###### Abstract
Once inside the body, this radionuclide is absorbed mainly by the thyroid gland, potentially increasing the risk for thyroid cancer, since this gland uses iodine to produce its hormones and cannot distinguish between the radioactive particles and its stable natural form. As \({}^{131}\)I builds up in the thyroid gland, its emitted radiation can induce DNA damage, removing normal limits to cell growth and division and, thus, causing unchecked growth of thyroid tissue [18]. Additionally, the radionuclide \({}^{90}\)Sr (half-life: \(\sim\)28.79 years), due to its chemical similarity to calcium, accumulates in bones and irradiates the bone marrow, and therefore can also cause problems for human health. The latter was concentrated in a more restricted area around the reactor, as its larger particle size and its deposition levels at large distances were not radiologically significant. It is of note that gamma emitter nuclides (such as caesium and iodine isotopes) have been studied more extensively than the beta emitter strontium, since it is much simpler to measure gamma than beta emitters [19]. Therefore, \({}^{137}\)Cs was chosen in our study for the mapping of the deposition because of its radiological importance and its easiness for measurements. Increased contamination levels remained within the atmosphere for years after the accident, while radionuclide deposition values, depending on meteorological and environmental conditions, as well as the particle size, showed a substantial reduction in their transfer to vegetation and animals in agricultural systems during the first few years. The \({}^{137}\)Cs activity concentrations still remain high in the surrounding areas of Chernobyl (in Ukraine, Belarus and Russia), especially in natural ecosystems (forests, rivers and lakes), while the surface contamination and the air dose rate have been reduced significantly due to radioactive decay, rain, wind and human activities [20]. Caesium-137 levels are still present, even in the southern areas of Europe, as monitored through plants such as lichens and mushrooms [21], which have a high retention capacity of such radionuclides; through the lichen Stereocaulon vasuvianum, [PERSON] et al. [22] have accurately determined the effective half-life of \({}^{137}\)Cs. In general, many significant radionuclides released by the CNPP accident have already decayed away. Radioactive iodine isotopes caused great concern within the first few months after the accident since they are short-lived. In the future, \({}^{137}\)Cs will continue to be of greater importance, with less attention paid to \({}^{90}\)Sr. Over the longer term (hundreds of years), the plutonium isotopes and \({}^{241}\)Am will remain radioactive, although at levels that are relatively low [9]. One recent \"major\" (according to IAEA 2008 criteria) nuclear accident occurred in Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan, on 11 March 2011, as a result of a tsunami (caused by a strong earthquake) that struck the east coast of the island. The radioactive releases from this nuclear accident were not as large as those from Chernobyl but were still considered substantial [23]. A radioactive plume derived from the Units 1, 2, 3 and 4 of the FDNPP was dispersed in the atmosphere, causing significant radioactive pollution (mainly due to \({}^{134}\)Cs, \({}^{137}\)Cs and \({}^{131}\)I release) of the environment within a radius of 40 km from the damaged reactors. Immediately after the accident, the prevalent dose-forming radionuclides collected from soil samples from the nearby areas around the reactors were \({}^{131}\)I, \({}^{134}\)Cs, \({}^{137}\)Cs, \({}^{129}\)AmTe, \({}^{95}\)Nb and \({}^{136}\)Cs, while, after several months, the corresponding ones were \({}^{134}\)Cs, \({}^{137}\)Cs and \({}^{129}\)AmTe.