STUDY ON CONCENTRATION AND DISTRIBUTION OF URANIUM AND THORIUM IN SANDS OF POTENTIAL REGIONS OF BANGLADESH

Abstract

In this study, epithermal neutron activation analysis (ENAA) technique was implemented for the first time at 3 MW TRIGA research reactor of Bangladesh Atomic Energy Commission (BAEC) to determine elemental concentrations in soil/sand samples and characteristically compared it with instrumental neutron activation analysis (INAA) technique to find out advantageous features of ENAA over INAA. The assessment of three parameters (detection limit, analytical sensitivity and Q0 values) using standard reference materials (IAEA-SL-1 and IAEA-Soil-7) indicate that ENAA is more preferable to INAA for the determination of low levels of Arsenic (As), Antimony (Sb), Samarium (Sm) and Uranium (U) in soil/sand samples. In this study, total concentrations of 20 major, minor and trace elements including Th and U in surface and depth-wise inland and beach sands of potential regions of Bangladesh (Cox’s Bazar, Potenga, Kuakata, Moulvibazar, Sylhet, Rajshahi and Sherpur) were determined by INAA and ENAA to deduce origin and extraction possibility of Th and U. The concentration ranges in the beach sands were from 4.63 to 382 mg/kg for Th and from 0.73 to 132 mg/kg for U whereas for inland sand, from 0.55 to 20.8 mg/kg and 0.97 to 4.57 mg/kg, respectively. From the concentration data of Th and U in inland and beach sands, the enrichment factor of Th and U, as well as their extraction possibilities, have been discussed. The depth-wise concentration variations for Th and U in beach and inland sands reveal that the overall U concentration variation decreases top to the deeper layer, but this variation in beach sands is higher than that of the inland sands of Bangladesh. The statistical analysis namely the Pearson correlation study reveals that high levels of Th and U in beach sands are due to the presence of Th and U rich heavy minerals in Cox’s Bazar beach sands. The natural radioactivity concentrations (232Th, 238U and 40K) and radiological hazard indices indicate that average radioactivity concentrations of 232Th and 238U in Cox’s Bazar beach sands are relatively higher than those at other studied areas of Bangladesh as well as the world average values. However, external hazard indices at most of the sampling points are below the safe limit.