DISTRIBUTION OF RADIONUCLIDES IN RIVER SEDIMENTS OF KATHMANDU VALLEY, NEPAL AND THE EVALUATION OF ASSOCIATED RADIATION HAZARD.

This article focuses on measuring the activity concentrations of naturally occurring radionuclides potassium-40 (^40K), thorium-232 (^232Th), and uranium-238 (^238U) in sediment samples from rivers and streams throughout the Kathmandu valley. Using gamma-ray spectrometry, the study found average concentrations of 378.54 ± 109.06 Bq/kg for ^40K, 45.95 ± 18.47 Bq/kg for ^232Th, and 26.90 ± 9.61 Bq/kg for ^238U, with variations among different rivers. Radiological hazard indices, including absorbed dose rate, radium equivalent activity, annual effective dose, and internal hazard index, were calculated and found to be below international safety limits, indicating no significant radiological risk from using these sediments as building materials. The study also noted a strong correlation between ^238U and ^232Th concentrations, suggesting the presence of monazite minerals in the sediments.