What is a common natural source of background radiation?

A common natural source of background radiation includes cosmic rays and terrestrial sources like radon. Cosmic rays are high-energy particles originating from outer space that constantly bombard the Earth's atmosphere, contributing to the overall radiation exposure we receive. Terrestrial sources refer to radiation that arises from radioactive materials present in the Earth's crust, such as uranium, thorium, and radon gas. Radon, a byproduct of the decay of uranium, can accumulate in homes and buildings, adding to the radiation exposure from natural sources.

In contrast, industrial emissions and chemical spills are related to human activities and not classified as natural background radiation sources. Medical x-rays and CT scans are forms of artificial radiation exposure utilized in medical settings, while geothermal energy and nuclear power plants involve human-engineered processes, thus not being part of the natural background radiation we encounter in our environment. Therefore, the combination of cosmic rays and terrestrial sources accurately captures the essence of natural background radiation.