Background radiation released by soil, rocks and cosmic rays is always in the environment.
Radioisotopes are used as tracers in medicine and industry. Carbon-14 is a radioactive isotope of carbon, which is found in all living organisms. We can estimate the age of dead organisms by measuring the amount of carbon-14 ( 146C ) left in them. Carbon Dating!
Background radiation is all around us. Some of it comes from natural sources and some comes from artificial sources.