Assertion: radiation's source | /r/Synonym | background radiation
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Source sentences:
text: These sources, called natural background radiation, consist principally of cosmic rays entering the earth s atmosphere; terrestrial gamma rays due largely to uranium and thorium, including their decay products, found in various low concentrations throughout the earth s crust; potassium 40, a radioisotope which is mixed in small concentrations in nature with stable potassium; and radon decay products.