When you get an x-ray or are near radioactive materials, you are exposed to radiation, but the dose from this exposure stops when the x-ray is over or you move away from the radioactive materials.
Contamination is radioactive material where it is not wanted. An example is nuclear fallout. If the material settles on the skin or is inhaled or ingested, the person can receive a radiation dose. Radiation dose from contamination stops only when the radioactive materials are removed from your body.
Learn more about contamination versus exposure
Some types of radioactive materials stay in the body and are deposited in different body organs where they remain for months or years. Other types are eliminated from the body more quickly in blood, sweat, urine and feces.
Typical radiation exposure (measured in millirem) from different sources:
Radon in indoor air: about 230 millirem per year
Air-food-water: about 30 millirem per year
Medical procedures: about 300 millirem per year
Soils, rocks and cosmic radiation: about 50 millirem per year
The National Council on Radiation Protection and Measurements has captured our average dose in the chart below that shows how much radiation comes from each of the many contributors.