Contamination vs irradiation

Radiation arriving, or radioactive material arriving?

A radioactive source contains unstable nuclei that emit radiation. Irradiation happens when that radiation reaches an object or person. The source can remain separate: for example, a sealed radioactive source may irradiate someone's hand without any radioactive material getting onto it. Moving away from the source stops that exposure, although any damage already caused by the radiation does not simply disappear. Irradiation alone does not make the hand radioactive.

Contamination is different: radioactive material itself gets onto or into something where it is not wanted. Imagine radioactive dust settling on the hand. The dust is now a source close to the skin, so it can continue to irradiate the hand until it is removed or has decayed. If radioactive material is breathed in or swallowed, it may irradiate tissues from inside the body. Contamination can therefore cause irradiation, but irradiation does not necessarily involve contamination.

Comparing the hazards

Ionising radiation can damage living cells and increase the risk of cancer. With external irradiation, the hazard depends on how much radiation reaches the body and for how long. A nearby source emitting penetrating radiation can be dangerous even though no radioactive material has been transferred. Increasing distance, reducing exposure time or placing suitable shielding between the source and the body can reduce exposure.

With contamination, the material may remain on the skin, clothing or inside the body, so exposure can continue after a person leaves the place where contamination occurred. Radioactive material inside the body is particularly concerning because it is close to living tissue; even poorly penetrating alpha radiation can then cause harm. Removing external contamination reduces the continuing hazard. Neither situation is automatically harmless or always more dangerous than the other: the location of the material, type of radiation and amount of exposure all matter.

The distinction

• Irradiation: radiation reaches an object; radioactive material need not transfer. It does not normally make the object radioactive.
• Contamination: unwanted radioactive material is on or inside an object. That material can continue to irradiate it.

Hazards

Both can expose living cells to damaging ionising radiation. External irradiation stops when the exposure stops, but damage already caused may remain. Contamination may cause prolonged exposure until the material is removed or decays; material inside the body is especially hazardous. Judge the risk from the situation, not the label alone.