure proper safety procedures are followed. This is done to ensure public safety and to verify that radioactive contamination has not taken place (except where it was intended, under carefully controlled conditions, such as with the use of medical radioisotopes). In the event of an accidental contamination, there are well-practised plans and procedures in place to locate, contain and clean up any contamination that may have taken place. The nuclear industry is the most highly regulated and inspected industry in the world with a safety record that cannot be matched by any other industry.