[en] Distribution of the natural radionuclides ( "2"3"8U, "2"3"2Th, and "4"0K) and their specific activities in sands and sediments of the Brahmaputra (Jamuna) river of Bangladesh together with mineral characteristics has been studied to assess the radiation levels as well as to develop a baseline database for comparison in the future in case of any change in the area under study due to anthropogenic activities. The radiological parameters of natural radioactivity were assessed calculating the radium equivalent activity, hazard index, the absorbed dose rate, and annual effective dose. The average activity concentrations of "2"2"6Ra ("2"3"8U), "2"3"2Th, and "4"0K in sand and sediment were found to be 59 ± 2 and 60 ± 2 Bq/kg, 113 ± 5 and 135 ± 5 Bq/kg, and 983 ± 42 and 1002 ± 43 Bq/kg, respectively. The calculated average absorbed dose rate and annual effective dose were found to be 150 nGy/h and 0.18 mSv/year respectively. These high values are associated with mineral content of the sediment. X-ray diffraction peaks of sand and sediment samples identify quartz, feldspar, rutile, zircon, monazite, uranium fluoride, hematite, kyanite, and uranium arsenide minerals to be present in the samples. (author)