Radioactive contamination is said to have occurred when there is direct contact with radioactive substances.
Irradiation occurs when a person is exposed to 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.