Which statement about background radiation is true?

The statement regarding background radiation that is true is that natural sources include earth sources and cosmic sources. Background radiation is the radiation that is always present in our environment and comes from both natural and artificial sources.

Natural sources of background radiation primarily come from two categories:

1. Terrestrial Sources: This includes radiation emitted from radioactive materials present in the earth's crust, such as uranium, thorium, and radon gas. These materials naturally decay over time, releasing radiation in the form of alpha, beta, or gamma rays.

2. Cosmic Sources: This type of radiation comes from outer space, where high-energy particles and radiation from the sun and other celestial bodies continuously bombard the Earth's atmosphere. As these cosmic rays encounter the atmosphere, they can create secondary particles that contribute to the background radiation that reaches the surface.

In contrast to this, man-made sources contribute to radiation exposure in different contexts, such as medical procedures (like X-rays) and industrial applications. However, these are not classified as background radiation. Therefore, recognizing that natural sources of background radiation include both terrestrial and cosmic origins is crucial in understanding the overall context of radiation exposure individuals experience daily.