234U/238U Disequilibrium and 235U/238U Ratios Measured Using MC-ICP-MS in Natural High Background Radiation Area Soils to Understand the Fate of Uranium

The Chhatrapur-Gopalpur coastal area in Odisha, India is a well-known natural high background radiation (HBRA) area due to the abundance of monazite (a thorium bearing radioactive mineral) in beach sands and soils. Recent studies on Chhatrapur-Gopalpur HBRA groundwater have reported high concentrations of uranium and its decay products. Therefore, the soils of the Chhatrapur-Gopalpur HBRA are reasonably suspected as the sources of these high uranium concentrations in groundwater. In this report, first the uranium concentrations in soil samples were measured using inductively coupled plasma mass spectrometry (ICP-MS) and they were found to range from 0.61 +/- 0.01 to 38.59 +/- 0.16 mg kg(-1). Next, the U-234/U-238 and U-235/U-238 isotope ratios were measured to establish a baseline for the first time in Chhatrapur-Gopalpur HBRA soil. Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) was used for measurement of these isotope ratios. The U-235/U-238 ratio was observed to be the normal terrestrial value. The U-234/U-238 activity ratio, was calculated to understand the secular equilibrium between U-234 and U-238 in soil and it varied from 0.959 to 1.070. To understand the dynamics of uranium in HBRA soil, physico-chemical characteristics of soil were correlated with uranium isotope ratios and this correlation of U-234/U-238 activity ratio indicated the leaching of U-234 from Odisha HBRA soil.