Irradiation and Contamination

There are two ways in which radioactive materials can affect the surrounding environment; irradiation and contamination. Understanding the differences between these two effects is important in terms of the precautions that must be taken when handling radioactive sources and also when storing radioactive waste.

Irradiation refers to the transfer of energy (via ionising radiation) without any direct contact. Before considering the hazards, it is worth noting that this effect can be useful as a way to extend the shelf life of foods that would otherwise decay due to bacterial action or even to kill bacteria that might cause food poisoning. In both cases, the food does not become radioactive (although some foods, bananas being the common example, have a low level of natural radioactivity from the outset). Irradiation can also be used to sterilise heat-sensitive medical instruments that cannot be steam-sterilised in an autoclave. In all of these applications, gamma radiation is used.

The hazards of irradiation stem from the fact that cells can be damaged by ionising radiation without ever coming into direct contact with radioactive materials. Alpha radiation is the most ionising but travels only very short distances and is easily stopped by something as flimsy as a paper bag; beta radiation is less ionising but has a greater penetrating power. In both cases, however, simply moving away from the radiation source reduces the danger considerably. Adding a barrier, such as plastic wrapping when sterilising foods and medical instruments, ensures that the object being irradiated is protected from contamination.

Contamination is considerably more problematic as it causes continuous irradiation that will remain until the source has either been completely removed or its activity has decayed to a safe level. Skin contamination may be hard to remove entirely and ingested materials (inhaled or consumed) will be impossible to extract, resulting in long-term damage or even death. Protective suits are worn by workers who could come into contact with radioactive materials both to reduce immediate irradiation and, far more importantly, to ensure that there is no long-term contamination.

Contamination of the soil, water supplies and the air can also be extremely hard to remove and this is the reason why long-term storage of nuclear waste is so difficult – and such an emotional subject for public debate. More problematic is contamination caused by a nuclear accident and the primary concern is always to ensure that this contamination, especially from radioisotopes with a long half-life, does not enter the food chain.

The probability of harm from nuclear radiation is small in everyday life but the level of potential harm in extreme situations can be severe and appropriate precautions must be taken to limit the adverse impact of both irradiation and contamination.