I-129 migration and retrospective dosimetry

The naturally occurring of the long-lived radionuclide ¹²⁹I (T_1/2 = 15.7 Ma) have been substantially increased by the fallout from atmospheric nuclear explosions, by releases from nuclear accidents and by emissions from reprocessing plants. The aim of this study was to determine the ¹²⁷I, ¹²⁹I, ⁴⁰K and ¹³⁷Cs in Soils from Northern Ukraine, Chile, Bavaria and the Retrospective Dosimetry of the ¹³¹I exposure after the Chernobyl Accident. In addition, water samples from North Germany (precipitation, surface and ground waters, Aerosol, soils, Humus and milk), North Sea, North Atlantic, Spitzbergen, Indian Ocean, Mediterranean, Hawaii, Tahiti, Egypt and prenuclear sediment samples of the Baltic Sea and the North Sea were analysed. ¹²⁹I/¹²⁷I was analysed by accelerator mass spectrometry (AMS) and ¹²⁷I was determined by inductively coupled plasma mass spectrometry (ICP-MS). The geometric mean deposition density of ¹²⁹I in these soils was 109 x 1.5^±1 mBq m^-2, that the dominant sources of ¹²⁹I in the region are the reprocessing plants (La Hague and Sellafield) and not the Chernobyl fallout. The ¹²⁹I/¹²⁷I isotopic ratios of the Bavarian soils are measured between 10^-7 and 10^-10 what is 100- to 1000-time higher than as the ratios obtained for the Chilean samples. The ¹²⁹I integral deposition densities in Chile, Easter Island and Antarctica were between 0.3 and 2 mBq m^-2. In these soils the observed ¹²⁹I/¹²⁷I ratios are about 10^-12 low measured Value in the pedosphere. This value is consistent with the results from the marine sediments assumed to represent the pre-nuclear equilibrium ratios. The soils from Chile also allow the determination of the ¹²⁹I fallout from the atmospheric nuclear weapons explosions undisturbed from contaminations due to the releases from reprocessing plants. The results from the soil profiles show that more than 90 % of the ¹²⁹I-concentration in the soil profiles are still in the top 40 cm of the profiles is located. This allows the ¹²⁹I inventories in the profiles as approximations for the total anthropogenic ¹²⁹I inventories. The ¹²⁹I- und ¹³⁷Cs-inventories are correlated in the highly contaminated areas. However, the variability of the ratios ¹²⁹I/¹³⁷Cs is large, so that for the retrospective dosimetry of ¹²⁹I-data is drawn. In more than 35 villages in the contamination zone II, the mean thyroid doses were 1.9 x 3.2^±1 Gy for 5-year-old children and 0.45 x 3.2^±1 Gy for adults. In more than 26 locations in the contamination zone III, the mean thyroid doses were 0.75 x 1.9^±1 Gy for 5-year-old child and 0.18 x 1.9^±1 Gy for the adults. The ¹²⁹I/¹²⁷I isotopic ratios in the examined samples from the North Sea and North Atlantic were in the order of 10^-9. They are up to 1000 times higher than in the samples from the Indian and Pacific oceans and as surface water from Egypt. There have also been observed very low ¹²⁹I/¹²⁷I isotopic ratios of 22 x 10^-12 in praenuklearen samples from the Baltic Sea. They are 2 times lower than in the praenuklearen samples from the North Sea. Nevertheless, these values remain greater than the natural ¹²⁹I/¹²⁷I isotopic ratio. The ¹²⁹I/¹²⁷I isotopic ratios took of the sea about the rainfall to the surface water till ground water from 10^-6 to 10^-10 up. It was observed a clear influence of the North Sea on the surface waters in the Great Sea and on the rainfall in Norderney. The ¹²⁹I/¹²⁷I isotopic ratios in milk samples ranged between 77 x 10^-10 and 3 2 x 10^-08. ¹²⁹I/¹²⁷I isotopic ratios the soils of Gorleben stood at 75 x 10^-9 and are up to 3 times smaller than with the associated vegetation. The ¹²⁹I/¹²⁷I isotopic ratios of aerosols ranged between 1.8 x 10^-7 and 2.0 x 10^-7.