Radiation exposure occurs when all or part of the body absorbs penetrating ionizing radiation from an external radiation source, as shown in the illustration above.
Exposure from an external source stops when a person leaves the area of the source, the source is shielded completely, or the process causing exposure ceases.
Radiation exposure also occurs after internal contamination, i.e., when a radionuclide is ingested, inhaled or absorbed into the blood stream.
This kind of exposure stops only if the radionuclide is totally eliminated from the body, with or without treatment.
An individual exposed only to an external source of radiation, as shown above, is NOT radioactive or contaminated and may be approached without risk, just like after a chest x-ray or CT scan.
Radiation from external exposure alone is either absorbed without the body becoming radioactive, or it can pass through the body completely.
Therefore, if a person is scanned with a radiation survey monitor after external exposure alone, the device will not register radiation above the background level.
