Radioactive exposure and contamination

Radioactive contamination is said to have occurred when there is direct contact with radioactive substances.

Irradiation is said to have occurred when an individual is exposed to the rays from radioactive substances.

If radioactive dust falls onto a person's skin, then the skin is said to have been contaminated. As this radioactive dust emits radiation, it irradiates its surroundings and therefore the contaminated person. Irradiation is therefore a consequence of all contamination.

When a person comes into direct contact with a radioactive substance, radioactive contamination occurs.

When the person moves, the contamination remains on that person and irradiation continues.

The irradiation of the individual continues for as long as the substance remains radioactive and in contact with the person.

We distinguish between external contamination and internal contamination.

External contamination occurs when the radioactive substance comes into direct contact with a person via deposits on the skin, hair or clothing. It can mostly be eliminated by taking a shower and changing your clothes.

Internal contamination is the result of consuming radioactive substances. The radionuclide penetrates inside the body, most often by ingestion or inhalation, but also through skin injuries. These substances attach themselves to tissues or organs and continue to expose them to radiation.

Internal contamination decreases in line with the period of radioactivity of the radionuclide ingested and with biological elimination (e.g. via the urine). In some cases, medication can accelerate the elimination of radioactive substances.

The release of radioactive substances is a consequence of nuclear accidents. These substances disperse in the air in the form of radioactive aerosols and gas.

Anyone outside during the passage of a radioactive cloud will therefore come into direct contact with these substances and risks becoming contaminated.

Radioactive substances are also deposited on the ground when a radioactive cloud passes over. This deposition is higher in the event of rain. Consequently, external contamination of the population remains possible even after the radioactive cloud has passed due to contamination of the ground.

In such a situation, internal contamination occurs by inhaling the aerosols contained in the air and ingesting contaminated food.

Contamination is said to have occurred when there is contact with radioactive substances.

Irradiation is a consequence of all contamination.

External contamination occurs when the source of radiation comes into direct contact with a person via deposits on the skin.

This is caused by:

• the aerosols and radioactive gasses contained in the air when a radioactive cloud passes over;
• radioactive aerosols deposited on the ground (fallout).

It can mainly be eliminated by taking a shower.

Internal exposure is a result of radioactive atoms present in tissues or organs. It therefore occurs from the moment when the atoms enter the body, but decreases in line with the radioactive period of the radionuclide ingested and its distribution throughout the body.

A radionuclide gets inside the body most commonly as a result of ingestion or inhalation, but also through skin wounds or intravenously (for example during a scintigraphy).

Its occurs as a result of:

• inhaling aerosols contained in the air;
• ingesting contaminated food.

In cases of irradiation, the individual is exposed, accidentally or voluntarily, to rays emitted by a source of radiation. When the individual moves out of the field of radiation exposure ceases.

The irradiated person does not become radioactive.

Two types of exposure are possible following a nuclear accident:

• Irradiation (external exposure) from the radioactive cloud and from radioactive substances deposited on the ground;
• Irradiation (internal exposure) from inhaling contaminated air and from consuming contaminated food.

The intensity of the rays emitted by radioactive substances decreases rapidly with distance from the radioactive source. As a result, it is not the rays that escape from a nuclear power station but substances (particles or dust) that are radioactive themselves and are carried by the wind.

The three following measures make up the golden rule for radiation protection so you can protect yourself from radiation from a radioactive source:

• Increase distance : the intensity of radiation decreases rapidly with distance between the individual and the radioactive source ;
• Use the screen effect (take shelter) : solid materials, like a concrete wall or a lead plate, act as a break on rays and therefore reduce their intensity ;
• Limit exposure time : exposure (the dose) increases with the length of exposure.

Four types of exposure are possible following a nuclear accident:

• Irradiation (external exposure) from the radioactive cloud;
• Irradiation (external exposure) from radioactivity deposited on the ground;
• Internal contamination from inhaling aerosols from the radioactive cloud;
• Internal contamination from contaminated food.

In the event of a nuclear accident, employees at the nuclear power station are most exposed to irradiation and at risk of contamination.

Those living close to nuclear power stations also have a risk of higher irradiation and contamination as radioactive particles are diluted by the air with distance.