Final answer:
External radiation exposure refers to radiation that reaches a person from sources outside the body, which includes cosmic rays, radon gas, and other natural and man-made sources. Protective measures can reduce exposure levels.
Step-by-step explanation:
When radiation reaches a person from sources outside the body, it is known as external radiation exposure. This can occur through various sources such as cosmic rays, soil, building materials, and radon gas. The majority of our exposure comes from natural background radiation, but it can also come from man-made sources such as medical imaging and nuclear accidents. The average annual radiation dose per person in the U.S. is 6.2 millisieverts (620 millirem).
It's important to note that we can minimize our exposure by implementing protective measures such as using shielding materials, increasing distance from the source, and reducing the time spent near the source.