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.