What is the primary source of natural background radiation?

The primary source of natural background radiation includes both cosmic rays and terrestrial sources. Cosmic rays are high-energy particles that originate from outer space and interact with the Earth's atmosphere, contributing to the radiation we are exposed to at the surface. Terrestrial sources refer to the radioactive materials present in the Earth's crust, such as uranium, thorium, and potassium-40, which emit radiation as they decay.

Understanding the contributions from both cosmic and terrestrial sources is crucial because they account for the majority of the radiation exposure humans receive in a natural setting. For example, radon gas, which is often considered a significant source of natural radiation, actually falls under the terrestrial category since it is produced by the decay of uranium found in the soil and rocks. Therefore, acknowledging both aspects provides a comprehensive view of natural background radiation and emphasizes the importance of these sources in radiation protection practices.