Measurement of naturally occurring radionuclides in geothermal samples and assessment of radiological risks and radiation doses

The analysis of Ra-226, Th-232 and K-40 radionuclides has been carried out in geothermal water and residue samples collected from six wells of geothermal power plant and disposal site, using gamma-spectrometry system equipped with a high-purity germanium detector. The activity concentrations of nine geothermal water samples were found to be lower than minimum detectable activity (MDA) values. The activity concentration of the residue samples ranged from 404 to 269485 Bq kg(1) for Ra-226, 334 to 238885 Bq kg(1) for Th-232, and MDA value to 96730 Bq kg(1) for K-40. In the study, some radiological indexes were examined and found to be higher than the reference values for majority of the residue samples. The annual effective doses arising from some residue samples were calculated to be higher than the permitted dose rate for the public, i.e. 1 mSv y(1).