Radiation Safety Officer Practice Test

The largest percentage of background radiation that individuals receive comes from inhalation of radon gas and its daughter products. Radon is a naturally occurring radioactive gas that is produced from the decay of uranium in the earth's crust. It is colorless, odorless, and can accumulate in homes, particularly in basements and poorly ventilated areas.

As people spend a significant amount of time indoors, exposure to radon can lead to a considerable dose of radiation over time. The decay products of radon, known as radon daughters or progeny, can become lodged in the lungs when inhaled and contribute to radiation dose through their radioactive decay.

This factor makes radon exposure the most significant source of natural background radiation for the average person, far exceeding exposures from other sources such as cosmic rays, medical X-rays, and industrial sources. Cosmic rays contribute to a smaller fraction of background radiation, while medical X-rays, although important, are typically not part of natural background exposure and occur due to specific medical procedures. Industrial sources also typically contribute less to the average background radiation dose.