One of the tasks of radiation protection is the decontamination of environments polluted by radioactive substances after an accident.
There is contamination every time radioactive substances are present in the environment or on the surface of an object. Contamination can be the source of exposure,external ,by contact or internal.
The contact with a radioactive substance or a close proximity are dangerous.. Beta and above all alpha rays, being only lightly penetrative, the effects will be intense near the skin but will not be felt deep down. An exposure of this type will therefore cause superficial burns. This is what Henri Becquerel discovered involuntarily. Gamma rays being penetrative, the irradiation is spread throughout the organism, but less intense. The maximum effect is close to the point of contact.
It is possible to decontaminate, through a dedicated cleaning, an area, materials and a person who would have been contaminated by contact. The results of the cleaning, dust and other contaminated products taken away will be placed in sealed containers and treated as radioactive waste of low or very low activity.
In the event of a serious accident, one should decontaminate large areas polluted by ground deposition of radioactive particles. At Chernobyl, thousands of liquidators, often poorly protected, cleaned the area around the damaged reactor. At Fukushima, the presence of large amounts of radioactive water had forbidden during long weeks the access to buildings flooded before a decontamination facility to treat these waters was installed.
Internal contamination happens in three ways: through inhalation of substances or radioactive dust; through ingestion, whilst they remain in the absorbed food or deposited on an object brought to the mouth; through injury with a contaminated object or through the infection of an existing wound. It is impossible to decontaminate a person with an internal contamination as it would be too late. We can however limit the effects of it, for example in the case of tritium, by drinking lots of water.
The nuclear workers protect themselves by wearing specific clothes, gloves and masks (that will become radioactive waste). They check that there are no leaks for these items where radioactive substances are found, as well as the renewal of the air of rooms which is filtered to trap the radioactive dust. The manipulation of very radioactive objects should be done done with robots.
Contrary to a popular view, persons contaminated cannot contaminate other persons and therefore they are not a danger to the people treating them.
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