**3. Radiation in the environment**

Radioactive sources are in our body and everywhere outside in the environment. They can be divided in two groups of sources: naturally occurring radionuclides, which are part of naturally occurring radioactive materials (NORM), and technologically enhanced naturally occurring radioactive materials (TENORM). In addition, there are man-made (artificially produced) occurring radioactive materials.

Primordial radionuclides are radionuclides with long half-lives, even longer than the earth's age. They play an important role in the earth's radioactivity. The three natural decay series of Uranium (235U, 238U) and thorium (232Th) belong to them. Secondary radioactive elements are built by the decay of these primordial radionuclides and belong to the inventory of our soils. Some dose-relevant radionuclides of these decay chains are radium (224Ra, 226Ra, and 228Ra), radon (220Rn and 222Rn), lead (210Pb), polonium (210Po), and thorium (228Th, 230Th, and 232Th). Another ubiquitous radionuclide is potassium-40 (40K), Which is a large part to the annual received dose. Cosmogenically produced radionuclides are, for example, beryllium-7 (7 Be), tritium (3 H), or radiocarbon (14C) [8, 9].

Artificial radionuclides have been produced and released to the environment since the 1940s, when nuclear weapons development and tests began in the United States. These tests of nuclear fission in the United States, USSR, China, GB, and France led to fallout with a great number of radioactive fission products and activated radionuclides. Over 600 atmospheric bomb tests from 1945 to 1963 led to a contamination of the Northern Hemisphere with artificial radionu‐ clides such as 14C, 3 H, radiocaesium (134Cs and 137Cs), radiostrontium (90Sr), and plutonium (239Pu). [10]. It is because of scientists, such as Ernest Sternglass, who investigated and proved the negative effects of the bomb fallout on childhood mortality. Their warnings helped to enact the partial test ban treaty,1 which most nuclear powers ratified [11]. After 1965, the fallout clearly decreased. One can clearly see this in sediment profiles of lakes (e.g., lake sediment investigations in Switzerland) [12].

NPPs are also emitters of artificial radionuclides. Several accidents caused the release of large quantities of radioactive fallout to the environment. Accidents were the burn of one pile at the Windscale reactor in Sellafield in 1957, the partial core melting of the Three Mile Island reactor in Harrisburg in 1979, the nuclear catastrophe of the Chernobyl NPP in 1986, and the core meltings of the NPPs of Fukushima-Daiji in Japan 2011. The catastrophe of Chernobyl affected many European countries, many thousands of miles away from the NPP ground.

The use of radionuclides in diagnoses and therapies against cancer leads to the release of shortlived radionuclides, such as iodine (131I), technetium (99mTc), indium (111In), lutetium (177Lu), yttrium (90Y), and others. They do not enter the food chain because of their short half-lives and are therefore of minor concern.
