Analysis of the vertical distribution and size fractionation of natural and artificial radionuclides in soils in the vicinity of hot springs

Lead-210 is a naturally occurring radionuclide of great importance for environmental studies. Its vertical distribution in soil combined with that of Radium–226 may provide useful information on radon exhalation from the ground, or radon carried by ground water. Previous research has shown that natural radioactivity levels–in particular Lead–210 and Radium–226 activity in the ground–may be higher near hot springs. In this work two different locations near hot springs were selected for soil sampling: Kamena Vourla and Thermopylae, both in Greece. Depending on the special soil characteristics of each sampling location, it was decided to collect soil cores up to a depth of 20 cm from Kamena Vourla, and surface soil from Thermopylae.The soil cores were then sectioned into 1 cm slices, while the surface soil samples were separated into seven particle size fractions by dry sieving. All samples were analysed by high resolution gamma-ray spectrometry at the Nuclear Engineering Department of the National Technical University of Athens, using an XtRa germanium detector and a Low Energy germanium detector, to determine: (a) the terrestrial natural radionuclides Thorium–234, Radium–226, Lead-210, Radium–228, Thorium–228 and Potassium–40, (b) the cosmogenic radionuclide Beryllium–7, and (c) the artificial radionuclides Cesium–137 and Ruthenium–106. It is worth mentioning that, the Ruthenium–106 that was detected in samples collected from both sampling locations is the result of an accidental release over Europe, apparently originated in Russia, 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 soil, while at greater depth the concentrations for all radionuclides were as expected. Lead-210 activity was higher than that of Radium–226, showing a disruption in the radioactive equilibrium, as expected. The analysis of the size-fractionated samples showed a higher activity concentration of Lead–210 and Cesium–137 in the finer fractions. The radioactive equilibrium between Thorium–234, Radium–226, and Lead–210 was found to be significantly disturbed in all size fractions.