Speaker
Description
Lead-210 is a naturally occurring radionuclide of great importance for environmental studies. Its vertical distribution in the soil, combined with that of 226Ra, may provide useful information on the radon released to the atmosphere in the region, due to soil radon exhalation, or radon carried by ground water. Previous research has shown that natural radioactivity levels – in particular 210Pb and 226Ra activity in the ground – may be higher near hot springs[1].
In this work, two different locations near hot springs were selected for soil sampling: Kamena Vourla and Thermopylae in Greece. Depending on the special soil characteristics of each sampling location, it was decided to collect soil cores up to a depth of 22 cm from Kamena Vourla, and surface soil from Thermopylae. The soil cores were separated by 1 cm pitch, while the surface soil samples were separated into seven particle size fractions by dry sieving, using a sieving machine and sieves in the range of 0.045-2 mm. All samples were analyzed at the Nuclear Engineering Department of the National Technical University of Athens, by high resolution gamma-ray spectrometry, using an XtRa germanium detector and a Low Energy germanium detector, to determine: (a) the terrestrial natural radionuclides 234Th, 226Ra, 210Pb, 228Ra, 228Th, 40K, (b) the cosmogenic radionuclide 7Be, and (c) the artificial radionuclides 137Cs and 106Ru. It is worth mentioning that the 106Ru that was detected in samples collected from both locations is the result of an accidental release over Europe, a few days before the sampling took place.
The vertical profile of the radionuclides obtained from the core sample analysis indicated a disturbance in the first 7 cm of the soil, while at greater depth the concentrations for all radionuclides were as expected. Lead-210 activity was higher than that of 226Ra, showing a disruption in the radioactive equilibrium, as expected. The analysis of the size-fractionated samples showed – as expected – a higher activity concentration for 210Pb and 137Cs in the finer fractions. The radioactive equilibrium between 234Th, 226Ra, 210Pb was found to be significantly disturbed in all size fractions, suggesting that the cause was mainly hot spring water periodically flooding the sampling terrain.
[1] Beitollahi M, Ghiassi-Nejad M, Esmaeli A, Dunker R. 2007. Radiological studies in the hot spring region of Mahallat, Central Iran. Radiat Prot Dosim 123(4), 505–508
