###### Abstract
Two main pathways leading to radiation exposure of the general public due to a nuclear 'fallout' are the external exposure from radionuclides deposited on the ground, and the internal exposure through contaminated air inhalation, ingestion of contaminated food or water from the affected areas [9]. Radionuclide analysis of environmental samples is very practical for the evaluation of the current environmental radioactivity level. However, in the case of a nuclear accident, it is highly important to evaluate the environmental contamination, as well as the external and internal exposure risks for radiation protection and public health purposes. In the latter case, the risks of an internal exposure are extremely low because of the corresponding international regulations which demand restrictions in food and water intake ([[http://www.mhlw.go.jp/english/topics/2011](http://www.mhlw.go.jp/english/topics/2011) eq/index.html]([http://www.mhlw.go.jp/english/topics/2011](http://www.mhlw.go.jp/english/topics/2011) eq/index.html) (accessed on 29 July 2021)). On the other hand, the risks of external exposure for the public are enforced for safety reasons. The Chernobyl Nuclear Power Plant (CNPP) accident, classified as Level 7 ('major accident') on the International Nuclear and Radiological Event Scale of the International Atomic Energy Agency (IAEA) [10], resulted in a massive release of radionuclides into the atmosphere and caused an extensive contamination of the environment. Ten-day major releases from the Unit 4 of the CNPP injected about 14 EBq of radioactive substances into the atmosphere, including radioactive gases, condensed aerosols, and a large amount of fuel particles. The total release of radioactive substances included the radionuclides: \({}^{132}\)Te, \({}^{134}\)Cs, \({}^{137}\)Cs, \({}^{99}\)Mo, \({}^{103}\)Ru, \({}^{106}\)Ru, \({}^{140}\)Ba, \({}^{95}\)Zr, \({}^{141}\)Ce, \({}^{144}\)Ce, \({}^{89}\)Sr, and \({}^{90}\)Sr. The noble gases contributed about 50% of the total release [11]. A terrestrial surface of more than 200,000 square kilometres in Europe received \({}^{137}\)Cs with levels above 37 kBq m\({}^{-2}\)[12]. Over 70% of the contaminated area comprised Belarus, Russia and Ukraine of the former USSR [13]. The radiation exposure of the population to these biologically dangerous releases was classified into two main phases: the earlier phase included exposure to rapidly decaying radionuclides, whose doses were delivered over a short period (no more than three months after the accident), while the later one comprised of an exposure to radionuclides of a long life that were deposited on the ground [14]. Most of the strontium and plutonium isotopes were deposited within 100 km of the destroyed reactor due to their larger particle sizes, while other important radionuclides decayed away. In the early months after the accident, the radionuclide levels of agricultural plants and plant-consuming animals were dominated by surface deposits [15]. The deposition of \({}^{131}_{~{}53}\)I caused the most immediate concern, but the problem was confined to the first two-three monthsafter the accident because of its decay. The radioiodine was rapidly absorbed into milk, leading to significant thyroid doses in people consuming milk products, especially children in Belarus, Russia and Ukraine. Increased levels of \({}^{131}\)I in milk products were also detected in some southern areas of Europe, while dairy animals were being fed outdoors [16]. Radioisotopes of Caesium (\({}^{137}\)Cs and \({}^{134}\)Cs) were the nuclides which led to the largest problems. The Cs hazard may be attributed to its incorporation into the human body from food consumption (especially dairy products) and via \(\gamma\)-irradiation from the ground. It is characterized by a relatively slow accumulation of doses, compared to radioiodine, but also by a whole-body irradiation [17]. \({}^{131}\)I also concentrates inside the human body through dairy products and has a gamma-component, resulting in a significant whole-body dose.