Natural radionuclides and assessment of radiological hazards in MuongHum, Lao Cai, Vietnam

Abstract

²²⁶Ra, ²³⁸U, ⁴ K, and ²³²Th (²²⁸Ra) activity concentrations of 61 soil samples distributed surrounding the rare earth element mine (NORM), MH, Lao Cai, Vietnam have been measured by HPGe detector. The activity concentrations of ²²⁶Ra, ²³⁸U, ⁴ K, and ²³²Th (²²⁸Ra) range from 1179 to 6291 Bq/kg, from 1024 to 8351 Bq/kg, from 260 to 3519 Bq/kg, and from 1476 to 35546 Bq/kg in the ore body and from 21.3 to 964 Bq/kg, from 23.4 to 1635 Bq/kg, from 124 to 3788 Bq/kg, and from 40.9 to 6107 Bq/kg outside the ore body in respective. The study area is considered as the high local natural background radiation with the concentration of ²²⁶Ra, ²³⁸U, ⁴ K, and ²³²Th (²²⁸Ra) of 156, 254, 647, and 908 Bq/kg in respective. Regarding the spatial distribution, the measured radionuclide concentrations are independent of the distance from measured points to the ore body. With regard to the hazard indices, the average calculated radiological hazard indices, including absorbed gamma dose rate, effective dose equivalent, and excess lifetime cancer risk significantly exceed the global average values. There is a disequilibrium between ²³⁸U/²²⁶Ra concentrations in studied soil samples. The results also found that the ²³²Th (²²⁸Ra) concentration and total absorbed gamma dose rate show a strong positive correlation (coefficient of determination, R² = 1).

Keywords: Disequilibrium; High radioactivity; Natural radionuclides; Positive correlation; Radiological hazard; Rare earth mine.