It is important to note that a vast number of processes are able to release radioactivity into the environment, for example the action of cosmic rays on the air is responsible for the formation of radioisotopes (such as 14C and 32P), the decay of 226Ra forms 222Rn which is a gas which can diffuse through rocks before entering buildings and dissolve in water and thus enter drinking water in addition human activities such as bomb tests, accidents, and normal releases from industry have resulted in the release of radioactivity.
Det er vigtigt at bemærke at en lang række processer er i stand til at frigøre radioaktivitet i miljøet, for eksempel virkningen af kosmiske stråler om luften, er ansvarlig for dannelsen af radioisotoper (såsom 14C og 32P), henfald af 226Ra-former og 222Rn som er en gas der kan diffuse gennem klipperne inden de kommer ind bygninger og opløses i vand og dermed i drikkevand ud menneskelige aktiviteter, såsom bombetests, ulykker, og normal udslip fra industrien har medført udslip af radioaktivitet.