We get irradiated nearly constantly from natural, not natural radiation, and medical sources. The Natural sources of radiation are cosmic, terrestrial and internal. Cosmic radiation originates from space including the sun. Fortunately the atmosphere shields the vast majority of cosmic radiation. Living as I do in Colorado, there is less atmosphere above me so my body gets greater cosmic originated radiation than if I lived at sea level. Terrestrial radiation comes from radioactive elements in the earth’s crust and can vary considerably depending on the presence of these elements where you live. Radon gas is one of the most prevalent.