Total reflection X-ray spectroscopy based detection of uranium and thorium in phosphogypsum simulated by Monte Carlo method

Detection of trace amounts of uranium and thorium in phosphogypsum using total reflection X-ray fluorescence (TXRF) was addressed by Monte Carlo method (MCNP code, version 6.2). The simulated samples contained average concentrations of 238U (120 Bq/kg) and 232Th (40 Bq/kg), as well as 7 major components in oxide forms and other 11 heavy metals in trace amounts, commonly found in PG. It was found that, for a molybdenum target X-ray tube operating under total reflection condition and equipped with an SDD detector, the detection limit for uranium and thorium in the simulated multi-elemental sample are (1.42±0.04)ng and (1.03±0.02)ng, respectively. Based on parameters of certified solutions for uranium and thorium, and adding gallium as an internal standard element, calibration plots provided mass recovery from the multi-component sample with relative errors of 4.56% for uranium and 2.74% for thorium. Our results show that TXRF technique can accurately detect and quantify trace amounts of uranium and thorium in the presence of matrix effects without any pre-treatment of PG samples. •Detection of U and Th in phosphogypsum using TXRF is simulated by the Monte Carlo.•Multi-elemental sample contains 120 Bq/kg of 238U and 40 Bq/kg of 232Th.•Detection limits are (1.42±0.04)ng for U and (1.03±0.02)ng for Th.•Recovered masses of U and Th had relative errors of 4.56% and 2.74%, respectively.•Trace concentrations of U and Th in phosphogypsum can be quantified by TXRF.