Distribution and radiological risk assessment of natural and artificial radionuclides in soils from the Aktutan hydrothermal alteration zone, Türkiye

This study investigates the distribution of natural radionuclides (226Ra, 232Th, and 40K) and the artificial radionuclide 137Cs in soil samples collected from the Aktutan hydrothermal alteration zone in Gümüşhane, Türkiye. Hydrothermal systems are known to enhance radionuclide mobility and enrichment due to fluid–rock interactions, making them important environments for radiological assessment. However, no previous comprehensive radiological study has been conducted in this region. A total of 12 soil samples were collected and analyzed using high-purity germanium (HPGe) gamma-ray spectrometry. The measured activity concentrations ranged from 16 to 58 Bq·kg−1 for 232Th, 5 to 282 Bq·kg−1 for 226Ra, and 246 to 647 Bq·kg−1 for 40K, while 137Cs was detected in several samples with a maximum value of 5.7 Bq·kg−1. The elevated 226Ra concentrations observed in specific locations may be associated with localized hydrothermal alteration and possible uranium enrichment. Radiological hazard parameters, including absorbed dose rate, annual effective dose, radium equivalent activity, and hazard indices, were calculated. Most values were within internationally recommended limits; however, two sampling sites exhibited elevated radiological risk indicators, particularly in terms of excess lifetime cancer risk. Although the number of samples is limited, the selected locations represent areas of intense hydrothermal alteration and provide preliminary insight into radionuclide distribution in the region. The findings highlight the importance of localized geological controls on radioactivity and suggest the need for continuous environmental monitoring in areas with elevated radionuclide concentrations.