The concentration and spatial distribution of three naturally occurring radionuclides, 238 U, 232 Th and 40 K, has been determined in stream sediments from six left side tributaries of Bistricioara river (Bistriței Mountains, Eastern Carpathians, Romania). Historically, several mining works were undertaken in the area, with a view of exploring its' potential regarding mineral resources. The aim of this study is to serve as a reference point for future environmental monitoring, in the event of resuming the mining activities in this area, which accommodates a major uranium deposit. Stream sediment samples were collected from the riverbed and the concentration of naturally occurring radionuclides was determined using gamma-ray spectrometry with a high purity germanium (HPGe) detector. The average activity concentration of 238 U, 232 Th and 40 K was found to be 27.84, 41.08 and 511.27 Bq•kg −1 . Based on radionuclides' activity concentrations, radiological hazard parameters were estimated in order to assess any radiation risk which may be associated with the riverbed sediments. The radiological hazard parameters, such as radium equivalent activity (Ra eq. ), absorbed gamma dose rates in air (D R ), annual gonadal dose equivalent (AGDE), representative level index (RLI), annual effective dose equivalent (AEDE), external hazard index (H ex ) and internal hazard index (H in ), were all calculated and later compared with international safety limits. Generally, all radiological hazard parameters have values lower than world average excepting AGDE and RLI values that exceed the UNSCEAR thresholds.

The specific activity and spatial distribution of 238U, 232Th and 40K were determined in the surface soil from the Lișava uranium mining sector. This sector belongs to the Banat district, an historically important uranium mining area in Romania (an area with closed uranium mines and a radioactive waste dump). Gamma-ray spectrometry using a high-purity germanium (HPGe) detector was used to measure the activity of naturally occurring radionuclides in the soil. The average specific activities of 238U, 232Th and 40K in the soil were 197.21 Bq/kg for 238U, 16.21 Bq/kg for 232Th and 543.21 Bq/kg for 40K. The mineral contents of selected waste rock samples (sandstones) were examined using a scanning electron microscope (SEM), which revealed that brannerite, pitchblende and coffinite were the most important uranium-bearing minerals. The means of the radiological hazard parameters were calculated to be 262.22 Bq/kg radium equivalent activity (Raeq), 123.72 nGy/h absorbed gamma dose rates (DR), 0.7 external hazard index (Hex) and 1.8 representative level index (RLI). The spatial distribution of the risk assessment indices associated with the investigated soils exceeded the median values provided by UNSCEAR and reflected the geological settings and influences of anthropic activities such as uranium mining practices and the tipping of radioactive mining waste.

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